Engineering Knowledge Test eBook Electrical and Electronics

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Content

Fundamental Engineering •! Engineering Mathematics o! MCQs •! Engineering Physics o! MCQs •! Engineering Drawing o! MCQs Specialisation Branch Topics •! Analog and Digital Electronics o! MCQs •! Electrical Engineering o! MCQs •! Electronic Devices


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o! MCQs •! Control Engineering o! MCQs •! Telecommunication Systems o! MCQs •! Microwave Engineering o! MCQs •! Antenna and Wave Propagation o! MCQs Allied Engineering Topics •! Instrumentation o! MCQs •! Network Theory Design o! MCQs •! Switching Theory o! MCQs


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•! Information Technology o! MCQs •! Radar Theory o! MCQs Previous Year Question Papers •! EKT 1 2015 Electrical and Electronics Paper o! Answers •! EKT 2 2015 Electrical and Electronics Paper o! Answers &

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What does EKT stand for? EKT stands for Engineering Knowledge Test. It is a simple test to check the basic engineering knowledge of candidates applying for IAF technical branch.

Who can attempt EKT? The candidates who are applying for the technical branch of IAF through AFCAT have to attend EKT after general paper.

What does EKT contain? EKT question paper consists of 50 objective type questions from general and specialised engineering topics.

What is the marking scheme in EKT? For every correct answer candidate will get 3 marks, for every wrong answer 1 mark will be deducted.

What is the time duration of EKT? EKT will be of 45 minutes duration.

What if I fail in EKT? Candidates who fail in EKT won’t be eligible for IAF technical branch.

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Engineering Mathematics

Contents 1 Matrix Algebra

2

2 Maxima and Minima

5

3 Multiple integral

5

4 Ordinary differential equation (ODE)

6

5 What is a Statistic? 5.1 Mean and Weighted Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 6

6 Fourier Transforms 6.1 Trigonometric Fourier Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 9

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7 The Discrete Fourier Transform

9

8 Sampling Theorem or Nyquist-Shannon Theorem

10

9 The Laplace transform

10

10 Z-transform

11

1

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1

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Matrix Algebra

Definitions • An array of real numbers is called an m ◊ n matrix with m rows and n columns. S

a11 W a21 W W . W W . W U . am1

T a12 ..... a1n a22 ..... a2n X X . . X X ..... . X X ..... . V am2 amn

The aij is referred to as the i, jth element and denotes the element in the ith row and jth column. If m = n then A is called a square matrix of order n. If the matrix has one column or one row then it is called a column vector or a row vector respectively. • In a square matrix A of order n the diagonal containing the elements a11 , a22 , ..., ann is called the principal or leading diagonal. The sum of the elements in this diagonal is called the trace of A, that is n q trace A = aii i=1

• A diagonal matrix is a square matrix that has its only non-zero elements along the leading diagonal. A special case of a diagonal matrix is the unit or identity matrix I for which a11 = a22 = ... = ann = 1. • A zero or null matrix 0 is a matrix with every element zero.

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• The transposed matrix AT is the matrix A with rows and columns interchanged, is i, jth element being aji .

Properties of addition

• commutative law: A + B = B + A

• associative law: (A + B) + C = A + (B + C)

• distributive law: ⁄(A + B) = ⁄A + ⁄B, scalar

Properties of multiplication • The commutative law is not satisfied in general; that is, in general AB ”= BA. Order matters and we distinguish between AB and BA by the terminology: pre-multiplication of B by A to form AB and post-multiplication of B by A to form BA. • Associative law: A(BC) = (AB)C

• If ⁄ is a scalar then (⁄A)B=A(⁄B)=⁄AB • Distributive law over addition: (A + B)C = AC + BC

A(B + C) = AB + AC Note the importance of maintaining order of multiplication. • If A is an m ◊ n matrix and if Im and In are the unit matrices of order m and n respectively then Im A = AIn = A

Engineering Knowledge Test


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Properties of the transpose If AT is the transposed matrix of A then • (A + B)T = AT + B T • (AT )T = A

• (AB)T = B T AT

Symmetric and Skew-Symmetric Matrices Symmetric and Skew-Symmetric Matrices. Transposition gives rise to two useful classes of matrices. Symmetric matrices are square matrices whose transpose equals the matrix itself. Skew-symmetric matrices are square matrices whose transpose equals minus the matrix.

Example of Multiplication

shop.ssb cra ck.com Rank of a Matrix The rank of a matrix A is the maximum number of linearly independent row vectors of A. It is denoted by rank A.

The last matrix is in row-echelon form and has two nonzero rows. Hence rank A=2,



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Inverse of a Matrix by Determinants The inverse of a nonsingular n ◊ n matrix A = [ajk ] is given by

where Cjk is the cofactor of a jk in det A

The characteristic equation The set of simultaneous equations where A is an n ◊ n matrix and x = [x1 the form

Ax = ⁄x x2

x3 .....xn ]n is an n ◊ 1 column vector can be written in

(⁄I ≠ A)x = 0

where I is the identity matrix. The matrix equation given above represents simply a set of homogeneous equations, and we know that a non-trivial solution exists if c(⁄) = |⁄I ≠ A| = 0

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Here c( Îø ) is the expansion of the determinant and is a polynomial of degree n in ⁄ , called the characteristic polynomial of A. Thus c(⁄) = ⁄n + cn≠1 ⁄n≠1 + cn≠2 ⁄n≠2 + ... + c1 ⁄ + c0

Example Find the characteristic equation for the matrix S T 1 1 ≠2 A = U≠1 2 1 V 0 1 ≠1

the characteristic equation for A is the cubic equation -⁄ ≠ 1 ≠1 2 -⁄≠2 ≠1 -c(⁄) = -- 1 - 0 ≠1 ⁄ + 1-

Expanding the determinant along the first column gives --⁄ ≠ 1 ≠1 -- --≠1 c(⁄) = (⁄ ≠ 1) -≠1 ⁄ + 1- -≠1 3

2

2 -⁄ + 1-

= (⁄ ≠ 1)[(⁄ ≠ 2)(⁄ + 1) ≠ 1] ≠ [2 ≠ (⁄ ≠ 1)]

Thus c(⁄) = ⁄ ≠ 2⁄ ≠ ⁄ + 2 = 0 is the required characteristic equation.



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Partial derivative In mathematics, a partial derivative of a function of several variables is its derivative with respect to one of those variables, with the others held constant (as opposed to the total derivative, in which all variables are allowed to vary). Partial derivatives are used in vector calculus and differential geometry. The partial derivative of a function f(x, y, ...) with respect to the variable x is variously denoted by ˆ ˆf f or ˆx ˆx Since in general a partial derivative is a function of the same arguments as was the original function, this functional dependence is sometimes explicitly included in the notation, as in The partial-derivative symbol is ˆ. One of the first known uses of the symbol in mathematics is by Marquis de Condorcet from 1770, who used it for partial differences. The modern partial derivative notation is by Adrien-Marie Legendre (1786), though he later abandoned it; Carl Gustav Jacob Jacobi re-introduced the symbol in 1841. fxÕ , fx ,

Example Find the partial derivatives fx and fy if f(x , y) is given by f (x, y) = x2 y + 2x + y Assume y is constant and differentiate with respect to x to obtain fx =

ˆf ˆ 2 = [x y + 2x + y] ˆx ˆx

ˆ 2 ˆ ˆ [x y] + [2x] + [y] = [2xy] + [2] + [0] = 2xy + 2 ˆx ˆx ˆx Now assume x is constant and differentiate with respect to y to obtain

shop.ssb cra ck.com fy =

ˆf ˆ 2 = [x y + 2x + y] ˆy ˆy

ˆ 2 ˆ ˆ [x y] + [2x] + [y] = [x2 ] + [0] + [1] = x2 + 1 ˆy ˆy ˆy

2

Maxima and Minima

(Fermat’s Theorem):If f(x) has a local extremum at x=a and f is differentiable at a, then f’(a)=0. The only points at which a function can have a local maximum or minimum are points at which the derivative is zero, Since the derivative is zero or undefined at both local maximum and local minimum points, we need a way to determine which, if either, actually occurs Example Find all local maximum and minimum points for the function Ô f (x) = x3 ≠ x). The derivative Ô is Õ 2 f (x) = 3x ≠ Ô 1. This is defined everywhere and is zero at x = ± 3/3. Looking first at x = 3/3, Ô Ô we see that f ( 3/3 = ≠2 3/9 . Now we test two points on either side of x = 3/3, making sure Ô Ô that neither is farther away than the since 3 = 3, 3/3 < 1 and we can use Ô nearest critical value; Ô x=0 Ô and x=1. Since f (0) f (1) = 0 >Ô≠2 3/9, there must be a local minimum at Ô = 0 > ≠2 3/9 and Ô x = 3/3. For x = ≠ 3/3, we see that f (≠ 3/3) = 2 3/9. This time we can use x=0Ôand x=-1, Ô and we find that f (≠1) = f (0) = 0 < 2 3/9, so there must be a local maximum at x = ≠ 3/3.

3

Multiple integral

The multiple integral is a generalization of the definite integral to functions of more than one real variable, for example, f(x, y) or f(x, y, z). s2s3 Evaluate 1 0 (x2 y) dx dy Engineering Knowledge Test


Page: 6 We will start with

shop.ssbcrack.com s3 0

(x2 y)dx with y constant. I=

⁄

2

1

⁄

0

3

x2 y dx dy

6x=3 x3 = y dy 3 x=0 1 5 2 62 ⁄ 2 9y = (9y)dy = = 18 ≠ 4.5 = 13.5 2 1 1 ⁄

4

2

5

Ordinary differential equation (ODE)

An ordinary differential equation (ODE) is an equation that contains one or several derivatives of an unknown function, which we usually call y(x) (or sometimes y(t) if the independent variable is time (t). The equation may also contain y itself, known functions of x (or t), and constants. For example y Õ = cosx5 y ÕÕ + 9y = e≠2x 3 Õ y Õ y ÕÕÕ ≠ y 2 2 are ordinary differential equations (ODEs). Here, as in calculus, y Õ denotes dy/dx, y ÕÕ = d2 y/dx2 etc. The term ordinary distinguishes them from partial differential equations (PDEs), which involve partial derivatives of an unknown function of two or more variables.

5

shop.ssb cra ck.com What is a Statistic?

In the mind of a statistician, the world consists of populations and samples. An example of a population is all 7th graders in the United States. A related example of a sample would be a group of 7th graders in the United States. In this particular example, a federal health care administrator would like to know the average weight of 7th graders and how that compares to other countries. Unfortunately, it is too expensive to measure the weight of every 7th grader in the United States. Instead statistical methodologies can be used to estimate the average weight of 7th graders in the United States by measure the weights of a sample (or multiple samples) of 7th graders. Parameters are to populations as statistics are to samples. A parameter is a property of a population. As illustrated in the example above, most of the time it is infeasible to directly measure a population parameter. Instead a sample must be taken and statistic for the sample is calculated. This statistic can be used to estimate the population parameter. (A branch of statistics know as Inferential Statistics involves using samples to infer information about a populations.) In the example about the population parameter is the average weight of all 7th graders in the United States and the sample statistic is the average weight of a group of 7th graders. A large number of statistical inference techniques require samples to be a single random sample and independently gathers. In short, this allows statistics to be treated as random variables. A in-depth discussion of these consequences is beyond the scope of this text. It is also important to note that statistics can be flawed due to large variance, bias, inconsistency and other errors that may arise during sampling. Whenever performing over reviewing statistical analysis, a skeptical eye is always valuable. Statistics take on many forms. Examples of statistics can be seen below.

5.1

Mean and Weighted Average

The mean (also know as average), is obtained by dividing the sum of observed values by the number of observations, n. Although data points fall above, below, or on the mean, it can be considered a good estimate for predicting subsequent data points. The formula for the mean is given below as equation (1). The excel syntax for the mean is AVERAGE(starting cell: ending cell).



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qi=n

Xi (1) n However, equation (1) can only be used when the error associated with each measurement is the same or unknown. Otherwise, the weighted average, which incorporates the standard deviation, should be calculated using equation (2) below. q wi xi Xwav = q (2) wi ¯= X

where wi =

1 ‡i 2

i=1

and xi is the data value.

Median The median is the middle value of a set of data containing an odd number of values, or the average of the two middle values of a set of data with an even number of values. The median is especially helpful when separating data into two equal sized bins. The excel syntax to find the median is MEDIAN(starting cell: ending cell).

Mode The mode of a set of data is the value which occurs most frequently. The excel syntax for the mode is MODE(starting cell: ending cell). .

Standard Deviation and Weighted Standard Deviation The standard deviation gives an idea of how close the entire set of data is to the average value. Data sets with a small standard deviation have tightly grouped, precise data. Data sets with large standard deviations have data spread out over a wide range of values. The formula for standard deviation is given below as equation (3). The excel syntax for the standard deviation is STDEV(starting cell: ending cell). ˆ ı i=n ı 1 ÿ ¯ 2 (Xi ≠ X) (3) ‡=Ù n ≠ 1 i=1

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Side Note: Bias Estimate of Population Variance The standard deviation (the square root of variance) of a sample can be used to estimate a population’s true variance. Equation (3) above is an unbias estimate of population variance. Equation (3.1) below is another common method for calculating sample standard deviation, although it is an bias estimate. Although the estimate is biased, it is advantageous in certain situations because the estimate has a lower variance. (This relates to the bias-variance trade-off for estimators.) ˆ ı i=n ı1ÿ ¯ 2 ‡n = Ù (Xi ≠ X) (3.1) n i=1 When calculated standard deviation values associated with weighted averages, equation (4) below should be used.

Example Problem

1 ‡wav = q

wi

(4)

You obtain the following data points and want to analyze them using basic statistical methods. 1,2,2,3,5 Calculate the average: Count the number of data points to obtain n = 5 mean =


1+2+2+3+5 = 2.6 5 Engineering Mathematics

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Obtain the mode: Either using the excel syntax of the previous tutorial, or by looking at the data set, one can notice that there are two 2’s, and no multiples of other data points, meaning the 2 is the mode. Obtain the median: Knowing the n=5, the halfway point should be the third (middle) number in a list of the data points listed in ascending or descending order. Seeing as how the numbers are already listed in ascending order, the third number is 2, so the median is 2. Calculate the standard deviation: Using the equation shown above, Ú 1 ‡= ((1 ≠ 2.6)2 + (2 ≠ 2.6)2 + (2 ≠ 2.6)2 + (3 ≠ 2.6)2 + (5 ≠ 2.6)2 ) = 1.52 5≠1

6

Fourier Transforms

The Fourier transform is important in mathematics, engineering, and the physical sciences. Its discrete counterpart, the Discrete Fourier Transform (DFT), which is normally computed using the so-called Fast Fourier Transform (FFT), has revolutionized modern society, as it is ubiquitous in digital electronics and signal processing. Radio astronomers are particularly avid users of Fourier transforms because Fourier transforms are key components in data processing (e.g., periodicity searches) and instruments (e.g., antennas, receivers, spectrometers), and they are the cornerstores of interferometry and aperture synthesis. The Fourier transform is a reversible, linear transform with many important properties. For any function f(x) (which in astronomy is usually real-valued, but f(x) may be complex), the Fourier transform can be denoted F(s), where the product of x and s is dimensionless. Often x is a measure of time t (i.e., the time-domain signal) and so s corresponds to inverse time, or frequency (i.e., the frequency-domain signal) The Fourier transform is defined by ⁄ Œ F (s) = f (x)e≠2fiisx dx

shop.ssb cra ck.com Œ

which is usually known as the forward transform, and ⁄ Œ f (s) = F (x)e2fiisx dx Œ

Ô which is the inverse transform. In both cases, i = ≠1 . Alternative definitions of the Fourier transform are based on angular frequency (Ê = 2fiv), have different normalizations, or the opposite sign convention in the complex exponential. Since Fourier transformation is reversible, the symmetric symbol … is often used to mean ”is the Fourier transform of”; e.g., F (s) … f (x). The complex exponential is the heart of the transform. A complex exponential is simply a complex number where both the real and imaginary parts are sinusoids. The exact relation is called Euler’s formula ei„ = cos„ + isin„ which leads to the famous (and beautiful) identity eifi +1 = 0 that relates five of the most important numbers in mathematics. Complex exponentials are much easier to manipulate than trigonometric functions, and they provide a compact notation for dealing with sinusoids of arbitrary phase, which form the basis of the Fourier transform. Complex exponentials (or sines and cosines) are periodic functions, and the set of complex exponentials is complete and orthogonal. Thus the Fourier transform can represent any piecewise continuous function and minimizes the least-square error between the function and its representation. There exist other complete and orthogonal sets of periodic functions; for example, Walsh functions (square waves) are useful for digital electronics. Why do we always encounter complex exponentials when solving physical problems? Why are monochromatic waves sinusoidal, and not periodic trains of square waves or triangular waves? The reason is that the derivatives of complex exponentials are just rescaled complex exponentials. In other words, the complex exponentials are the eigenfunctions of the differential Engineering Knowledge Test


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operator. Most physical systems obey linear differential equations. Thus an analog electronic filter will convert a sine wave into another sine wave having the same frequency (but not necessarily the same amplitude and phase), while a filtered square wave will not be a square wave. This property of complex exponentials makes the Fourier transform uniquely useful in fields ranging from radio propagation to quantum mechanics.

6.1

Trigonometric Fourier Series f (t) =

Œ ÿ

(an cos(Ê0 nt) + bn sin(Ê0 nt))

n=1

where a0 =

1 T

⁄

T

0

f (t)dt, an =

bn =

2 T

⁄

0

T

2 T

⁄

T

0

f (t)cos(Ê0 nt)dt

f (t)sin(Ê0 nt)dt

Example: Fourier Transform of a Cosine

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7

The Discrete Fourier Transform

The continuous Fourier transform converts a time-domain signal of infinite duration into a continuous spectrum composed of an infinite number of sinusoids. In astronomical observations we deal with



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signals that are discretely sampled, usually at constant intervals, and of finite duration or periodic. For such data, only a finite number of sinusoids is needed and the Discrete Fourier Transform (DFT) is appropriate. For almost every Fourier transform theorem or property, there is a related theorem or property for the DFT. The DFT of N uniformly sampled data points xj (where j = 0, ..., N ≠ 1) and its inverse are defined by N ≠1 ÿ Xk = xj · e≠i2fikj/N n=0

xj =

N ≠1 1 ÿ Xk · ei2fikn/N N k=0

Once again, sign and normalization conventions may vary, but our definition is the most common. The continuous variable s has been replaced by the discrete variable (usually an integer) k.

8

Sampling Theorem or Nyquist-Shannon Theorem

This theorem states that any continuous baseband signal (signal extending down to zero frequency) may be identically reconstructed if the signal is bandwidth limited and the sampling frequency is at least twice the bandwidth of the signal (i.e. the highest frequency of a baseband signal). That critical sampling rate, 1/ t, where t is the time between successive samples, is known as the Nyquist rate, and it is a property of the time-domain signal based on its frequency content. Somewhat confusingly, if a time-domain signal is sampled uniformly, then the frequency corresponding to one-half that rate is called the Nyquist frequency VN/2 = 1/(2 t)

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The Nyquist frequency describes the high frequency cut-off of the system doing the sampling, and is therefore a property of that system. Any frequencies present in the original signal which are at higher frequencies than the Nyquist frequency will be aliased to other lower frequencies in the sampled band as described below. If that signal was band-limited and then sampled at the Nyquist rate, in accordance to the Sampling Theorem, no aliasing will occur.

9

The Laplace transform

We define the Laplace transform of a function f(t) by the expression ⁄ Œ L[f (t)] = F (s) = e≠st f (t)dt 0

where s is a complex variable and e≠st is called the kernel of the transformation. Since the upper limit in the integral is infinite, the domain of integration is infinite. Thus the integral is an example of an improper integral



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10

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Z-transform

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In mathematics and signal processing, the Z-transform converts a discrete-time signal, which is a sequence of real or complex numbers, into a complex frequency domain representation. It can be considered as a discrete-time equivalent of the Laplace transform. This similarity is explored in the theory of time scale calculus. The Z-transform, like many integral transforms, can be defined as either a one-sided or two-sided transform. Bilateral Z-transform The bilateral or two-sided Z-transform of a discrete-time signal x[n] is the formal power series X(z) defined as X(z) = Z{x[n]} =

Œ ÿ

x[n]z ≠n

n=≠Œ

where n is an integer and z is, in general, a complex number: z = Aej„ = A(cos „ + j sin „) where A is the magnitude of z, j is the imaginary unit, and „ is the complex argument (also referred to as angle or phase) in radians. Unilateral Z-transform Alternatively, in cases where x[n] is defined only for n Ø 0, the singlesided or unilateral Z-transform is defined as X(z) = Z{x[n]} =

Œ ÿ

x[n]z ≠n .

n=0

In signal processing, this definition can be used to evaluate the Z-transform of the unit impulse response of a discrete-time causal system.



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Inverse Z-transform The inverse Z-transform is x[n] = Z ≠1 {X(z)} =

1 2fij

j

X(z)z n≠1 dz

C

where C is a counter clockwise closed path encircling the origin and entirely in the region of convergence (ROC). In the case where the ROC is causal , this means the path C must encircle all of the poles of X(z). Example 1 Let x[n] = (0.5)n . Expanding x[n] on the interval (≠Œ, Œ) it becomes ) * ) * x[n] = · · · , 0.5≠3 , 0.5≠2 , 0.5≠1 , 1, 0.5, 0.52 , 0.53 , · · · = · · · , 23 , 22 , 2, 1, 0.5, 0.52 , 0.53 , · · · . Looking at the sum

Œ ÿ

n=≠Œ

x[n]z ≠n æ Œ.

Therefore, there are no values of z that satisfy this condition.

Parseval’s theorem Œ ÿ

x1 [n]xú2 [n]

n=≠Œ

=

1 j2fi

j

C

X1 (v)X2ú ( v1ú )v ≠1 dv

Initial value theorem:

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If x[n] is causal, then

x[0] = lim X(z). zæŒ

Final value theorem: If the poles of (z-1)X(z) are inside the unit circle, then x[Œ] = lim (z ≠ 1)X(z). zæ1



Engineering'Knowledge'Test'

'

Engineering'Mathematics'MCQs'

Engineering'Mathematics'MCQs' ! Linear'Algebra'(matrices)' ! 1.'''For'any'two'matrices'A'and'B,'which'of'the'following'is'correct?' (a)' !" = 0% ⇒ ! = 0%'(%" = 0' (b)' ! + " * = !* + 2!" + " * ' (c)' !" , = " , !, ' (d)' ∣ !" ∣%%≠∣ ! ∣%∣ " ∣%%' ' 2.''A'5'X'7'matrix'has'all'its'entries'equal'to'J1.'Then'the'rank'of'a'matrix'is' (a)' 7' (b)' 5' (c)' 1' (d)' Zero' ' 0 1 3.'''The'eigen'value'of'the'matrix'[% ]'are' 1 1 (a)' (a+1),0' (b)' a,0' (c)' (aJ1),0' (d)' 0,0' ' 4.'The'rank'of'(mxn)'cannot'be'more'than' (a)' m' (b)' n' (c)' mn' (d)' All'of'the'above' ' 5.''In'the'GaussJelimination'for'a'solving'system'of'linear'algebraic'equations,' triangularization'leads'to' (a)' Diagonal'matrix' (b)' Lower'triangular'matrix' (c)' Upper'triangular'matrix' (d)' Singular'matrix' ' 6.''If'A'and'B'are'two'matrices'and'if'AB'exist'then'BA'exists.' (a)' Only'if'A'has'as'many'rows'a'B'has' (b)' Only'if'both'A'and'B'are'square' columns' matrices' (c)' Only'if'A'and'B'are'skew'matrices' (d)' Only'if'both'A'and'B'are'symmetric' ' 7.''If'A'is'a'real'square'matrix'the'AAT'is' (a)' UnJsymmetric' (b)' Symmetric' (c)' SkewJsymmetric' (d)' PartiallyJsymmetric' ' 8.''If'A,'B,'C'are'square'matrices'of'the'same'order'then'(ABC)J1'is'equal'to' (a)' CJ1AJ1BJ1' (b)' CJ1BJ1AJ1'' (c)' AJ1BJ1'CJ1' (d)' AJ1'CJ1BJ1' ' 1 1 9.''The'rank'of'the'matrix'[ ]'is' 0 0


'

(a)' 4' (c)' 1'


(b)' 2' (d)' 0'

' 10.'A'system'of'equations'represented'by'AX=0'where'X'is'a'column'vector'of'unknown' and'A'is'matrix'containing'has'a'nonJtrivial'solution'when'A'is' (a)' NonJsingular' (b)' Singular' (c)' Symmetric' (d)' Hermitian' ' Differential!equation! ! ' 345

35

11.'The'differential' 4 + + 789: = 0'is' 36 36 (a)' Linear' (b)' NonJlinear' (c)' Homogeneous' (d)' Of'degree'two' ' 35 12.'For'the'differential'equation' + 5: = 0'with'y(0)'=1,'the'general'solution'is' 3, (a)' < =, % (b)' < >=, % (c)' 5< >=, % (d)' < >=, ' ' 13.'The'solution'of'the'first'order'differential'equation'? @ = % −3%? @ , ? 0 = ?D %87%? @ = % ___.' (a)' ?D %< >G, ' (b)' ?D %< >G % (c)' ?D %< >,/G % (d)' ?D %< >, ' ' 345

14.'For'the'differential'equation,'3 4 + 4 3, (a)' Degree'='2,'order'='1' (c)' Degree'='4,'order'='3' '

35 *

+ : * + 2 = ?'' (b)' Degree'='1,'order'='2' (d)' Degree'='2,'order'='3'

3,

346

15.'The'degree'of'the'differential'equation' 4 + 2? G = 0'is' 3, (a)' 0' (b)' 1' (c)' 2' (d)' 3' ' 35 16.'The'solution'of'differential'equation' = J:, : 0 = K'is' 36 L5 (a)' ? = K< ' (b)' ? = J< M5 % (c)' : = < N6 K% (d)' : = K< >N6 ' ' 17.'The'one'dimensional'heat'condition'partial'differential'equation'

OP O,

=%

O4P O6 4

'is'


'

(a)' Parabolic' (c)' Elliptic'


(b)' Hyperbolic' (d)' Mixed'

' 18.''A'partial'differential'equation'requires' (a)' 'exactly'one'independent'variable' (b)' '''two'or'more'independent'variables' (c)' 'more'than'one'dependent' (d)' 'equal'number'of'dependent'and' variable' independent'variables' ' 19.'The'solution'of'the'partial'differential'equation'yzp+zxq=xy'is'given'by' (a)' x2+y2=c1'and'x2+z2=c2' (b)' x2−y2=c1'and'x2−z2=c2' (c)' x2+y2=c1'and'x2−z2=c2' (d)' x2−y2=c1'and'x2+z2=c2' ' 20.'Let'f'='yx.'what'is' (a)' 0' (c)' 1'

O4Q

O6O5

'at'x'='2,'y'=1?' (b)' ln2' (d)' 1/ln2'

' Complex!vcariables! ! 21.!The'real'part'of'the'complex'number'z'='x'+'iy'is'given'by' T − T∗ (a)' R<(T) % = %T%% − %T ∗% (b)' R< T = % % 2 T + T∗ (c)' (d)' R< T = %T% + %T ∗' R< T = % % 2 i 22.''i ,'where'8 = −1'is'given'by' (a)' 0' (b)' < >W* ' (c)' < >W* '

' 23.'ez'is'a'periodic'with'a'period'of'' (a)' 2X' (c)' X% ' Z>[ 24.'The'bilinear'transformation'Y = % '' Z\[ (a)' Maps' the' inside' of' the' unit' circle' in' the' zJplane' to' the' left' half' of' the'wJplane' (c)' Maps' the' inside' of' the' unit' circle' in' the' zJplane' to' the' right' half' of' the'wJplane' '

(d)' 1'

(b)' 2X8% (d)' 8X'

(b)' Maps'the'outside'of'the'unit'circle'in' the' zJplane' to' the' left' half' of' the' wJ plane' (d)' Maps'the'outside'of'the'unit'circle'in' the'zJplane'to'the'right'half'of'the'wJ plane'


'


25.'Let'= % −1'.'Then'one'value'of'jj'is'' (a)' 3' (b)' J1' (c)' 1 (d)' < >W/* ' ' 2 ' ]^_ Z 26.'For'the'function' ` 'of'a'complex'variable'z,'the'point'z'='0'is' Z (a)' A'pole'of'order'3' (b)' A'pole'of'order'2' (c)' A'pole'of'order'1' (d)' Not'a'singularity' ' >=\a[D

27.'The'value'of'the'expression' %' G\ba (a)' 1J2i' (c)' 2Ji' ' 28.'The'equation'Sin(z)'='10'has' (a)' No'real'(or)'complex'solution' (c)' A'unique'solution'

(b)' 1+2i' (d)' 2+i' (b)' Exactly'two'distinct'complex' solutions' (d)' An'infinite'number'of'complex' solutions'

' [ 29.'If'a'complex'number'c'satisfies'the'equation'cG = 1'then'the'value'of''1 + c + '' d is'___.' (a)' 0' (b)' 1' (c)' 2' (d)' 4' ' 30.'If'Z'='x+jy''where'x,y'are'real'then'the'value'of' < eZ 'is' (a)' 1' (b)' < 6 4 \5 4 ' (c)' < 5 ' (d)' < >5 ' ' Laplace!transform! ' d 31.'The'Laplace'transform'for'f(t)''is'F(s).'Given' 7 = % 4 4 ','the'final'value'of'f(t)'is' f \d ____.' (a)' Initially'' (b)' Zero' (c)' One' (d)' None' ' 32.'(s+1)J2'is'the'Laplace'transform'of'' (a)' t2' (b)' t3' (c)' eJ2t' (d)' teJt'


' 33.'If'g h @

=%

i f 4 \i 4

'


'then'the'value'of' lim h @ = % ___''

(a)' Can'not'be'determined' (c)' Unity'

,→n

(b)' Zero' (d)' Infinite'

' 34.'If'g h @ − o = p 7 'then'g h @ − o 'is'equal'to'' (a)' esT'F(s)' (b)' eJsT'F(s)' p(7) (c)' p(7) (d)' ' ' 1 − < fP 1 − < >fP ' 35.'Let'Y(s)'be'the'Laplace'transform'of'function'y(t),'then'the'final'value'of'the'function' is'_____.' (a)' lim q(7)' (b)' lim q(7)' f→D

(c)' lim q(7)% f→[

(d)'

f→n

lim q(7)'

f→>[

' 36.'The'Laplace'transform'of'i(t)'is'given'by'I(s)'='2/s(1+s)''As'@ → ∞','the'value'of'i(t)' tends'to'___.' (a)' 0' (b)' 1' (c)' 2' (d)' infinity' ' 37.'If'F(s)'is'the'Laplace'transform'of'the'function'f(t)'then'Laplace'transform'of' , h ? s? ''is' D (a)' 1/s'F(s)' (b)' 1/s'F(s)]Jf(0)' (c)' sF(s)Jf(0)' (d)' JsF(s)' ' 38.'Laplace'transform'of'Sinht'is' (a)' 1/(s2J1)' (b)' 1/(1Js2)' (c)' s/(s2J1)' (d)' s/(1Js2)' ' [ 39.'The'inverse'Laplace'transform'of' 4 ''is' f \f (a)' 1+et' (b)' 1Jet' (c)' 1JeJt' (d)' 1+eJt' ' 40.'U(t)'represents'the'unit'step'function.'The'Laplace'transform'of't(@ − u)'is' 1 (a)' 1 (b)' ' % 7u 7−u (c)' < >fv (d)' < >fv ' ' ' 7 '


'


Calculus! ! 41.'The'area'bounded'by'the'parabola'2y=x2'and'the'lines'x=yJ4'is'equal'to'____.' (a)' 6' (b)' 18' (c)' Infinity' (d)' None'of'the'above' ' 42.'If'at'every'point'of'a'certain'curve,'the'slope'of'the'tangent'equals'J2x/y,'the'curve'is' ____.' (a)' A'straight'line' (b)' A'parabola' (c)' A'circle' (d)' An'ellipse' ' 43.'What'is'the'average'value'of'the'function''g(x)'='(2x+3)2'on'the'interval'from'x'='J3'to' x'='J1?' (a)' 7/3' (b)' J4' (c)' 5' (d)' 3' ' [ 44.'lim ?789( ) = % ____.' 6

6→D

(a)' Infinity' (c)' 1'

(b)' 0' (d)' Can'not'be'determined'

% 45.'If'a'function'is'continuous'at'a'point'its'first'derivative' (a)' May'or'may'not'exist' (b)' Exist'always' (c)' Exists'at'infinity' (d)' Exist'at'unique'value' ' 46.'The'function'f(x)'='ex'is'___.' (a)' Even' (b)' Odd' (c)' Neither'even'or'odd' (d)' None'of'the'above' ' 47.'lim

6→D

wax4 6 6

(a)' 0' (c)' 1'

'='___' (b)' Infinity' (d)' J1'

' 48.'The'area'enclosed'between''the'parabola'y=x2'and'the'straight'line'y=x'is'___.' (a)' 1/8' (b)' 1/6' (c)' 1/3' (d)' 1/2' ' ' 49.'For'the'function'f(x)'='x2eJx,'the'maximum'occurs'when'x'is'equal'to'___.' (a)' 2' (b)' 1'


'

(c)' 0'


(d)' J1'

' 50.'For'real'values'of'x,'the'minimum'value'of'f(x)'='ex+eJx'is' (a)' 2' (b)' 1' (c)' 0.5' (d)' 0' ' ' Answers:!Engineering!Mathematics!MCQs! ! 1.!!(c)!

2.!(c)!

3.!(a)!

4.!(d)!

5.!(c)!

6.!(a)!

7.!(b)!

8.!(b)!

9.!(c)!

10.!(b)!

11.!(b)! 12.!(b)! 13.!(a)! 14.!(b)! 15.!(b)! 16.!(c)! 17.!(a)! 18.!(b)! 19.!(b)! 20.!(c)! 21.!(c)! 22.!(c)! 23.!(b)! 24.!(a)! 25.!(d)! 26.!(b)! 27.!(b)! 28.!(d)! 29.!(a)! 30.!(d)! 31.!(b)! 32.!(d)! 33.!(b)! 34.!(b)! 35.!(c)! 36.!(d)! 37.!(a)! 38.!(a)! 39.!(c)! 40.!(c)! 41.!(b)! 42.!(d)! 43.!(a)! 44.!(b)! 45.!(a)! 46.!(c)! 47.!(a)! 48.!(b)! 49.!(a)! 50.!(a)! '

Engineering Physics

Contents 1 Units for measurement 1.1 Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 3

2 Description of motion in dimensions

6

3 Motion in one dimension

8

4 Laws of motion 4.1 Newton first law of motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Newton second law of motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Newton third law of motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 9 9 10

5 Work, energy and Power

11

6 Rotational motion

12

7 Gravitation 7.1 Kepler’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13 13

8 Heat and Thermodynamics 8.0.1 Ideal gas equation 8.0.2 Thermal expansion 8.1 Specific heat capacity . . 8.2 Thermodynamics . . . . . 8.3 Electrostatics . . . . . . . 8.4 Electric current . . . . . . 8.4.1 Ohm’s law . . . . . 8.5 Magnetism and gauss law 8.6 Electromagnetic induction 8.7 Alternating current . . . .

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14 14 15 15 16 17 19 19 24 24 26

9 ELECTROMAGNETIC WAVES 9.1 ELECTROMAGNETIC SPECTRUM 9.2 Radio waves . . . . . . . . . . . . . . . 9.3 Microwaves . . . . . . . . . . . . . . . 9.4 Infrared waves . . . . . . . . . . . . . 9.5 Visible Rays . . . . . . . . . . . . . . . 9.6 Ultraviolet rays . . . . . . . . . . . . . 9.7 X-rays . . . . . . . . . . . . . . . . . . 9.8 Gamma rays . . . . . . . . . . . . . .

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Page: 2 10 RAY OPTICS AND OPTICAL INSTRUMENTS 10.1 REFRACTION . . . . . . . . . . . . . . . . . . . . . 10.2 TOTAL INTERNAL REFLECTION . . . . . . . . . 10.3 Total internal reflection in nature . . . . . . . . . . . 10.4 Power of a lens . . . . . . . . . . . . . . . . . . . . . 10.5 DISPERSION BY A PRISM . . . . . . . . . . . . .

. . . . .

29 30 30 30 31 31

11 OPTICAL INSTRUMENTS 11.1 The microscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Telescope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Engineering Physics

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Units for measurement

Definition : Things in which quantity is measured are known as units. Measurement of physical quantity = (Magnitude) ◊ (Unit) Measurement of any physical quantity involves comparison with a certain basic, arbitrarily chosen, internationally accepted reference standard called unit. The result of a measurement of a physical quantity is expressed by a number (or numerical measure) accompanied by a unit. Although the number of physical quantities appears to be very large, we need only a limited number of units for expressing all the physical quantities, since they are interrelated with one another. The units for the fundamental or base quantities are called fundamental or base units. The units of all other physical quantities can be expressed as combinations of the base units. Such units obtained for the derived quantities are called derived units. A complete set of these units, both the base units and derived units, is known as the system of units. In earlier time scientists of different countries were using different systems of units for measurement. Three such systems, the CGS, the FPS (or British) system and the MKS system were in use extensively till recently. The base units for length, mass and time in these systems were as follows : • In CGS system they were centimetre, gram and second respectively. • In FPS system they were foot, pound and second respectively.

• In MKS system they were metre, kilogram and second respectively. SI Base Quantities and Units

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1.1

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Dimensions

Dimensions of a physical quantity are the powers to which the fundamental quantities must be raised to represent the given physical quantity. Illustration : F orce(quantity) = mass ◊ acceleration F orce(quantity) = mass ◊

velocity length = mass ◊ time times2

F orce(quantity) = mass ◊ length ◊ (times)≠2

Hence, dimensions of force in ; mass is 1 ; length is 1 ; time is -2. So the dimensional formula of force is M LT ≠2 Dimensional Formula : It is an expression which shows the unit of a physical quantity using fundamental units. Quantities with units, symbol and dimensional formula

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Engineering Physics

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Engineering Physics

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Description of motion in dimensions

Motion is change in position of an object with time.In order to specify position, we use a reference point and a set of axes ( rectangular coordinate system).The coordinates of an object describe the position of the object with respect to this coordinate system. To measure time, we position a clock in this system. If only one coordinate of an object changes with time , we say that the object is in one dimensional motion .If only two coordinates of an object changes with time , we say that the object is in two dimensional motion and if three coordinates of the object changes with time it represent three dimensional motion.

Displacement Defined as the change in the position of an object. Let x1 and x2 be the positions of an object at time t1 and t2 . Then its displacement, denoted by x, in time t = (t2 ≠ t1 ), is given by the difference between the final and initial positions : x = x2 ≠ x1

If x2 > x1 , x is positive; and if x2 < x1 , x is negative. Displacement has both magnitude and direction. Such quantities are represented by vectors.

Uniform motion If an object moving along the straight line covers equal distances in equal intervals of time, it is said to be in uniform motion along a straight line.

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Position-time graph of uniform motion

Average velocity Average velocity is defined as the change in position or displacement ( x) divided by the time intervals ( t), in which the displacement occurs : v¯ =

x2 ≠ x1 = t2 ≠ t 1

x y

where x2 and x1 are the positions of the object at time t2 and t1 , respectively. The SI unit for velocity is m/s or ms≠1 .


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The average velocity can be positive or negative depending upon the sign of the displacement. It is zero if the displacement is zero. Fig(a) shows the x-t graphs for an object, moving with positive velocity, Fig(b) shows the x-t graphs for an object, moving with negative velocity, Fig(c) shows the x-t graphs for an object at rest.

Average speed It is defined as the total path length travelled divided by the total time interval during which the motion has taken place. Avergae speed =

T otal path length T otal time interval

Average speed has obviously the same unit (ms≠1 ) as that of velocity. But it does not tell us in what direction an object is moving. Thus, it is always positive.

Example:

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A car is moving along a straight line, say OP in Figure shown below. It moves from O to P in 18 s and returns from P to Q in 6 s. What is the average velocity and average speed of the car in going from O to P and back to Q ?

Answer: Average velocity =

Displacement +240m = T ime interval (18 + 6)s

Average velocity = +10ms≠1 Average speed =

T otal path length OP + P Q = T otal time interval t

Average speed =


(360 + 120)m = 20ms≠1 24s

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Acceleration Defined as the rate of change of velocity. SI unit is ms≠2 a=

3

v t

Motion in one dimension

It is also known as rectilinear or linear motion. A particle moving along a straight line is said to undergo one dimensional motion. In such a case, only one of the three rectangular coordinates changes with time.

Examples of one dimensional motion: • Motion of a train along a straight line.

• An object, like a ball, falling freely, vertically under gravity.

• The vertical up and down oscillations of an object suspended from a vertical spring.

kinematic equations The kinematic equations are a set of four equations that can be utilized to predict unknown information about an object’s motion if other information is known. The four kinematic equations that describe an object’s motion are: • d=v◊t+

1 2

◊ a ◊ t2

• Vf2 = Vi2 + 2 ◊ a ◊ d

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• V 2f = V i + a ◊ t • d=

vi +vf 2

◊t

There are a variety of symbols used in the above equations. Each symbol has its own specific meaning. The symbol d stands for the displacement of the object. The symbol t stands for the time for which the object moved. The symbol a stands for the acceleration of the object. And the symbol v stands for the velocity of the object; a subscript of i after the v (as in vi ) indicates that the velocity value is the initial velocity value and a subscript of f (as in vf ) indicates that the velocity value is the final velocity value.

Eample: Given is Vi = +30.00 ms≠1 , Vf = 0 ms≠1 , a = -8.00 ms≠2 . Find d.

Answer: Consider equation, Vf2 = Vi2 + 2 ◊ a ◊ d Substituting, (0m/s)2 = (30m/s)2 + 2 ◊ (≠8m/s2 ) ◊ d 16 ◊ d = 900 Therefore, d = 56.3m

4

Laws of motion

As per Aristotelian law of motion, a force is required to put a stationary body in motion or stop a moving body, and some external agency is needed to provide this force. The external agency may or may not be in contact with the body. Aristotelian law of motion is flawed, as per Galileo to get at the true law of nature for forces and motion, one has to imagine a world in which uniform motion is possible with no frictional forces opposing.


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Laws of inertia The law of inertia states that, body will preserve its velocity and direction so long as no force in its motion’s direction acts on it. For example,a package thrown out of an aeroplane will continue to move at the speed of the aeroplane on the horizontal axis (in the direction of the aeroplane movement). Since the law of gravity acts on the package (a vertical downward axis), the package will gather speed along the vertical axis, but on the horizontal axis its speed will remain equal to that of the aeroplane.

4.1

Newton first law of motion

First Law of motion states that,every body continues to be in its state of rest or of uniform motion in a straight line unless compelled by some external force to act otherwise.

4.2

Newton second law of motion

The first law refers to the simple case when the net external force on a body is zero. The second law of motion refers to the general situation when there is a net external force acting on the body. Second law of motion states that,The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction in which the force acts.

Momentum Momentum, P of a body is defined to be the product of its mass m and velocity v, and is denoted by p: p=m◊v Momentum is clearly a vector quantity. Say, under the action of a force F for time interval t, the velocity of a body of mass m changes from v to v + v i.e. its initial momentum p = m ◊ v changes by p = m v. According to the Second Law,

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Therefore,

F Ã

p Or F = K t F =

p t

dp dt

For a body of fixed mass m, dp d(mv) dv = =m = ma dt dt dt i.e the Second Law can also be written as F =k◊m◊a This shows that force is proportional to the product of mass m and acceleration a. For K = 1, F =m◊a

In SI unit force is one that causes an acceleration of 1 m s≠2 to a mass of 1 kg. This unit is known as newton : 1 N = 1 kg m s≠2 .

Example: The motion of a particle of mass m is described by y = ut + 12 gt2 . Find the force acting on the particle.


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Answer: Given,

1 y = ut + gt2 2

Now

V = acceleration, a= Therefore,

dy = u + gt dt dv =g dt

F orce F = ma = mg

Thus the given equation describes the motion of a particle under acceleration due to gravity and y is the position coordinate in the direction of g.

4.3

Newton third law of motion

Third law of motion states that,to every action there is always an equal and opposite reaction. • The terms action and reaction in the third law mean nothing else but force, using different terms for the same physical concept can sometimes be confusing. A simple and clear way of stating the third law is as follows : Forces always occur in pairs. Force on a body A by B is equal and opposite to the force on the body B by A. • The terms action and reaction in the third law may give a wrong impression that action comes before reaction i.e action is the cause and reaction the effect. There is no cause-effect relation implied in the third law. The force on A by B and the force on B by A act at the same instant. By the same reasoning, any one of them may be called action and the other reaction.

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• Action and reaction forces act on different bodies, not on the same body. Consider a pair of bodies A and B. According to the third law, FAB = ≠FBA

Conservation of momentum The total momentum of an isolated system of interacting particles is conserved. Consider two bodies A and B, with initial momenta pA and pB . The bodies collide, get apart, with final momenta pÕA and pÕB respectively. By the Second Law FAB t = pÕA ≠ pA Since, FAB = - FBA by third law;

Therefore,

FBA t = pÕB ≠ pB pÕA ≠ pA = ≠(pÕB ≠ pB ) pÕA + pÕB = pA + pB

which shows that the total final momentum of the isolated system equals its initial momentum.


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Work, energy and Power

Work The work done by the force is defined to be the product of component of the force in the direction of the displacement and the magnitude of this displacement. Consider a constant force F acting on an object of mass m. The object undergoes a displacement d in the positive x-direction as shown in Figure below:

Thus,

W = (F cos◊) d

Example: A cyclist comes to a skidding stop in 10 m. During this process, the force on the cycle due to the road is 200 N and is directly opposed to the motion. How much work does the road do on the cycle ?

Answer:

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Work done on the cycle by the road is the work done by the stopping (frictional) force on the cycle due to the road. The stopping force and the displacement make an angle of 1800 (fi rad) with each other. Thus, work done by the road, W = (F cos◊) d W = 200 ◊ 10 ◊ cosfi Therefore, work done = -200 J, It is this negative work that brings the cycle to a halt.

Kinetic energy The work done on a body that caused the body to be set in motion with some speed v can be expressed as function of the body’s final speed v and mass m, independent of type of force that acted on the body. We call this function the body’s Kinetic Energy. If an object of mass m has velocity v, its kinetic energy K is, 1 m v2 2 Kinetic energy is a scalar quantity. The kinetic energy of an object is a measure of the work an object can do by the virtue of its motion. K =

Work energy theorem The energy associated with the work done by the net force does not disappear after the net force is removed (or becomes zero), it is transformed into the Kinetic Energy of the body.This is called Work-Energy Theorem.

from newton’s second law

dK d 1 dv = ( mv 2 ) = m v dt dt 2 dt dK dx = Fv = F dt dt


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Thus, dK = Fdx. Integrating from the initial position (xi ) to final position (xf ), we have ⁄Kf

dK =

dx

xi

Ki

K f ≠ Ki =

⁄xf

⁄xf

F dx = W

xi

Thus, the WE theorem is proved for a variable force.

Potential energy Potential energy is the energy that an object has due to its position in a force field or that a system has due to the configuration of its parts. Gravitational potential energy of an object, as a function of the height h, is denoted by V(h) and it is the negative of work done by the gravitational force in raising the object to that height. V (h) = mgh

Power Power is defined as the time rate at which work is done or energy is transferred. The average power of a force is defined as the ratio of the work, W, to the total time t taken, Pa v =

W t

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Instantaneous power, P = dW dt The instantaneous power can also be expressed as:

dx = Fv dt Power, like work and energy, is a scalar quantity. Its dimensions are M L2 T≠ 3. In the SI, its unit is called a watt (W). P =F

Note: There is another unit of power, namely the horse-power (hp), 1 hp = 746 W.

6

Rotational motion

In uniform circular motion speed of the object is always constant and direction is changing. Thus, velocity of the object is changing and as a result object has acceleration. Angular velocity Angular velocity is defined as the change of the angular displacement in a unit of time. Angular velocity is symbolised with the Greek letter Ê omega. Average velocity= Circumference of the circle/time Ê = 2fi T = 2fif


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Angular acceleration Angular acceleration – is defined as the time rate of change of angular velocity.Thus, dÊ dt kinematic equations for rotational motion with uniform angular acceleration are: Ê = Ê0 + –t ◊ = ◊0 + Ê0 t + 12 –t2 Ê 2 = Ê02 + 2–(◊ ≠ ◊0 ) –=

Comparison transalation and rotational motion

7

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Gravitation

7.1

Kepler’s law

Kepler’s had given three law’s stated below. 1. Law of orbits : All planets move in elliptical orbits with the Sun situated at one of the foci of the ellipse.

2. Law of areas : The line that joins any planet to the sun sweeps equal areas in equal intervals of time. 3. Law of periods : The square of the time period of revolution of a planet is proportional to the cube of the semi-major axis of the ellipse traced out by the planet.


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Newton’s law of universal gravitation Newton’s law of universal gravitation states that any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. F =G

m1 m2 r2

Gravitational constant The gravitational constant, approximately 6.673 ◊ 10≠11 N.(m/kg)2 and denoted by letter G, is an empirical physical constant involved in the calculation(s) of gravitational force between two bodies. Note: • The escape speed from the surface of the Earth is Ve = earth.

Ô 2

2gRE ( = 11.2 Km/s) where RE is radius of

• If a particle is outside a uniform spherical shell or solid sphere with a spherically symmetric internal mass distribution, the sphere attracts the particle as though the mass of the sphere or shell were concentrated at the centre of the sphere. • If a particle is inside a uniform spherical shell, the gravitational force on the particle is zero. If a particle is inside a homogeneous solid sphere, the force on the particle acts toward the centre of the sphere. This force is exerted by the spherical mass interior to the particle. • A geostationary (geosynchronous communication) satellite moves in a circular orbit in the equatorial plane at a approximate distance of 4.22 ◊ 104 km from the Earthâ ès centre.

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8

Heat and Thermodynamics

Heat is the form of energy transferred between two (or more) systems or a system and its surroundings by virtue of temperature difference, here temperature is a relative measure, or indication of hotness or coldness.The SI unit of heat energy transferred is expressed in joule (J) while SI unit of temperature is kelvin (K), and 0 C. Relation ship between Fahrenheit temperature tF and Celsius temperature tC is given by tc tf ≠ 32 = 180 100 8.0.1

Ideal gas equation

As per ideal gas law P V = constant also, VT = constant. T heref ore,

PV T

should also be a constant.

PV = µR T Or,


P V = µRT

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Thermal expansion

A change in the temperature of a body causes change in its dimensions. The increase in the dimensions of a body due to the increase in its temperature is called thermal expansion. The expansion in length is called linear expansion. The expansion in area is called area expansion. The expansion in volume is called volume expansion.

If the substance is in the form of a long rod, then for small change in temperature, ” T, the fractional change in length, ” l/l, is directly proportional to ” T.

shop.ssb cra ck.com l

= –1 T l where –1 is known as the coefficient of linear expansion and is characteristic of the material of the rod. Similarly, we consider the fractional change VV of a substance for temperature change T and define the coefficient of volume expansion –v , as –v = (

V 1 ) V T

Note For ideal gas –v =

8.1

1 T

. At , 0 C –v = 3.7 ◊ 10≠3 K ≠1 , which is much larger than that for solids and liquids.

Specific heat capacity

The change in temperature of a substance, when a given quantity of heat is absorbed or rejected by it, is characterised by a quantity called the heat capacity of that substance. We define heat capacity, S of a substance as Q T Where, Q is the amount of heat supplied to the substance to change its temperature from T to T + T . The specific heat capacity is the property of the substance which determines the change in the temperature of the substance (undergoing no phase change) when a given quantity of heat is absorbed (or rejected) by it. It is defined as the amount of heat per unit mass absorbed or rejected by the substance to change its temperature by one unit. It depends on the nature of the substance and its temperature. The SI unit of specific heat capacity is Jkg ≠1 K ≠1 . S=


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If Q stands for the amount of heat absorbed or rejected by a substance of mass m when it undergoes a temperature change T, then the specific heat capacity s, of that substance is given by, s=

S 1 = M m

Q T

Notes: • The latent heat of fusion is the heat per unit mass required to change a substance from solid into liquid at the same temperature and pressure. The latent heat of vaporisation is the heat per unit mass required to change a substance from liquid to the vapour state without change in the temperature and pressure. • The three modes of heat transfer are conduction, convection and radiation.

• Newton’s Law of Cooling says that the rate of cooling of a body is proportional to the excess temperature of the body over the surroundings : dQ = ≠K(T2 ≠ T1 ) dt Where T1 is the temperature of the surrounding medium and T2 is the temperature of the body.

8.2

Thermodynamics

• The zeroth law of thermodynamics states that â Ÿtwo systems in thermal equilibrium with a third system are in thermal equilibrium with each otherâ è. The Zeroth Law leads to the concept of temperature. • he first law of thermodynamics is the general law of conservation of energy applied to any system in which energy transfer from or to the surroundings (through heat and work) is taken into account. It states that, Q= U+ W

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Where Q is the heat supplied to the system, change in internal energy of the system.

W is the work done by the system and

U is the

• Equilibrium states of a thermodynamic system are described by state variables. The value of a state variable depends only on the particular state, not on the path used to arrive at that state. Examples of state variables are pressure (P ), volume (V ), temperature (T ), and mass (m ). Heat and work are not state variables. An Equation of State (like the ideal gas equation P V = µRT ) is a relation connecting different state variables. • In an isothermal expansion of an ideal gas from volume V 1 to V 2 at temperature T the heat absorbed (Q) equals the work done (W ) by the gas, each given by Q = W = µRT ln(

V2 ) V1

• The second law of thermodynamics disallows some processes consistent with the First Law of Thermodynamics. It states Kelvin ≠ P lanck statement

No process is possible whose sole result is the absorption of heat from a reservoir and complete conversion of the heat into work. Clausius statement No process is possible whose sole result is the transfer of heat from a colder object to a hotter object. Put simply, the Second Law implies that no heat engine can have efficiency ÷ equal to 1 or no refrigerator can have co-efficient of performance – equal to infinity.


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• Carnot engine is a reversible engine operating between two temperatures T 1 (source) and T 2 (sink). The Carnot cycle consists of two isothermal processes connected by two adiabatic processes. The efficiency of a Carnot engine is given by ÷ =1≠

T2 T1

No engine operating between two temperatures can have efficiency greater than that of the Carnot engine. • If Q > 0, heat is added to the system; If Q < 0, heat is removed to the system; If W > 0, Work is done by the system; If W < 0, Work is done on the system.

8.3

Electrostatics

1. Conductors allow movement of electric charge through them, insulators do not. In metals, the mobile charges are electrons; in electrolytes both positive and negative ions are mobile. 2. Electric charge has three basic properties: quantisation, additivity and conservation. Quantisation of electric charge means that total charge (q) of a body is always an integral multiple of a basic quantum of charge (e) i.e., q = n e, where n = 0, ±1, ±2, ±3, .... Proton and electron have charges +e, -e, respectively. For macroscopic charges for which n is a very large number, quantisation of charge can be ignored. Additivity of electric charges means that the total charge of a system is the algebraic sum (i.e., the sum taking into account proper signs) of all individual charges in the system. Conservation of electric charges means that the total charge of an isolated system remains unchanged with time. This means that when bodies are charged through friction, there is a transfer of electric charge from one body to another, but no creation or destruction of charge.

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3. Coulomb’s Law: The mutual electrostatic force between two point charges q1 and q2 is proportional to the product q1 q2 and inversely proportional to the square of the distance r21 separating them. Mathematically, F21 = f orce on q2 due to q1 =

k(q1 q2 ) rˆ21 r2 12

where rˆ21 is a unit vector in the direction from q1 to q2 and k = 4fi1Á0 is the constant of proportionality. In SI units, the unit of charge is coulomb. The experimental value of the constant Á0 is 8.854 ◊ 10≠12 C 2 N ≠1 m≠2 The approximate value of k is 9 ◊ 109 N m2 C ≠2

The ratio of electric force and gravitational force between a proton and an electron is

ke2 Gme mp

¥ 2.3◊1039

4. Superposition Principle: The principle is based on the property that the forces with which two charges attract or repel each other are not affected by the presence of a third (or more) additional charge(s). For an assembly of charges q1 , q2 , q3 , ..., the force on any charge, say q1 , is the vector sum of the force on q1 due to q2 , the force on q1 due to q3 , and so on. For each pair, the force is given by the Coulomb’s law for two charges stated earlier. 5. An electric field line is a curve drawn in such a way that the tangent at each point on the curve gives the direction of electric field at that point. The relative closeness of field lines indicates the relative strength of electric field at different points; they crowd near each other in regions of strong electric field and are far apart where the electric field is weak. In regions of constant electric field, the field lines are uniformly spaced parallel straight lines. Some of the important properties of field lines are: (i) Field lines are continuous curves without any breaks. (ii) Two field lines cannot cross each other. (iii) Electrostatic field lines start at positive charges and end at negative charges -they cannot form closed loops. 6. An electric dipole is a pair of equal and opposite charges q and -q separated by some distance 2a. Its dipole moment vector p has magnitude 2qa and is in the direction of the dipole axis from -q to q.


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7. Field of an electric dipole in its equatorial plane (i.e., the plane perpendicular to its axis and passing through its centre) at a distance r from the centre: E=

≠p 1 ≠p ¥ f or r >> a 4fiÁ0 (a2 + r2 ) 23 4fiÁ0 r3

Dipole electric field on the axis at a distance r from the centre: E=

2p 2pr ¥ f or r >> a 4fiÁ0 (r2 ≠ a2 )2 4fiÁ0 r3

8. In a uniform electric field E, a dipole experiences a torque · given by · =p◊E but experiences no net force. 9. The flux

„ of electric field E through a small area element

S is given by

„=E s 10. Gauss’s law: The flux of electric field through any closed surface S is Á10 times the total charge enclosed by S. The law is especially useful in determining electric field E, when the source distribution has simple symmetry: • Thin infinitely long straight wire of uniform linear charge density ⁄ ⁄ n ˆ 2fiÁ0 r

E=

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where r is the perpendicular distance of the point from the wire and n ˆ is the radial unit vector in the plane normal to the wire passing through the point. • Infinite thin plane sheet of uniform surface charge density ‡ E=

‡ n ˆ 2Á0 r

where n ˆ is a unit vector normal to the plane, outward on either side. • Thin spherical shell of uniform surface charge density ‡ E=

q rˆ2 4fiÁ0 r2

E=0

;

(r Ø R) (r < R)

where r is the distance of the point from the centre of the shell and R the radius of the shell. q is the total charge of the shell: q = 4fiR2 2‡. The electric field outside the shell is as though the total charge is concentrated at the centre. The same result is true for a solid sphere of uniform volume charge density. The field is zero at all points inside the shell. 11. Electrostatic force is a conservative force. Work done by an external force (equal and opposite to the electrostatic force) in bringing a charge q from a point R to a point P is VP ≠VR , which is the difference in potential energy of charge q between the final and initial points. 12. For series-connected capacitors the equivalent capacitance can be expressed as 1/C = 1/C1 + 1/C2 + .. + 1/Cn . For parallel-connected capacitors the equivalent capacitance can be expressed as C = C1 + C2 + .. + Cn


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8.4

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Electric current

In a given time interval t, let q + be the net amount (i.e., forward minus backward) of positive charge that flows in the forward direction across the area. Similarly, let q- be the net amount of negative charge flowing across the area in the forward direction. The net amount of charge flowing across the area in the forward direction in the time interval t, then, is q = q+ - q- . This is proportional to t for steady current is defined to be the current across the area in the forward direction. (If it turn out to be a negative number, it implies a current in the backward direction.) 8.4.1

Ohm’s law

Imagine a conductor through which a current I is flowing and let V be the potential difference between the ends of the conductor. Then Ohmâ ès law states that V ÃI

or,

V = RI

where the constant of proportionality R is called the resistance of the conductor. The SI units of resistance is ohm, and is denoted by the symbol Ê. l A Here, l is the length of the conductor, A is the cross sectional area of the conductor and fl is resistivity. R=fl

note: Current per unit area (taken normal to the current), I/A, is called current density and is denoted by j. The SI units of the current density are A/m2 .

Mobility

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The mobility m defined as the magnitude of the drift velocity per unit electric field. ST unit of mobility is m2 /V s

Resistance colour code


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Resistance temperature dependence The resistivity of a material is found to be dependent on the temperature. The resistivity of a metallic conductor is approximately given by, rT = r0 [1 + –(T ≠ T0 )]

where rT the resistivity at a temperature T and r0 is the same at a reference temperature T0 . – is called the temperature co-efficient of resistivity, its dimension is (T ≠1 ).

Resistors- series and parallel Series circuits are sometimes called current-coupled or daisy chain-coupled. The current in a series circuit goes through every component in the circuit. Therefore, all of the components in a series connection carry the same current. There is only one path in a series circuit in which the current can flow. • Series Current I = I1 = I2 = .......In

In a series circuit the current is the same for all elements.

• Series Resistors The total resistance of resistors in series is equal to the sum of their individual resistances:

Rtotal = R1 + R2 + .... + Rn

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Electrical conductance presents a reciprocal quantity to resistance. Total conductance of a series circuits of pure resistors, therefore, can be calculated from the following expression: 1 1 1 1 = + + .... + Gtotal G1 G2 Gn If two or more components are connected in parallel they have the same potential difference (voltage) across their ends. The potential differences across the components are the same in magnitude, and they also have identical polarities. The same voltage is applicable to all circuit components connected in parallel. The total current is the sum of the currents through the individual components, in accordance with Kirchhoff’s current law. • Voltage In a parallel circuit the voltage is the same for all elements. V = V1 = V2 = ... = Vn • Resistors The current in each individual resistor is found by Ohm’s law. Factoring out the voltage gives It otal = V (

1 1 1 + + .... + ) R1 R2 Rn

To find the total resistance of all components, add the reciprocals of the resistances of each component and take the reciprocal of the sum. Total resistance will always be less than the value of the smallest resistance:


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1 Rtotal

=

1 1 1 + + .... + R1 R2 Rn

Kirchhoff’s rule • Junction rule: At any junction, the sum of the currents entering the junction is equal to the sum of currents leaving the junction. • Loop rule: The algebraic sum of changes in potential around any closed loop involving resistors and cells in the loop is zero.

Magnetic Effect of Currents Let us suppose that there is a point charge q (moving with a velocity v and, located at r at a given time t) in presence of both the electric field E (r) and the magnetic field B (r). The force on an electric charge q due to both of them can be written as F = q[E(r) + v ◊ B(r)] = Felectric + Fmagnetic If we look at the interaction with the magnetic field, we find the following features:

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• It depends on q, v and B (charge of the particle, the velocity and the magnetic field). Force on a negative charge is opposite to that on a positive charge. • The magnetic force q[v◊B] includes a vector product of velocity and magnetic field. The vector product makes the force due to magnetic field vanish (become zero) if velocity and magnetic field are parallel or anti-parallel. The force acts in a (sideways) direction perpendicular to both the velocity and the magnetic field. Its direction is given by the screw rule or right hand rule for vector (or cross) product.

• The magnetic force is zero if charge is not moving (as then | v |= 0). Only a moving charge feels the magnetic force.

Magnetic force on a current-carrying conductor Consider a rod of a uniform cross-sectional area A and length l. We shall assume one kind of mobile carriers as in a conductor (here electrons). Let the number density of these mobile charge carriers in it be n. Then the total number of mobile charge carriers in it is nAl. For a steady current I in this conducting rod, we may assume that each mobile carrier has an average drift velocity vd . In the presence of an external magnetic field B, the force on these carriers is: F = (nAl)qvd ◊ B Engineering Knowledge Test

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Biot-savart law Consider an infinitesimal element dl of the conductor. The magnetic field dB due to this element is to be determined at a point P which is at a distance r from it. Let ◊ be the angle between dl and the displacement vector r. According to Biot-Savart’s law, the magnitude of the magnetic field dB is proportional to the current I, the element length | dl |, and inversely proportional to the square of the distance r. Its direction is perpendicular

to the plane containing dl and r . Thus, in vector notation

The magnitude of this field is,

dB Ã

Idl ◊ r µ0 idl ◊ r = r3 4fi r3

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µ0 Idlsin◊r 4fi r3 The proportionality constant in SI units has the exact value, dB =

µ0 = 10≠7 T m/A 4fi

Ampere’s circuital law The surface has current passing through it. We consider the boundary to be made up of a number of small line elements. Consider one such element of length dl. We take the value of the tangential component of the magnetic field, Bt , at this element and multiply it by the length of that element dl [Note: Bt dl = B.dl]. All such products are added together. We consider the limit as the lengths of elements get smaller and their number gets larger. The sum then tends to an integral. Ampereâ ès law states that this integral is equal to µ0 times the total current passing through the surface, i.e., j B.dl = µ0 I


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Solenoid and Toroid Solenoid consists of a long wire wound in the form of a helix where the neighbouring turns are closely spaced. So each turn can be regarded as a circular loop. The net magnetic field is the vector sum of the fields due to all the turns. Enamelled wires are used for winding so that turns are insulated from each other.

Consider a rectangular Amperian loop abcd. Along cd the field is zero as argued above. Along transverse sections bc and ad, the field component is zero. Thus, these two sections make no contribution. Let the field along ab be B. Thus, the relevant length of the Amperian loop is, L = h. Let n be the number of turns per unit length, then the total number of turns is nh. The enclosed current is, Ie = I(nh), where I is the current in the solenoid. From Ampereâ ès circuital law BL = µ0 Ie , Bh = µ0 I(nh) Therefore, B = µ0 nI

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The toroid is a hollow circular ring on which a large number of turns of a wire are closely wound. It can be viewed as a solenoid which has been bent into a circular shape to close on itself. It is shown in Figure below carrying a current I. We shall see that the magnetic field in the open space inside (point P) and exterior to the toroid (point Q) is zero. The field B inside the toroid is constant in magnitude for the ideal toroid of closely wound turns.

Let r be the average radius of the toroid and n be the number of turns per unit length. Then B=

and thus,

µN I 2fir

N = 2firn = (average)perimeterof thetoroid ◊ numberof turnsperunitlength


B = µ0 nI

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8.5

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Magnetism and gauss law

Consider a small vector area element S of a closed surface S as in figure above. The magnetic flux through S is defined as „B = B. S, where B is the field at S. We divide S into many small area elements and calculate the individual flux through each. Then, the net flux „B is, „B =

„B = B. S = 0

By Gauss law we get, E. S =

q Á0

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, where q is the electric charge enclosed by the surface.

8.6

Electromagnetic induction

Faraday’s law of induction The magnitude of the induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit. d„B dt In the case of a closely wound coil of N turns, change of flux associated with each turn, is the same. Therefore, the expression for the total induced emf is given by Á=≠

Á = ≠N

d„B dt

Lenz’s law The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it.


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Suppose that the induced current was in the direction opposite to the one depicted in figure above. In that case, the South-pole due to the induced current will face the approaching North-pole of the magnet. The bar magnet will then be attracted towards the coil at an ever increasing acceleration. A gentle push on the magnet will initiate the process and its velocity and kinetic energy will continuously increase without expending any energy. If this can happen, one could construct a perpetual-motion machine by a suitable arrangement. This violates the law of conservation of energy and hence can not happen. Now consider the correct case shown in figure above. In this situation, the bar magnet experiences a repulsive force due to the induced current. Therefore, a person has to do work in moving the magnet. Electromotive force

Emf is the work done per unit charge,

shop.ssb cra ck.com Á=

w = Blv q

Eddy currents When bulk pieces of conductors are subjected to changing magnetic flux, induced currents are produced in them. However, their flow patterns resemble swirling eddies in water. This effect was discovered by physicist Foucault (1819-1868) and these currents are called eddy currents. Applications: • Magnetic braking in trains. • Electromagnetic damping. • Induction furnace.

• Electric power meters.

Induction An electric current can be induced in a coil by flux change produced by another coil in its vicinity or flux change produced by the same coil. These two situations are described separately in the next two sub-sections. However, in both the cases, the flux through a coil is proportional to the current. That is „b Ã I. Further, if the geometry of the coil does not vary with time then, d„B dI dt = dt For a closely wound coil of N turns, the same magnetic flux is linked with all the turns. When the flux „B through the coil changes, each turn contributes to the induced emf. Therefore, N „B Ã I


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Mutual inductance

We denote the radius of the inner solenoid S1 by r1 and the number of turns per unit length by n1 . The corresponding quantities for the outer solenoid S2 are r2 and n2 , respectively. Let N1 andN2 be the total number of turns of coils S1 and S2 , respectively. When a current I2 is set up through S2 , it in turn sets up a magnetic flux through S1 . Let us denote it by phi1 . The corresponding flux linkage with solenoid S1 is, N1 „1 = M12 I2 M12 is called the mutual inductance of solenoid S1 with respect to solenoid S2 . It is also referred to as the coefficient of mutual induction. For these simple co-axial solenoids it is possible to calculate M12 . The magnetic field due to the current I2 in S2 is µ0 n2 I2 . The resulting flux linkage with coil S1 is,

shop.ssb cra ck.com N1 „1 = (n1 l)(fir12 )(µ0 n2 I2 )

where n1 l is the total number of turns in solenoid S1 . Thus, M12 = µ0 n1 n2 fir12 I2 similarly, M21 = µ0 n1 n2 fir12 I2 Therefore, M12 = M21 = M Note: 2 Á1 = ≠M dI dt , It shows that varying current in a coil can induce emf in a neighbouring coil. The magnitude of the induced emf depends upon the rate of change of current and mutual inductance of the two coils.

8.7

Alternating current

• An alternating voltage v = vm sinÊt applied to a resistor R drives a current i = im sinÊt in the resistor, im = vRm . The current is in phase with the applied voltage. • For an alternating current i = im sinÊt passing through a resistor R, the average power loss P (averaged over a cycle) due to joule heating is ( 12 )i2m R. To express it in the same form as the dc power (P = I 2 R), a special value of current is used. It is called root mean square (rms) current and is denoted by I:


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im i= Ô = 0.707im 2 2 Similarly, the rms voltage is defined by vm v= Ô = 0.707vm 2 2 • An ac voltage v = vm sinÊt applied to a pure inductor L, drives a current in the inductor i = im sin(Êt≠ vm fi 2 ), where im = XL . XL = ÊL is called inductive reactance. The current in the inductor lags the voltage by fi/2. The average power supplied to an inductor over one complete cycle is zero. • An ac voltage v = vm sinÊt applied to a pure inductor L, drives a current in the inductor i = im sin(Êt+ fi 2 ). Here, im =

vm Xc ,

Xc =

1 ÊC

is called capacitive reactance.

The current through the capacitor is fi/2 ahead of the applied voltage. As in the case of inductor, the average power supplied to a capacitor over one complete cycle is zero. • In a purely inductive or capacitive circuit, cos„ = 0 and no power is dissipated even though a current is flowing in the circuit. In such cases, current is referred to as a wattless current. • The phase relationship between current and voltage in an ac circuit can be shown conveniently by representing voltage and current by rotating vectors called phasors. A phasor is a vector which rotates about the origin with angular speed Ê . The magnitude of a phasor represents the amplitude or peak value of the quantity (voltage or current) represented by the phasor. • An interesting characteristic of a series RLC circuit is the phenomenon of resonance. The circuit 1 exhibits resonance, i.e., the amplitude of the current is maximum at the resonant frequency, Ê0 = ÔLC .

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0L The quality factor Q defined by Q = ÊR = Ê01CR is an indicator of the sharpness of the resonance, the higher value of Q indicating sharper peak in the current.

9 9.1

ELECTROMAGNETIC WAVES ELECTROMAGNETIC SPECTRUM

At the time Maxwell predicted the existence of electromagnetic waves, the only familiar electromagnetic waves were the visible light waves. The existence of ultraviolet and infrared waves was barely established. By the end of the nineteenth century, X-rays and gamma rays had also been discovered. We now know that, electromagnetic waves include visible light waves, X-rays, gamma rays, radio waves, microwaves, ultraviolet and infrared waves. The classification of em waves according to frequency is the electromagnetic spectrum


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9.2

Radio waves

Radio waves are produced by the accelerated motion of charges in conducting wires. They are used in radio and television communication systems. They are generally in the frequency range from 500 kHz to about 1000 MHz. The AM (amplitude modulated) band is from 530 kHz to 1710 kHz. Higher frequencies upto 54 MHz are used for short wave bands. TV waves range from 54 MHz to 890 MHz. The FM (frequency modulated) radio band extends from 88 MHz to 108 MHz. Cellular phones use radio waves to transmit voice communication in the ultra high frequency (UHF) band.

9.3

Microwaves

Microwaves (short-wavelength radio waves), with frequencies in the gigahertz (GHz) range, are produced by special vacuum tubes (called klystrons, magnetrons and Gunn diodes). Due to their short wavelengths, they are suitable for the radar systems used in aircraft navigation. Radar also provides the basis for the speed guns used to time fast balls, tennisserves, and automobiles. Microwave ovens are an interesting domestic


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application of these waves. In such ovens, the frequency of the microwaves is selected to match the resonant frequency of water molecules so that energy from the waves is transferred efficiently to the kinetic energy of the molecules. This raises the temperature of any food containing water

9.4

Infrared waves

Infrared waves are produced by hot bodies and molecules. This band lies adjacent to the low-frequency or long-wave length end of the visible spectrum. Infrared waves are sometimes referred to as heat waves. This is because water molecules present in most materials readily absorb infrared waves (many other molecules, for example, CO2 , N H3 , also absorb infrared waves). After absorption, their thermal motion increases, that is, they heat up and heat their surroundings. Infrared lamps are used in physical therapy. Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the greenhouse effect. Incoming visible light (which passes relatively easily through the atmosphere) is absorbed by the earth’s surface and reradiated as infrared (longer wavelength) radiations.

9.5

Visible Rays

It is the most familiar form of electromagnetic waves. It is the part of the spectrum that is detected by the human eye. It runs from about 4 ◊ 1014 Hz to about 7 ◊ 1014 Hz or a wavelength range of about 700 - 400 nm. Visible light emitted or reflected from objects around us provides us information about the world. Our eyes are sensitive to this range of wavelengths. Different animals are sensitive to different range of wavelengths. For example, snakes can detect infrared waves, and the ’visible’ range of many insects extends well into the utraviolet.

9.6

Ultraviolet rays

It covers wavelengths ranging from about 4◊10≠7 m (400 nm) down to 6◊10≠10 m (0.6 nm). Ultraviolet (UV) radiation is produced by special lamps and very hot bodies. The sun is an important source of ultraviolet light. But fortunately, most of it is absorbed in the ozone layer in the atmosphere at an altitude of about 40-50 km. UV light in large quantities has harmful effects on humans. Exposure to UV radiation induces the production of more melanin, causing tanning of the skin. UV radiation is absorbed by ordinary glass. Hence, one cannot get tanned or sunburn through glass windows.

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9.7

X-rays

Beyond the UV region of the electromagnetic spectrum lies the X-ray region. We are familiar with X-rays because of its medical applications. It covers wavelengths from about 10≠8 m (10 nm) down to 10≠13 m (10≠4 nm). One common way to generate X-rays is to bombard a metal target by high energy electrons. X-rays are used as a diagnostic tool in medicine and as a treatment for certain forms of cancer. Because X-rays damage or destroy living tissues and organisms, care must be taken to avoid unnecessary or over exposure.

9.8

Gamma rays

They lie in the upper frequency range of the electromagnetic spectrum and have wavelengths of from about 10≠10 m to less than 10≠14 m. This high frequency radiation is produced in nuclear reactions and also emitted by radioactive nuclei. They are used in medicine to destroy cancer cells.

10

RAY OPTICS AND OPTICAL INSTRUMENTS

• Nature has endowed the human eye (retina) with the sensitivity to detect electromagnetic waves within a small range of the electromagnetic spectrum. Electromagnetic radiation belonging to this region of the spectrum (wavelength of about 400 nm to 750 nm) is called light. It is mainly through light and the sense of vision that we know and interpret the world around us. • There are two things that we can intuitively mention about light from common experience. First, that it travels with enormous speed and second, that it travels in a straight line. It took some time for people to realise that the speed of light is finite and measurable. Its presently accepted value in vacuum is


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c = 2.99792458 ◊ 108 ms≠1 . For many purposes, it suffices to take c = 3 ◊ 108 ms≠1 . The speed of light in vacuum is the highest speed attainable in nature.

10.1

REFRACTION

When a beam of light encounters another transparent medium, a part of light gets reflected back into the first medium while the rest enters the other. A ray of light represents a beam. The direction of propagation of an obliquely incident ray of light that enters the other medium, changes at the interface of the two media. This phenomenon is called refraction of light. Snell experimentally obtained the following laws of refraction: • The incident ray, the refracted ray and the normal to the interface at the point of incidence, all lie in the same plane. • The ratio of the sine of the angle of incidence to the sine of angle of refraction is constant. Remember that the angles of incidence (i ) and refraction (r ) are the angles that the incident and its refracted ray make with the normal, respectively. We have

where n21

sin i = n21 sin r is a constant, called the refractive index of the second medium with respect to the first medium.

Note: Optical density should not be confused with mass density, which is mass per unit volume. It is possible that mass density of an optically denser medium may be less than that of an optically rarer medium (optical density is the ratio of the speed of light in two media). For example, turpentine and water. Mass density of turpentine is less than that of water but its optical density is higher.

10.2

TOTAL INTERNAL REFLECTION

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When light travels from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted to the second medium. This reflection is called the internal reflection.

10.3

Total internal reflection in nature

• Mirage:

On hot summer days, the air near the ground becomes hotter than the air at higher levels. The refractive index of air increases with its density. Hotter air is less dense, and has smaller refractive index than the cooler air. If the air currents are small, that is, the air is still, the optical density at different layers of air increases with height. As a result, light from a tall object such as a tree, passes through a medium whose refractive index decreases towards the ground. Thus, a ray of light from such an object successively bends away from the normal and undergoes total internal reflection, if the angle of incidence for the air near the ground exceeds the critical angle.

• Diamond:

Diamonds are known for their spectacular brilliance. Their brilliance is mainly due to the total internal reflection of light inside them. The critical angle for diamond-air interface ( 24.4o ) is very small, therefore once light enters a diamond, it is very likely to undergo total internal reflection inside it. Diamonds found in nature rarely exhibit the brilliance for which they are known. It is the technical skill of a diamond cutter which makes diamonds to sparkle so brilliantly. By cutting the diamond suitably, multiple total internal reflections can be made to occur

• Prism:

Prisms designed to bend light by 90o or by 180o make use of total internal reflection

• Optical fibres

Now-a-days optical fibres are extensively used for transmitting audio and video signals through long distances. Optical fibres too make use of the phenomenon of total internal reflection. Optical fibres are


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fabricated with high quality composite glass/quartz fibres. Each fibre consists of a core and cladding. The refractive index of the material of the core is higher than that of the cladding. When a signal in the form of light is directed at one end of the fibre at a suitable angle, it undergoes repeated total internal reflections along the length of the fibre and finally comes out at the other end . Since light undergoes total internal reflection at each stage, there is no appreciable loss in the intensity of the light signal.

10.4

Power of a lens

Optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device: P = 1/f. High optical power corresponds to short focal length. The SI unit for optical power is the inverse metre (m≠1 ), which is commonly called the dioptre.

10.5

DISPERSION BY A PRISM

It has been known for a long time that when a narrow beam of sunlight, usually called white light, is incident on a glass prism, the emergent light is seen to be consisting of several colours. There is actually a continuous variation of colour, but broadly, the different component colours that appear in sequence are: violet, indigo, blue, green, yellow, orange and red (given by the acronym VIBGYOR). The red light bends the least, while the violet light bends the most. The phenomenon of splitting of light into its component colours is known as dispersion.

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11

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OPTICAL INSTRUMENTS

• Eye

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Light enters the eye through a curved front surface, the cornea. It passes through the pupil which is the central hole in the iris. The size of the pupil can change under control of muscles. The light is further focussed by the eye lens on the retina. The retina is a film of nerve fibres covering the curved back surface of the eye. The retina contains rods and cones which sense light intensity and colour, respectively, and transmit electrical signals via the optic nerve to the brain which finally processes this information. The shape (curvature) and therefore the focal length of the lens can be modified somewhat by the ciliary muscles. For example, when the muscle is relaxed, the focal length is about 2.5 cm and objects at infinity are in sharp focus on the retina. When the object is brought closer to the eye, in order to maintain the same image-lens distance (â 2.5 cm), the focal length of the eye lens becomes shorter by the action of the ciliary muscles. This property of the eye is called accommodation. If the object is too close to the eye, the lens cannot curve enough to focus the image on to the retina, and the image is blurred. • The closest distance for which the lens can focus light on the retina is called the least distance of distinct vision, or the near point. The standard value for normal vision is taken as 25 cm. (Often the near point is given the symbol D.) This distance increases with age, because of the decreasing effectiveness of the ciliary muscle and the loss of flexibility of the lens. • The near point may be as close as about 7 to 8 cm in a child ten years of age, and may increase to as much as 200 cm at 60 years of age. Thus, if an elderly person tries to read a book at about 25 cm from the eye, the image appears blurred. This condition (defect of the eye) is called presbyopia. It is corrected by using a converging lens for reading. Thus, our eyes are marvellous organs that have the capability to interpret incoming electromagnetic waves as images through a complex process. These are our greatest assets and we must take proper care to protect them. Imagine the world without a pair of functional eyes. Yet many amongst us bravely face this challenge by effectively overcoming their limitations to lead a normal life. They deserve our appreciation for their courage and conviction. • In spite of all precautions and proactive action, our eyes may develop some defects due to various Engineering Knowledge Test

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reasons. We shall restrict our discussion to some common optical defects of the eye. For example, the light from a distant object arriving at the eye-lens may get converged at a point in front of the retina. This type of defect is called nearsightedness or myopia. • if the eye-lens focusses the incoming light at a point behind the retina, a convergent lens is needed to compensate for the defect in vision. This defect is called farsightedness or hypermetropia

11.1

The microscope

A simple magnifier or microscope is a converging lens of small focal length. In order to use such a lens as a microscope, the lens is held near the object, one focal length away or less, and the eye is positioned close to the lens on the other side. The idea is to get an erect, magnified and virtual image of the object at a distance so that it can be viewed comfortably, i.e., at 25 cm or more. If the object is at a distance f, the image is at infinity. However, if the object is at a distance slightly less than the focal length of the lens, the image is virtual and closer than infinity. Although the closest comfortable distance for viewing the image is when it is at the near point (distance D = 25 cm), it causes some strain on the eye. Therefore, the image formed at infinity is often considered most suitable for viewing by the relaxed eye.

11.2

Telescope

The telescope is used to provide angular magnification of distant objects. It also has an objective and an eyepiece. But here, the objective has a large focal length and a much larger aperture than the eyepiece. Light from a distant object enters the objective and a real image is formed in the tube at its second focal point. The eyepiece magnifies this image producing a final inverted image.

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Engineering Physics


'

Engineering'Physics'MCQs'

Engineering'Physics'MCQs' ! 1.'''Mirage'is'due'to' (a)' unequal'heating'of'different'parts' (b)' magnetic'disturbances'in'the' of'the'atmosphere' atmosphere' (c)' depletion'of'ozone'layer'in'the' (d)' equal'heating'of'different'parts'of'the' atmosphere' atmosphere' 2.'''Metals'are'good'conductors'of'electricity'because' (a)' they'contain'free'electrons' (b)' the'atoms'are'lightly'packed' (c)' they'have'high'melting'point' (d)' all'of'the'above' ' 3.'''Pick'out'the'scalar'quantity' (a)' force' (b)' pressure' (c)' velocity' (d)' acceleration' ' 4.'''Sound'waves'in'air'are' (a)' transverse' (b)' longitudinal' (c)' electromagnetic' (d)' Polarized'' ' 5.'''Lux'is'the'SI'unit'of' (a)' intensity'of'illumination' (b)' luminous'efficiency' (c)' luminous'flux' (d)' luminous'intensity' ' 6.'''It'takes'much'longer'to'cook'food'in'the'hills'than'in'the'plains,'because' (a)' in' the' hills' the' atmospheric' (b)' due' to' low' atmospheric' pressure' on' pressure'is'lower'than'that'in'the' the' hills,' the' water' boils' at' a' plains' and' therefore' water' boils' temperature' higher' than' 100oC' and' at' a' temperature' lower' than' therefore'water'takes'longer'to'boil' 100oC' causing' an' increase' in' ' cooking'time' (c)' in' the' hills' the' atmospheric' (d)' in' the' hills' the' humidity' is' high' and' density' is' low' and' therefore' a' lot' therefore'a'lot'of'heat'is'absorbed'by' of'heat'is'lost'to'the'atmosphere' the' atmosphere' leaving' very' little' heat'for'cooking' ' 7.'''Moment'of'inertia'is' (a)' vector' (b)' scalar' (c)' phasor' (d)' tensor' ' 8.'''Sound'travels'at'the'fastest'speed'in'


(a)' steel' (c)' air' ' 9.'''Railway'tracks'are'banked'on'curves' (a)' necessary' centrifugal' force' may' be' obtained' from' the' horizontal' component'weight'of'the'train' (c)' necessary' centripetal' force' may' be' obtained' from' the' horizontal' component' of' the' weight' of' the' train' ' 10.''Optical'fibre'works'on'the' (a)' principle'of'refraction' (c)' scattering' ' 11.'Rainbow'is'due'to' (a)' absorption'of'sunlight'in'minute' water'droplets' (c)' ionisation'of'water'deposits'

'


(b)' water' (d)' vacuum' (b)' to'avoid'frictional'force'between'the' tracks'and'wheels' (d)' the'train'may'not'fly'off'in'the' opposite'direction'

(b)' total'internal'reflection' (d)' interference' (b)' diffusion'of'sunlight'through'water' droplets' (d)' refraction'and'reflection'of'sunlight' by'water'droplets'

12.'Isotopes'of'an'element'contain' (a)' the'same'number'of'protons'but' (b)' the'same'number'of'neutrons'but' different'number'of'neutrons' different'number'of'protons' (c)' equal'number'of'protons'and' (d)' equal'number'of'nucleons' electrons' ' 13.'One'wattUhour'is'equivalent'to' (a)' 6.3'x'103'J' (b)' 6.3'x'10U7'J' (c)' 3.6'x'103'J' (d)' 3.6'x'10U3'J' ' 14.'Identify'the'vector'quantity'from'the'following' (a)' Heat' (b)' Angular'momentum' (c)' Time' (d)' Work' ' 15.''In'a'region,'steady'and'uniform'electric'and'magnetic'fields'are'present.'These'two' fields'are'parallel'to'each'other.'A'charged'particle'is'released'from'rest'in'this'region.' The'path'of'the'particle'will'be'a' (a)' circle' (b)' helix' (c)' straight'line' (d)' ellipse'


'


' 16.'Heat'energy'received'by'the'earth'from'the'sun'is'due'to'(CPMT'1994)' (a)' Convection' (b)' Radiation' (c)' )'Reflection'of'light' (d)' Transmission'of'light' ' 17.'Spectrum'of'a'perfectly'black'body'is' (a)' Line'spectrum' (b)' Band'spectrum' (c)' Continuous'spectrum' (d)' None'of'these' ' '18.'The'process'of'heat'transfer'in'which'heat'is'transferred'with'actual'migration'of' medium'particles'is'known'as'(AFMCU94)' (a)' Conduction' (b)' Convection' (c)' Radiation' (d)' Reflection' ' 19.'Dimensions'of'surface'tension'are:' (a)' [M2L2T2]' (b)' [M2LT2]' (c)' [MT2]' (d)' [MLT2]' ' 20.'In'an'atom'bomb'the'reaction'which'occurs'is:' (a)' Thermo'nuclear' (b)' Uncontrolled'fission' (c)' )'Controlled'fission' (d)' Fusion' ' 21.'Which'instrument'is'used'to'measure'altitudes'in'aircraft's?' (a)' Audiometer' (b)' Ammeter' (c)' Altimeter' (d)' Anemometer' ' ' ' ' 22.'Which'instrument'is'used'to'measure'depth'of'ocean?' (a)' Galvanometer' (b)' Fluxmeter' (c)' Endoscope' (d)' Fathometer' ' 23.'Name'of'the'instrument'to'measure'atmospheric'pressure'?' (a)' Barometer' (b)' Barograph' (c)' Bolometer' (d)' Calipers' ' 24.'Which'instrument'is'used'to'determine'the'intensity'of'colors?' (a)' Cathetometer' (b)' Chronometer' (c)' Colorimeter' (d)' Commutator'


'


' 25.'Thomas'Alva'Edison'invented' (a)' Cinema' (b)' Cine'Camera' (c)' Computer' (d)' Cinematograph' ' 26.'Alfred'Nobel'invented' (a)' X'ray' (b)' Diesel'Engine' (c)' Dynamite' (d)' Dynamo' ' 27.'David'Hughes'invented' (a)' Machine'Gun' (b)' Microphone' (c)' Microscope' (d)' Motorcycle' ' 28.'Who'discovered'Atom?' (a)' Madam'Curie' (b)' James'Chadwick' (c)' Rutherford' (d)' John'Dalton' ' 29.'The'absorption'of'ink'by'blotting'paper'involves' (a)' capillary'action'phenomenon' (b)' viscosity'of'ink' (c)' siphon'action' (d)' diffusion'of'ink'through'the'blotting' ' 30.'Unit'of'Pressure'is' (a)' newton'second' (b)' Pascal' (c)' watt' (d)' newton'per'meter' ' 31.'Radian'per'second'is'unit'of' (a)' Momentum' (b)' Moment'of'Inertia' (c)' Frequency' (d)' Angle'Velocity' ' 32.'What'is'unit'of'Work'and'Energy?' (a)' Joule' (b)' kilogram' (c)' ampere' (d)' meter' ' 33.'What'is'unit'of'Viscosity?' (a)' coulomb' (b)' newton'second'per'square'meter' (c)' watt'per'meter'per'degree'Celsius' (d)' joule'per'kilogram'per'Kelvin' ' 34.'What'is'unit'of'Electrical'Capacity'?' (a)' henry' (b)' farad' (c)' volt' (d)' ohm'


' 35.'Scalar'Quantities'are' (a)' physical'quantities'which'have' magnitude'only'and'no'direction' (c)' physical'quantities'which'have' magnitude'only'and'direction' ' 36.'What'is'displacement'?' (a)' Longest'distance'covered'by'a' body'in'a'random'direction' (c)' Shortest'distance'covered'by'a' body'in'a'definite'direction' ' 37.'Which'law'is'also'called'law'of'inertia'?' (a)' Newton'first'law' (c)' Newton'third'law' ' 38.'What'is'newton'third'law'of'motion'?' (a)' Everybody'maintains'its'initial' state'rest'or'motion'unless'no' external'force'is'applied'

'


(b)' physical'quantities'which'have'no' magnitude'only'and'only'direction' (d)' physical'quantities'which'have'no' magnitude'and'no'direction' (b)' Shortest'distance'covered'by'a'body' in'a'random'direction' (d)' Longest'distance'covered'by'a'body' in'a'definite'direction' (b)' Newton'second'law' (d)' All'of'above'

(b)' The'rate'of'change'in'momentum'of' a'body'is'directly'proportional'to'the' applied'force'on'the'body'and'takes' place'in'the'direction'of'force.' (c)' To'every'action'there'is'equal'and' (d)' None'of'above' opposite'reaction'

' 39.'Energy'posses'by'a'body'in'motion'is'called' (a)' Kinetic'Energy' (b)' Potential'Energy' (c)' Both'of'Above' (d)' None'of'Above' ' 40.'Electric'Motor'converts' (a)' Electrical'energy'into'mechanical' (b)' Mechanical'energy'into'Electrical' energy' energy' (c)' Electrical'energy'into'light'energy' (d)' None'of'above' ' 41.'Atmospheric'pressure'is'measured'by' (a)' Tonometer' (b)' Pyrometer' (c)' Barometer' (d)' Thermometer' ' 42.'Force'of'attraction'between'the'molecules'of'different'substances'is'called' (a)' Surface'tension' (b)' Cohesive'force'


(c)' Adhesive'force'

'


(d)' None'of'above'

' 43.'Longitudinal'waves'and'Transverse'waves'are'types'of'?' (a)' Mechanical'waves' (b)' NonUMechanical'waves' (c)' Both'of'above' (d)' None'of'Above' ' 44.'Which'of'the'following'is'an'electromagnetic'wave'?' (a)' Cathode'rays' (b)' Sound'wave' (c)' Ultrasonic'wave' (d)' Infra'red'rays' ' 45.'What'is'the'relation'between'wavelength,'frequency'and'velocity'?' (a)' velocity'of'wave'='frequency'*' (b)' velocity'of'wave'=' wavelength' frequency/wavelength' (c)' velocity'of'wave'=' (d)' None'of'above' wavelength/frequency' ' 46.'What'are'audible'sound'waves'?' (a)' Having'frequency'less'than'20'Hz' (b)' Having'frequency'between'20'Hz'to' 20000'Hz' (c)' Having'frequency'more'than' (d)' None'of'above' 20000'Hz' ' 47.'What'is'refractive'index'?' (a)' it'is'defined'as'the'ratio'of'speed' (b)' it'is'defined'as'the'ratio'of'speed'of' of'light'in'the'medium'to'the' light'in'vacuum'to'the'speed'of'light' speed'of'light'in'vacuum' in'the'medium' (c)' it'is'defined'as'the'product'of' (d)' None'of'above' speed'of'light'in'medium'and'in' ' vacuum' ' 48.'Which'are'the'primary'Colours?' (a)' Yellow,'Green,'Blue' (b)' Red,'Magenta,'Blue' (c)' Red,'Green,'White' (d)' Red,'Green,'Blue' ' 49.'Device'used'to'measure'potential'difference'between'two'points'in'a'circuit'is'?' (a)' Ammeter' (b)' Galvanometer' (c)' Voltmeter' (d)' None'of'above' ' ! ! !


1.!!(a)!

2.!(a)!

'


Answers:'Engineering'Physics'MCQs' ! 3.!(b)! 4.!(b)! 5.!(a)! 6.!(a)! 7.!(d)! 8.!(a)!

9.!(c)!

10.!(b)!

11.!(d)! 12.!(a)! 13.!(c)! 14.!(b)! 15.!(c)! 16.!(b)! 17.!(c)! 18.!(b)! 19.!(c)! 20.!(b)! 21.!(c)! 22.!(d)! 23.!(a)! 24.!(c)! 25.!(d)! 26.!(c)! 27.!(b)! 28.!(d)! 29.!(a)! 30.!(b)! 31.!(d)! 32.!(a)! 33.!(b)! 34.!(b)! 35.!(a)! 36.!(c)! 37.!(a)! 38.!(c)! 39.!(a)! 40.!(a)! 41.!(c)! 42.!(c)! 43.!(a)! 44.!(d)! 45.!(a)! 46.!(b)! 47.!(b)! 48.!(d)! 49.!(c)! ! '

Engineering Drawing

Contents 1 Projection of straight line

1

2 Projections of Planes

2

3 Projections of Solids

3

4 Intersection of surfaces

4

5 Isometric Projections

5

6 Sectional view of solids

6

7 Computer Aided Drafting (CAD)

7

1

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Projection of straight line

Straight line is the Locus of a point, which moves linearly. Straight line is also the shortest distance between any two given points. The projection of a line can be obtained by projecting its end points on planes of projections and then connecting the points of projections. The projected length and inclination of a line, can be different compared to its true length and inclination. When a line is parallel to one plane and inclined to the other, The projection of the line on the plane to which it is parallel will show its true length. The projected length on the plane to which it is inclined will always be shorter than the true length. In figure 2, the line AB is parallel to VP and is inclined to HP. The angle of inclination of AB with HP is being Îÿ degrees. Projection of line AB on VP is aâ èbâ è and is the true length of AB. The projection of line AB on HP is indicated as line ab. Length ab is shorter than the true length AB of the line.

1

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2

Projections of Planes

A plane is as two dimensional surface having length and breadth with negligible thickness. They are formed when any three or more non-collinear points are joined. Planes are bounded by straight/curved lines and may be either regular or an irregular. Regular plane surfaces are in which all the sides are equal. Irregular plane surfaces are in which the lengths of the sides are unequal. Casting projection of a plane is more complex even though the procedure is same as that of a straight line. For a plane inclined at „ to VP(vertical plane) and perpendicular to HP(horizontal plane) Draw the projections of a triangular lamina (plane surface) placed in the first quadrant with its surface is inclined at f to VP and perpendicular to the HP. Since the lamina is inclined to VP, it is also inclined to left PP at (90 ≠ „). The triangular lamina ABC is projected onto VP, HP and left PP. a’b’c’ - is the front view projected on VP. a”b”c” - is the right view projected on left PP. Since lamina is inclined to VP and PP, front and side views are not in true shape. Since lamina is perpendicular to HP, its top view is projected as a line acb.

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Engineering Drawing

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Projections of Solids

Solids are three dimensional objects that have considerable amount of length, width and height. Unlike lines or planes, for a solid every vertex has three adjacent vertices. To project a solid on the three planes, they are placed first in the simple position and then tilted successively in two or three stages to obtain the final position. Following is an example. Method of obtaining the top and the front views of the pyramid when it lies on HP on one of its base edges with its axis or the base inclined to HP. If the solid is required to be placed with an edge of the base on HP, then initially the solid has to be placed with its base on HP such that an edge of the base is perpendicular to VP, i.e., to XY line in top view preferably to lie on the right side. When a pentagonal prism has to be placed with an edge of base on HP such that the base or axis is inclined to HP, then initially, the prism is placed with its base on HP with an edge of the base perpendicular to VP and the lying on the right side. In this position, the first set of top and front views are drawn with the base edges (c1 )(d1 ) perpendicular to XY line in the top view. In the front view, this edge cÕ1 (dÕ1 ) appears as a point. Since the prism has to lie with an edge of the base on HP, the front view of the prism is tilted on the edge cÕ1 (dÕ1 ) such that the axis is inclined at q to HP. Redraw the first front view in the tilted position. Whenever the inclination of axis q with HP is given, first the base is drawn at (90 ≠ ◊) in the front view, otherwise improper selection of the position of the axis may result in the base edge cÕ1 (dÕ1 ) lying above or below the XY line. The second top view is projected by drawing the vertical projectors from the corners of the second front view and the horizontal projectors from the first top view. The figure below shows the sequence in obtaining the projection of the solid for the above case.


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4

Intersection of surfaces

Whenever two or more solids combine, a definite curve is seen at their intersection. This curve is called the curve of intersection (COI). Lines of intersection are a common feature in engineering applications or products. To understand their projection process let’s look at the following example. Consider a vertical cylinder of 80 mm diameter is completely penetrated by another cylinder of 60 mm diameter, their axes bisecting each other at right angles. Assume the axis of the penetrating cylinder to be parallel to the VP. Following is procedure to obtain their projection. The Front view, top view and side view of the two cylinders are drawn without the intersection lines. Divide the circumference of the circle in the side view in to 12 equal parts. Draw horizontal projectors from these points on to the front view. Project the same points from the side view on to the top view and obtain lines 1-1, 2-2, 3-3, etc. Let us now consider a horizontal section plane passing through points 2-2 and 12-12. In the front view, it will be seen as a line coinciding with line 2â è 2’. In the top view, the section of the horizontal cylinder will be a rectangle of width (i.e. the line 2-12). The section of the vertical cylinder will be a circle. Points p2 and p12 at which the sides (2-2 and 12-12) of the rectangle cuts the circle will lie on the curve of intersection. This point is first obtained in the top view by the intersecting point of line 12-12 and 2-2 with the circle. Vertical projector lines are drawn from these points to the front view so as to intersect Õ with the horizontal projectors drawn through points 2 and 12 in the side view to obtain P2Õ and P12 in the front view. Other cutting planes are also assumed passing through 3-11, 4-10, etc. and the procedure repeated to obtain other points pÕ3 , pÕ4 , pÕ5 , etc. Similar procedure is adopted to obtain points q1Õ , q2Õ , etc. on the right hand side. Since the axis to the two cylinders intersect, points pÕ2 and pÕ12 will coincide and hence cannot be shown in the figure.

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Engineering Drawing

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5

Isometric Projections

Isometric projection is a method for visually representing three-dimensional objects in two dimensions. The four basic steps for creating an isometric drawing are: • Positioning the object. Determine the isometric viewpoint that clearly depicts maximum features of the object. • Once the object is positioned and the view point is decided, draw the isometric axes which will produce that view-point.

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• Construct isometric planes, using the overall width (W), height (H), and depth (D) of the object, such that the object will be totally enclosed in a box. • Locate details on the isometric planes. Darken all visible lines, and eliminate hidden lines unless absolutely necessary to describe the object. The step wise procedure for drawing isometric view of an object having isometric planes only are shown in figure. 1. Step 1: Determine the desired view of the object. Here the object will be viewed from above (regular isometric). The isometric axes are then drawn as shown in step-1. 2. Step 2: Construct the front isometric plane using W and H dimensions. Width dimensions are drawn along 30o lines from the horizontal. Height dimensions are drawn as vertical lines. The step wise procedure for drawing isometric view of an object having isometric planes only are shown in figure. 3. Step 3: Construct the top isometric plane using the W and D dimensions. Both W and D dimensions are drawn along 30o lines from the horizontal. 4. Step 4: Construct the right side isometric plane using D and H dimensions. Depth dimensions are drawn along 30o lines and height dimensions are drawn as vertical lines. 5. Step 5: Transfer some distances for the various features from the multi-view drawing to the isometric lines that make up the isometric rectangle on the front and top planes of the isometric box, e.g. distance A is measured from the multi-view drawing. It is then transferred along the width line in the front plane of the isometric rectangle. Draw the details of the block by drawing isometric lines between the points transferred from the multi-view drawing, e.g., the notch is taken out of the block by locating its position on the front and the top planes of the isometric box.


Engineering Drawing

Page: 6 6. Step 6: Transfer the remaining features from the multi-view drawing to the isometric drawing. Block in the details by connecting endpoints of the measurements taken from the multi-view drawing. 7. Step 7: Darken all visible lines and erase or lighten the construction lines to complete the isometric drawing of the object

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Sectional view of solids

Sectional drawings are multi-view technical drawings that contain special views of a part or parts, that reveal interior features. A primary reason for creating a section view is the elimination of hidden lines, so that a drawing can be more easily understood or visualized. Traditional section views are based on the use of an imaginary cutting plane that cuts through the object to reveal interior features. This imaginary cutting plane is controlled by the designer and is generally represented by any of the following: • Full section view, where the section plane goes completely through the object. • Half section view, where the section plane goes half-way through the object.

• Offset section, where the sectional plane bent through the features that are not aligned. • Broken-out section where the section goes through part of the object.


Engineering Drawing

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7

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Computer Aided Drafting (CAD)

Computer-aided drafting (CAD) is the use of computer systems to assist in the creation, modification, analysis, or optimization of a design. CAD output is often in the form of electronic files for print, machining, or other manufacturing operations. CAD software for mechanical design uses either vector-based graphics to depict the objects of traditional drafting, or may also produce raster graphics showing the overall appearance of designed objects. However, it involves more than just shapes. As in the manual drafting of technical and engineering drawings, the output of CAD must convey information, such as materials, processes, dimensions, and tolerances, according to application-specific conventions. CAD may be used to design curves and figures in two-dimensional (2D) space; or curves, surfaces, and solids in three-dimensional (3D) space.


Engineering Drawing

Analog and Digital Electronics

Contents 1 Characteristics of diodes 1.1 Bipolar Junction Transistors (BJT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Junction Field Effect Transistors (JFET) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Metal-oxide Semiconductor Field-effect Transistor (MOSFET) . . . . . . . . . . . . . . . . . . 2 Amplifiers 2.1 Biasing . . . . . . 2.2 Equivalent circuit . 2.3 Frequency response 2.4 Oscillators . . . . . 2.5 Feedback amplifiers

2 2 5 8

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10 10 13 14 15 15

3 Operational Amplifier 3.1 Characteristics of op-amp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16 16

4 Active Filters

17

5 Voltage Controlled Oscillator

17

6 Multiplexer

19

7 Schmitt Trigger

19

8 Multi-vibrators

20

9 Sample and Hold Circuits

20

10 Analog to Digital Convertors

21

11 Digital to Analog Convertors

21

12 8-bit Microprocessors 12.1 Architecture of 8051 microprocessor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1

Characteristics of diodes

1.1

Bipolar Junction Transistors (BJT)

The three parts of a BJT are collector, emitter and base. Before knowing about the bipolar junction transistor characteristics, we have to know about the modes of operation for this type of transistors. The modes are: • Common Base (CB) mode

• Common Emitter (CE) mode

• Common Collector (CC) mode All three types of modes are shown below

Now coming to the characteristics of BJT there are different characteristics for different modes of operation. Characteristics is nothing but the graphical forms of relationships among different current and voltage variables of the transistor. The characteristics for p - n - p transistors are given for different modes and different parameters.

Common Base Characteristics Input Characteristics For p - n - p transistor, the input current is the emitter current (IE ) and the input voltage is the collector base voltage (VCB ).

As the emitter - base junction is forward biased, therefore the graph of IE V s VEB is similar to the forward characteristics of a p - n diode. IE increases for fixed VEB when VCB increases. Output Characteristics The output characteristics shows the relation between output voltage and output current IC is the output current and collector - base voltage and the emitter current IE is the input current and works as the parameters. The figure below shows the output characteristics for a p - n - p transistor in CB mode.



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As we know for p - n - p transistors IE and VEB are positive and IC , IB , VCB are negative. These are three regions in the curve, active region saturation region and the cut off region. The active region is the region where the transistor operates normally. Here the emitter junction is reverse biased. Now the saturation region is the region where both the emitter collector junctions are forward biased. And finally the cut off region is the region where both emitter and the collector junctions are reverse biased.

Common Emitter Characteristics Input Characteristics IB (Base Current) is the input current, VBE (Base - Emitter Voltage) is the input voltage for CE (Common Emitter) mode. So, the input characteristics for CE mode will be the relation between IB and VBE with VCE as parameter. The characteristics are shown below

The typical CE input characteristics are similar to that of a forward biased of p - n diode. But as VCB increases the base width decreases. Output Characteristics Output characteristics for CE mode is the curve or graph between collector current (IC) and collector emitter voltage (VCE ) when the base current IB is the parameter. The characteristics is shown below in the figure.



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Like the output characteristics of common - base transistor CE mode has also three regions named (i) Active region, (ii) cut-off regions, (iii) saturation region. The active region has collector region reverse biased and the emitter junction forward biased. For cut-off region the emitter junction is slightly reverse biased and the collector current is not totally cut-off. And finally for saturation region both the collector and the emitter junction are forward biased.

Common Collector Characteristics IC , varies with the collector-to-emitter voltage, VCE , for specified values of base current, IB . Notice in the circuit diagram that both VBB and VCC are variable sources of voltage. Assume that VBB is set to produce a certain value of IB and VCC is zero. For this condition, both the base-emitter junction and the base-collector junction are forward-biased because the base is at approximately 0.7 V while the emitter and the collector are at 0 V. The base current is through the base-emitter junction because of the low impedance path to ground and, therefore, IC is zero. When both junctions are forwardbiased, the transistor is in the saturation region of its operation. Saturation is the state of a BJT in which the collector current has reached a maximum and is independent of the base current. As VCC is increased, VCE increases as the collector current increases. This is indicated by the portion of the characteristic curve between points A and B in Figure.

IC increases as VCC is increased because VCE remains less than 0.7 V due to the forward-biased basecollector junction. Ideally, when VCE exceeds 0.7 V, the base-collector junction becomes reverse-biased and the transistor goes into the active, or linear, region of its operation. Once the base collector junction is reverse-biased, IC



Page: 5 levels off and remains essentially constant for a given value of IB as VC E continues to increase. Actually, IC increases very slightly as VCE increases due to widening of the base-collector depletion region. This results in fewer holes for recombination in the base region which effectively causes a slight increase in —DC . This is shown by the portion of the characteristic curve between points B and C in figure. For this portion of the characteristic curve, the value of IC is determined only by the relationship expressed as IC = —DC IB . When VCE reaches a sufficiently high voltage, the reverse-biased base-collector junction goes into breakdown; and the collector current increases rapidly as indicated by the part of the curve to the right of point C in figure above. A transistor should never be operated in this breakdown region. A family of collector characteristic curves is produced when IC versus VC E is plotted for several values of IB , as illustrated in figure below. When IB = 0, the transistor is in the cut-off region although there is a very small collector leakage current as indicated. Cut-off is the non-conducting state of a transistor. The amount of collector leakage current for IB = 0 is exaggerated on the graph for illustration.

1.2

Junction Field Effect Transistors (JFET)

There are two types of characteristics: 1. Output or drain characteristic 2. Transfer characteristic

Output or Drain Characteristic The curve drawn between drain current Ip and drain-source voltage VDS with gate-to source voltage VGS as the parameter is called the drain or output characteristic. This characteristic is analogous to collector characteristic of a BJT: Drain Characteristic With Shorted-Gate The circuit diagram for determining the drain characteristic with shorted-gate for an N-channel JFET is given in figure. and the drain characteristic with shorted-gate is shown in another figure.



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Initially when drain-source voltage Vns is zero, there is no attracting potential at the drain, so no current flows inspite of the fact that the channel is fully open. This gives drain current Ip = 0. For small applied voltage Vna , the N-type bar acts as a simple semiconductor resistor, and the drain current increases linearly with the increase in Vds , upto the knee point. This region, (to the left of the knee point) of the curve is called the channel ohmic region, because in this region the FET behaves like an ordinary resistor. With the increase in drain current ID , the ohmic voltage drop between the source and channel region reverse-biases the gate junction. The reverse-biasing of the gate junction is not uniform throughout., The reverse bias is more at the drain end than that at the source end of the channel, so with the increase in Vds , the conducting portion of the channel begins to constrict more at the drain end. Eventually a voltage Vds is reached at which the channel is pinched off. The drain current ID no longer increases with the increase in Vds . It approaches a constant saturation value. The value of voltage VDS at which the channel is pinched off (i.e. all the free charges from the channel get removed), is called the pinch-off voltage Vp . The pinch-off voltage Vp , not too sharply defined on the curve, where the drain current ID begins to level off and attains a constant value. From point A (knee point) to the point B (pinch-off point) the drain current ID increases with the increase In voltage Vds following a reverse square law. The region of the characteristic in which drain current ID remains fairly constant is called the pinch-off region. It is also sometimes called the saturation region or amplifier region. In this region the JFET operates as a constant current device since drain current (or output current) remains almost constant. It is the normal operating region of the JFET when used as an amplifier. The drain current in the pinch-off region with VGS = 0 is referred to the drain-source saturation current, Idss). It is to be noted that in the pinch-off (or saturation) region the channel resistance increases in proportion to increase in VDS and so keeps the drain current almost constant and the reverse bias required by the gate-channel junction is supplied entirely by the voltage drop across the channel resistance due to flow of IDsg and not by the external bias because VGS = 0. Drain current in the pinch-of region is given by Shockleyâ ès equation, where ID is the drain current at a given gate-source voltage VGS , IDSS is the drain-current with gate shorted to source and VGS (0FF) is the gate-source cut-off voltage. If drain-source voltage, Vds is continuously increased, a stage comes when the gate-channel junction breaksdown. At this point current increases very rapidly. and the JFET may be destroyed. This happens because the charge carriers making up the saturation current at the gate channel junction accelerate to a high velocity and produce an avalanche effect. Drain Characteristics With External Bias The circuit diagram for determining the drain characteristics with different values of external bias is shown in figure. and a family of drain characteristics for different values of gate-source voltage VGS is given in next figure



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It is observed that as the negative gate bias voltage is increased • The maximum saturation drain current becomes smaller because the conducting channel now becomes narrower. • Pinch-off voltage is reached at a lower value of drain current ID than when VGS = 0. When an external bias of, say - 1 V is applied between the gate and the source, the gate-channel junctions are reversebiased even when drain current, ID is zero. Hence the depletion regions are already penetrating the channel to a certain extent when drain source voltage, VDS is zero. Due to this reason, a smaller voltage drop along the channel (i.e. smaller than that for VGS = 0) will increase the depletion regions to the point where 1 they pinch-off the current. Consequently, the pinch-off voltage VP is reached at a lower 1 drain current, ID when VGS = 0. • The ohmic region portion decreases.

• Value of drain-source voltage VDS for the avalanche breakdown of the gate junction is reduced. For working of JFET in the pinch-off or active region it is necessary that the following conditions be fulfilled. • Vp < VDS < VDS (max) • VGS (of f ) < VGS < 0 • 0 < ID < IDSS

Transfer Characteristic of JFET



Page: 8 The transfer characteristic for a JFET can be determined experimentally, keeping drain-source voltage, VDS constant and determining drain current, ID for various values of gate-source voltage, VGS . The circuit diagram is shown in fig. 9.7 (a). The curve is plotted between gate-source voltage, VGS and drain current, ID . It is similar to the transconductance characteristic of a vacuum tube or a transistor. It is observed that • Drain current decreases with the increase in negative gate-source bias • Drain current, ID = IDSS when VGS = 0 • Drain current, ID = 0 when VGS = VD

The transfer characteristic can also be derived from the drain characteristic by noting values of drain current, ID corresponding to various values of gate-source voltage, VGS for a constant drain-source voltage and plotting them.

1.3

Metal-oxide Semiconductor Field-effect Transistor (MOSFET)

Steady state output i-v characteristics of a MOSFET The MOSFET, like the BJT is a three terminal device where the voltage on the gate terminal controls the flow of current between the output terminals, Source and Drain. The source terminal is common between the input and the output of a MOSFET. The output characteristics of a MOSFET is then a plot of drain current (iD ) as a function of the Drain Source voltage (vDS ) with gate source voltage (vGS ) as a parameter.

With gate-source voltage (VGS ) below the threshold voltage (vGS (th)) the MOSFET operates in the cutoff mode. No drain current flows in this mode and the applied drain-source voltage (vDS ) is supported by the body-collector p-n junction. Therefore, the maximum applied voltage should be below the avalanche break down voltage of this junction (VDSS ) to avoid destruction of the device. When VGS is increased beyond vGS (th) drain current starts flowing. For small values of vDS (vDS < (vGS ≠ vGS (th))iD is almost proportional to vDS . Consequently this mode of operation is called ”ohmic mode” of operation. In power electronic applications a MOSFET is operated either in the cut off or in the ohmic mode. The slope of the vDS ≠ iD characteristics in this mode is called the ON state resistance of the MOSFET (rDS (ON )).



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Several physical resistances as shown in figure above contribute to rDS (ON ). Note: rDS (ON ) reduces with increase in vGS . This is mainly due to reduction of the channel resistance at higher value of vGs . Hence, it is desirable in power electronic applications, to use a large gate-source voltage as possible subject to the dielectric break down limit of the gate-oxide layer. At still higher value of vDS (vDS > (vGS ≠ vGS (th)) the iD ≠ vDS characteristics deviates from the linear relationship of the ohmic region and for a given vGS , iD tends to saturate with increase in vDS . The exact mechanism behind this is rather complex. It will suffice to state that, at higher drain current the voltage drop across the channel resistance tends to decrease the channel width at the drain drift layer end. In addition, at large value of the electric field, produced by the large Drain - Source voltage, the drift velocity of free electrons in the channel tends to saturate as shown below.

The drain current becomes independent of VDS and determined solely by the gate - source voltage vGS . This is the active mode of operation of a MOSFET. Switching characteristics of a MOSFET Like any other power semiconductor device a MOSFET is used as a switch in all power electronic converters. As a switch a MOSFET operates either in the cut off mode (switch off) or in the ohmic mode (switch on). While making transition between these two states it traverses through the active region. Being a majority carrier device the switching process in a MOSFET does not involve any inherent delay due to redistribution of minority charge carriers. However, formation of the conducting channel in a MOSFET and its disappearance require charging and discharging of the gate-source capacitance which contributes to the switching times. There are several other capacitors in a MOSFET structure which are also involved in the switching process.



Page: 10 Unlike bipolar devices, however, these switching times can be controlled completely by the gate drive circuit design.

Figure above shows three important capacitances inherent in a MOSFET structure. The most prominent capacitor in a MOSFET structure is formed by the gate oxide layer between the gate metallization and the n+ type source region. It has the largest value (a few nano farads) and remains more or less constant for all values of vGS and vDS . The next largest capacitor (a few hundred pico forwards) is formed by the drain â body depletion region directly below the gate metallization in the n- drain drift region. Being a depletion layer capacitance its value is a strong function of the drain source voltage vDS . For low values of vDS (vDS < (vGS ≠ vGS (th))) the value of CGD (CGD2) is considerably higher than its value for large vDS .

2

Amplifiers

2.1

Biasing

Transistor Biasing is the process of setting a transistors DC operating voltage or current conditions to the correct level so that any AC input signal can be amplified correctly by the transistor. A transistors steady state of operation depends a great deal on its base current, collector voltage, and collector current and therefore, if a transistor is to operate as a linear amplifier, it must be properly biased to have a suitable operating point.

Base biasing a common emitter amplifier One of the most frequently used biasing circuits for a transistor circuit is with the self-bias of the emitter-bias circuit where one or more biasing resistors are used to set up the initial DC values of transistor currents, (IB ), (IC ) and (IE ). The two most common forms of transistor biasing are: Beta Dependent and Beta Independent. Transistor bias voltages are largely dependent on transistor beta, (—) so the biasing set up for one transistor may not necessarily be the same for another transistor. Transistor biasing can be achieved either by using a single feed back resistor or by using a simple voltage divider network to provide the required biasing voltage. 1. Current Biasing a Transistor: The circuit shown is called as a ”fixed current bias circuit”, because the transistors base current, IB remains constant for given values of Vcc , and therefore the transistors operating point must also remain fixed. This two resistor biasing network is used to establish the initial operating region of the transistor using a fixed current bias.



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This type of transistor biasing arrangement is also beta dependent biasing as the steady-state condition of operation is a function of the transistors beta Îö value, so the biasing point will vary over a wide range for transistors of the same type as the characteristics of the transistors will not be exactly the same. The emitter diode of the transistor is forward biased by applying the required positive base bias voltage via the current limiting resistor RB . Assuming a standard bipolar transistor, the forward base-emitter voltage drop will be 0.7V. Then the value of RB is simply: (VCC ≠ VBE )/IB where IB is defined as IC /— 2. Feedback biasing a transistor This self-biasing configuration is another beta dependent biasing method that requires only two resistors to bias the transistor. The collector to base feedback configuration ensures that the transistor is always biased in the active region regardless of the value of Beta (—) as the base bias is derived from the collector voltage.

In this circuit, the base bias resistor, RB is connected to the transistors collector C, instead of to the supply voltage rail, Vcc . Now if the collector current increases, the collector voltage drops, reducing the base drive and thereby automatically reducing the collector current. Then this method of biasing produces negative feedback. The biasing voltage is derived from the voltage drop across the load resistor, RL . So if the load current increases there will be a larger voltage drop across RL , and a corresponding reduced collector voltage, VC which will cause a corresponding drop in the base current, IB which in turn, brings IC back to normal. The opposite reaction will also occur when transistors collector current becomes less. Then this method of biasing is called self-biasing with the transistors stability using this type of feedback bias network being generally good for most amplifier designs. Engineering Knowledge Test


Page: 12 3. Dual feedback transistor biasing Adding an additional resistor to the base bias network of the previous configuration improves stability even more with respect to variations in Beta, (—) by increasing the current flowing through the base bias resistors.

The current flowing through RB1 is generally set at a value equal to about 10 percent of collector current, IC . Obviously it must also be greater than the base current required for the minimum value of Beta, —. One of the advantages of this type of self-biasing configuration is that the resistors provide both automatic biasing and Rf feedback at the same time. 4. Transistor biasing with emitter feedback This type of transistor biasing configuration, often called self-emitter biasing, uses both emitter and collector-base feedback to stabilize the collector current but the output has reduced gain because of the base resistor connection.

The current flowing from the emitter causes a voltage drop across RE in such a direction, that it forward biases the emitter-base junction. So if the emitter current increases, voltage drop IRE also increases. Since the polarity of this voltage reverse biases the emitter-base junction, IB automatically decrease. Therefore the emitter current increase less than it would have done had there been no self-biasing resistor. Resistor values are generally set so that the voltage drop across emitter resistor RE is approximately 10 percent of VCC and the current flowing through resistor RB1 is 10 percent of the collector current IC . 5. Voltage divider transistor biasing



Page: 13 The common emitter transistor is biased using a voltage divider network. The name of this biasing configuration comes from the fact that the two resistors RB1 and RB2 are connected to the transistors base terminal across the supply.

This voltage divider configuration is the most widely used transistor biasing method, as the emitter diode of the transistor is forward biased by the voltage dropped across resistor RB2 . Also, voltage divider network biasing makes the transistor circuit independent of changes in beta as the voltages at the transistors base, emitter, and collector are dependent on external circuit values. To calculate the voltage developed across resistor RB2 and therefore the voltage applied to the base terminal we simply use the voltage divider formula for resistors in series. The current flowing through resistor RB2 is generally set at 10 times the value of the required base current IB so that it has no effect on the voltage divider current or changes in Beta. The goal of Transistor Biasing is to establish a known Q-point in order for the transistor to work efficiently and produce an undistorted output signal. Correct biasing of the transistor also establishes its initial AC operating region with practical biasing circuits using either a two or four-resistor bias network.

2.2

Equivalent circuit

Amplifiers are used extensively in electronic circuits to make an electronic signal bigger without affecting it in any other way. Generally we think of Amplifiers as audio amplifiers in the radios, CD players and stereoâ ès we use around the home. In this amplifier tutorial section we looked at the amplifier which is based on a single bipolar transistor as shown below, but there are several different kinds of transistor amplifier circuits that we could use.

Single Stage Amplifier Circuit • Small Signal Amplifiers are also known as Voltage Amplifiers. Engineering Knowledge Test


Page: 14 • Voltage Amplifiers have 3 main properties, Input Resistance, Output Resistance and Gain.

• The Gain of a small signal amplifier is the amount by which the amplifier ”Amplifies” the input signal.

• Gain is a ratio of input divided by output, therefore it has no units but is given the symbol (A) with the most common types of transistor gain being, Voltage Gain (Av), Current Gain (Ai) and Power Gain (Ap) • The power Gain of the amplifier can also be expressed in Decibels or simply dB.

• In order to amplify all of the input signal distortion free in a Class A type amplifier, DC Base Biasing is required. • DC Bias sets the Q-point of the amplifier half way along the load line.

• This DC Base biasing means that the amplifier consumes power even if there is no input signal present. • The transistor amplifier is non-linear and an incorrect bias setting will produce large amounts of distortion to the output waveform.

• Too large an input signal will produce large amounts of distortion due to clipping, which is also a form of amplitude distortion. • Incorrect positioning of the Q-point on the load line will produce either Saturation Clipping or Cut-off Clipping. • The Common Emitter Amplifier configuration is the most common form of all the general purpose voltage amplifier circuit using a Bipolar Junction Transistor. • The Common Source Amplifier configuration is the most common form of all the general purpose voltage amplifier circuit using a Junction Field Effect Transistor.

2.3

Frequency response

Amplifiers and filters are widely used electronic circuits that have the properties of amplification and filtration, hence their names. Amplifiers produce gain while filters alter the amplitude and/or phase characteristics of an electrical signal with respect to its frequency. As these amplifiers and filters use resistors, inductors, or capacitor networks (RLC) within their design, there is an important relationship between the use of these reactive components and the circuits frequency response characteristics. Frequency Response of an electric or electronics circuit allows us to see exactly how the output gain (known as the magnitude response) and the phase (known as the phase response) changes at a particular single frequency, or over a whole range of different frequencies from 0Hz, (d.c.) to many thousands of mega-hertz, (MHz) depending upon the design characteristics of the circuit. Graphical representations of frequency response curves are called Bode Plots and as such Bode plots are generally said to be a semi-logarithmic graphs because one scale (x-axis) is logarithmic and the other (y-axis) is linear (log-lin plot) as shown.



Page: 15 Then we can see that the frequency response of any given circuit is the variation in its behaviour with changes in the input signal frequency as it shows the band of frequencies over which the output (and the gain) remains fairly constant. The range of frequencies either big or small between fL and fH is called the circuits bandwidth. So from this we are able to determine at a glance the voltage gain (in dB) for any sinusoidal input within a given frequency range. As mentioned above, the Bode diagram is a logarithmic presentation of the frequency response. Most modern audio amplifiers have a flat frequency response as shown above over the whole audio range of frequencies from 20 Hz to 20 kHz. This range of frequencies, for an audio amplifier is called its Bandwidth, (BW) and is primarily determined by the frequency response of the circuit. Frequency points fL and fH relate to the lower corner or cut-off frequency and the upper corner or cut-off frequency points respectively were the circuits gain falls off at high and low frequencies. These points on a frequency response curve are known commonly as the -3dB (decibel) points. So the bandwidth is simply given as: Bandwitdth, (BW ) = fH ≠ fL

The decibel, (dB) which is 1/10th of a bel (B), is a common non-linear unit for measuring gain and is defined as 20log10 (A) where A is the decimal gain, being plotted on the y-axis. Zero decibels, (0dB) corresponds to a magnitude function of unity giving the maximum output. In other words, 0dB occurs when Vout = Vin as there is no attenuation at this frequency level and is given as: Vout = 1, Vin

20log(1) = 0

We see from the Bode plot above that at the two corner or cut-off frequency points, the output drops from 0dB to -3dB and continues to fall at a fixed rate. This fall or reduction in gain is known commonly as the roll-off region of the frequency response curve. In all basic single order amplifier and filter circuits this roll-off rate is defined as 20dB/decade, which is an equivalent to a rate of 6dB/octave. These values are multiplied by the order of the circuit. These -3dB corner frequency points define the frequency at which the output gain is reduced to 70.71 percent of its maximum value. Then we can correctly say that the -3dB point is also the frequency at which the systems gain has reduced to 0.707 of its maximum value. Frequency Response -3dB Point: ≠3dB = 20log10 (0.7071) The -3dB point is also known as the half-power points since the output power at this corner frequencies will be half that of its maximum 0dB value.

2.4

Oscillators

Oscillators are the circuits that produce an alternating output without any alternating input. They produce a periodic, oscillating electronic signal, often a sine wave or a square wave (pulses). These circuits convert direct current from a power supply into alternating current signal. Oscillators are classified based on the frequency ranges of their output signals. There are three categories given below. • Audio Oscillator (16 Hz to 20 KHz)

• Radio Oscillator (100 KHz to 100 GHz)

• Low Frequency Oscillator (below 20 Hz)

2.5

Feedback amplifiers

Feedback amplifier is the most common form of linear oscillators. These circuits have a transistor or an opamp connected in feedback loop with its output fed back to the input through a feedback circuit (a frequency selective circuit for oscillators). For example in the figures below, a feedback path can be seen connecting output to the input.



Page: 16

The feedback maybe negative or positive based on the terminal of the op-amp to which the output is being connected. If itâ ès connected to the negative terminal it is called negative feedback whereas if itâ ès connected to the positive terminal it is called positive feedback.

3

Operational Amplifier

An operational amplifier, also called as op-amp, is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op-amp produces an output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the potential difference between its input terminals. Given below is the circuit symbol for op-amp.

3.1

Characteristics of op-amp

An ideal op-amp is usually considered to have the following properties: Õ • Infinite open-loop gain G = vout /vin

• Infinite input impedance Rin , and so zero input current • Zero input offset voltage

• Infinite voltage range available at the output

• Infinite bandwidth with zero phase shift and infinite slew rate Engineering Knowledge Test


Page: 17 • Zero output impedance Rout • Zero noise

• Infinite Common-mode rejection ratio (CMRR) • Infinite Power supply rejection ratio.

These ideals can be summarized by the two ”golden rules”: 1. The output attempts to do whatever is necessary to make the voltage difference between the inputs zero. 2. The inputs draw no current. Op-amp applications • Used in computers and many embedded system applications. • Used as comparators and voltage level detectors.

• Used as Schmitt trigger, triangle wave oscillators and active filters. • Used as non-inverting and inverting amplifiers.

4

Active Filters

An active filter is a type of analog electronic filter that uses active components such as an amplifier. Amplifiers included in a filter design can be used to improve the performance and predictability of a filter, while avoiding the need for inductors. An amplifier prevents the load impedance of the following stage from affecting the characteristics of the filter. An active filter can have complex poles and zeros without using a bulky or expensive inductor. The shape of the response, the Q-factor and the tuned frequency can often be set with variable resistors. In some active filter circuits, one parameter can be adjusted without affecting the others.

5

Voltage Controlled Oscillator

A voltage-controlled oscillator or VCO is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. Consequently, modulating signals applied to control input may cause frequency modulation (FM) or phase modulation (PM). A VCO may also be part of a phase-locked loop. A voltage-controlled capacitor is one method of making an LC oscillator vary its frequency in response to a control voltage. Any reverse-biased semiconductor diode displays a measure of voltage-dependent capacitance and can be used to change the frequency of an oscillator by varying a control voltage applied to the diode. Special-purpose variable capacitance varactor diodes are available with well-characterized wide-ranging values of capacitance. Such devices are very convenient in the manufacture of voltage-controlled oscillators.



Page: 18

Timers A timer is a specialized type of clock for measuring time intervals. By function timers can be categorized to two main types. A timer which counts upwards from zero for measuring elapsed time is often called a stopwatch whereas a device which counts down from a specified time interval is more usually called a timer or a countdown timer. A simple example for this type is an hourglass. Following figure shows a simple digital timer.

Combinational Circuits In digital circuit theory, combinational logic, also referred to as time-independent logic, is a type of digital logic which is implemented by Boolean circuits, where the output is a pure function of the present input only. Combinational logic is used in computer circuits to perform Boolean algebra on input signals and on stored data. A simple example of such logic is (A+B+C).

Sequential Circuits In digital circuit theory, sequential logic is a type of logic circuit whose output depends not only on the present value of its input signals but on the sequence of past inputs, the input history. It may also be defined as a combinational logic circuit with memory.



Page: 19 Sequential logic is used to construct finite state machines, a basic building block in all digital circuitry, as well as memory circuits and other devices. Virtually all circuits in practical digital devices are a mixture of combinational and sequential logic.

6

Multiplexer

A multiplexer (or mux) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n select lines, which are used to select the input line to be sent to the output. Multiplexers are mainly used to increase the amount of data that can be sent over the network within a certain amount of time and bandwidth. A multiplexer is also called as data selector. Thus, an electronic multiplexer can be considered as a multiple-input, single-output switch. Following figure shows a basic 2X1 Mux.

7

Schmitt Trigger

In electronics, a Schmitt trigger is a comparator circuit with hysteresis, implemented by applying positive feedback to the non-inverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input signal to a digital output signal. The circuit is named a ”trigger” because the output retains its value until the input changes sufficiently to trigger a change. In the non-inverting configuration, when the input is higher than a certain chosen threshold, the output is high. When the input is below a different (lower) chosen threshold, the output is low, and when the input is between the two levels, the output retains its value. This dual threshold action is called hysteresis and implies that the Schmitt trigger possesses memory and can act as a bistable circuit.



Page: 20

8

Multi-vibrators

A multi-vibrator is an electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops. It is characterized by two amplifying devices (transistors, electron tubes or other devices) cross-coupled by resistors or capacitors. There are three types of multi-vibrators. They are discussed below. • Astable, in which the circuit is not stable in either state, i.e. it continually switches from one state to the other. It functions as a relaxation oscillator. • Monostable, in which one of the states is stable, but the other state is unstable (transient). A trigger pulse causes the circuit to enter the unstable state. After entering the unstable state, the circuit will return to the stable state after a set time. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a one shot. • Bistable, in which the circuit is stable in both the states. It can be flipped from one state to the other by an external trigger pulse. This circuit is also known as a flip flop. It can be used to store one bit of information.

9

Sample and Hold Circuits

A sample and hold (S/H, also ”follow-and-hold”) circuit is an analog device that samples (converts continuous signal to discrete signal) the voltage of a continuously varying analog signal and holds (locks, freezes) its value at a constant level for a specified minimum period of time. Sample and hold circuits are the elementary analog



Page: 21 memory devices. They are typically used in analog-to-digital converters to eliminate variations in input signal that can corrupt the conversion process.

10

Analog to Digital Convertors

An analog-to-digital converter (ADC, A/D, or A to D) is a device that converts a continuous physical quantity (usually voltage) to a digital number that represents the quantity’s amplitude. The conversion involves quantization of the input, so it necessarily introduces a small amount of error. Instead of doing a single conversion, an ADC often performs the conversions (”samples” the input) periodically. The result is a sequence of digital values that have been converted from a continuous-time and continuous-amplitude analog signal to a discrete-time and discrete-amplitude digital signal. An ADC is defined by its bandwidth (the range of frequencies it can measure) and its signal to noise ratio (how accurately it can measure a signal relative to the noise it introduces).

11

Digital to Analog Convertors

A digital-to-analog converter (DAC, D/A, D2A or D-to-A) is a function that converts digital data (usually binary) into an analog signal (current, voltage, or electric charge). Unlike analog signals, digital data can be transmitted, manipulated and stored without degradation, though with more complex equipment. But a DAC is needed to convert the digital signal to analog to drive an earphone or loudspeaker amplifier in order to produce sound (analog air pressure waves). DACs and their inverse, ADCs, are part of an enabling technology that has contributed greatly to the digital revolution. To illustrate, consider a typical long-distance telephone call. The caller’s voice is converted into an analog electrical signal by a microphone and then the analog signal is converted to a digital stream by an ADC. The digital stream is then divided into packets where it may be mixed with other digital data, not necessarily audio. The digital packets are then sent to the destination, but each packet may take a completely different route and may not even arrive at the destination in the correct time order. The digital voice data is then extracted from the packets and assembled into a digital data stream. A DAC converts this into an analog electrical signal, which drives an audio amplifier, which in turn drives a loudspeaker, which finally produces sound.



Page: 22

12

8-bit Microprocessors

In computer architecture, 8-bit integers, memory addresses or other data units are those that are at most 8 bits (1 octet) wide. Also, 8-bit CPU and ALU architectures are those that are based on registers, address buses or data buses of that size. 8-bit is also a term given to a generation of microcomputers in which 8-bit microprocessors were the norm. There are 28 (256) different possible values for 8 bits. When unsigned, it has possible values ranging from 0 to 255, when signed, it has -128 to 127. Eight-bit CPUs use an 8-bit data bus and can therefore access 8 bits of data in a single machine instruction. The address bus is typically a double octet wide (i.e. 16-bit), due to practical and economical considerations. This implies a direct address space of only 64 KB on most 8-bit processors.

12.1

Architecture of 8051 microprocessor

Programming The processor has seven 8-bit registers accessible to the programmer, named A, B, C, D, E, H, and L, where A is the 8-bit accumulator and the other six can be used as independent byte-registers or as three 16-bit register pairs, BC, DE, and HL, depending on the particular instruction. Some instructions use HL as a (limited) 16-bit accumulator. It also has a 16-bit program counter and a 16-bit stack pointer to memory. Instructions such as PUSH PSW and POP PSW affected the Program Status Word (flags). The accumulator stores the results of arithmetic and logical operations and the flags register bits (sign, zero, auxiliary carry, parity and carry flags) are set or cleared according to the results of these operations. Flag register is used to indicate the status of the result for e.g., if the result is positive or negative (sign), if result is zero or non-zero, if there was any carry or stack overflow et cetera.

Interfacing Interfacing of an 8 bit microprocessor depends on the address bus and the device it is being interfaced with. Microprocessors generate parallel outputs i.e. they release 8 bits at once but microcontrollers operate on serial outputs. Thus for the two to be interfaced a conversion circuit will be required that can convert parallel data into serial data and vice-versa. The combination of RS 232 and MAX 232 is popular for such conversion.




'

Analog'Electronics'MCQs!

'

Analog'Electronics'MCQs' 1.'''The'emitter'of'a'transistor'is'generally'doped'the'heaviest'because'it'

'

(a)' has'to'dissipate'maximum'power' (b)' has'to'supply'the'charge'carriers' (c)' is'the'first'region'of'the'transistor'''''''(d)' has'to'supply'the'charge'carriers'

2.'''In'a'properly'biased'NFPFN'transistor,'most'of'the'electrons'from'the'emitter'

'

(a)' pass'to'the'collector'through'the' base' (c)' recombine'with'holes'in'emitter' itself'

(b)' recombine'with'the'holes'in'base' (d)' are'stopped'buy'the'function'barrier'

3.'''In'a'NFPFN'transistor,'the'leakage'current'is'due'to'

'

(a)' flow'of'minority'carriers'from' (b)' flow'of'holes'from'base'to'emitter' collector'to'emitter' ' (c)' flow'of'electrons'from'collector'to'' (d)' flow'of'holes'from'collector'to'base' base'

4.'''In'a'transistor,'the'reverse'saturation'current'!"# '

'

(a)' double'for'every'10'°'rise'in' temperature' (c)' increases'linearly'with' temperature'

(b)' doubles'for'every'1'°'rise'in' temperature' (d)' decreases'linearly'with'temperature'

5.'''The'phenomenon'known'as'“early'effect”'in'a'bipolar'transistor'refers'to'a'reduction' of'the'effective'baseFwidth'caused'by' (a)' ElectronFhole'recombination'at' the'base' (c)' The'forward'biasing'of'the' emitterFcollector'junction' ' '

'

(b)' The'reverse'biasing'of'the'baseF collector'junction' (d)' The'early'removal'of'stored'base' charge'during'saturation'to'cutoff' switching'


'


'

6.''The'transistor'configuration'which'provides'highest'output'impedance'is' ' (a)' common'base' (b)' common'emitter' (c)' common'collector' (d)' none'of'the'above' ' 7.''When'a'transistor'is'used'in'switching'mode'then'what'is'the'turnFon'time?'

'

(a)' sum'of'delay'time'and'rise'time' (c)' sum'of'delay'time'and'storage' time'

(b)' sum'of'rise'time'and'storage'time' (d)' sum'of'rise'time'and'fall'time'

8.''An'ideal'amplifier' (a)' has'+ve'feedback' (c)' has'infinite'voltage'gain' '

(b)' gives'uniform'frequency'response' (d)' responds'only'to'signals'at'its'input' terminals'

9.'''The'action'of'a'JFET'in'its'equivalent'circuit'can'best'be'represented'as'a'' (a)' Current'controlled'current'source' (b)' Current'controlled'voltage'source' (c)' Voltage'controlled'voltage'source' (d)' Voltage'controlled'current'source' ' 10.''Compared'to'the'bipolar'junction'transistor,'a'JFET:' 1.! Has'a'larger'gain'bandwidth'production' 2.! Is'less'noisy' 3.! Has'less'input'resistance' 4.! Current'flow'due'to'minority'carriers' Which'of'the'statements'given'above'are'correct?'

' '

(a)' 1'and'4' (c)' 3'and'4'

(b)' 2'and'3' (d)' 1'and'2' '


'


'

11.'''A'FET' (a)' Incorporates'a'forwardFbiased' junction' (c)' Depends'on'the'variation'of'a' magnetic'field'for'its'operation'

(b)' Uses'a'highFconcentration'emitter' junction' (d)' Depends'on'the'variation'of'the' depletion'layer'width'with'reverse' voltage'for'its'operation'

' 12.'''NFchannel'FETs'are'superior'to'PFchannel'FETs'because'they'have' (a)' lower'switching'time' (c)' higher'input'impedance'

(b)' lower'pinchFoff'voltage' (d)' mobility'of'electrons'in'NFchannel'is' greater'than'mobility'of'holes'in'PF channel'

' 13.'''The'shape'of'the'transfer'characteristic'of'JFET'is'very'nearly'a''

'

(a)' hyperbola'' (c)' parabola'

(b)' straight'line' (d)' none'of'the'above'

14.''In'a'JFET,'drain'current'is'primarily'controlled'by' (a)' size'of'depletion'region' (c)' gate'reverse'bias'

(b)' channel'resistance' (d)' voltage'drop'across'channel'

' 15.''JFET'has'main'drawback'of'

'

(a)' having'low'input'impedance' (c)' being'noisy'

(b)' having'high'output'impedance' (d)' having'small'gainFbandwidth''product'

' 16.''MOSFET'can'be'used'as'a''

' '

(a)' current'controlled'capacitor' (c)' current'controlled'induction' '

(b)' voltage'controlled'capacitor' (d)' voltage'controlled'inductor'


'


'

17.''Consider'the'following'statements' 1.! BJP'is'a'current'controlled'device'with'a'high'input'impedance'and'high'gain' bandwidth' 2.! FET'is'a'voltage'controlled'device'with'high'input'impedance'and'low'gain' bandwidth' 3.! UJT'is'a'negative'resistance'device'and'can'be'used'as'an'oscillator' 4.! BJT,'FET'and'UJT'can'all'be'used'for'amplification' Which'of'the'statements'given'above'are'correct?' (a)' 1'and'2' (c)' 3'and'4'

(b)' 2'and'3' (d)' 1'and'4'

' 18.'The'lower'turn'off'time'of'MOSFET'when'compared'to'BJT'can'be'attributed'to' which'one'of'the'following?'

'

(a)' Input'impedance' (c)' Absence'of'minority'carriers'

(b)' Positive'temperature'coefficient' (d)' OnFstate'resistance'

Answer'(c)' 19.''What'is'the'effect'of'cascading'the'amplifier'stages?'

'

(a)' To'increase'the'voltage'gain'and' increase'the'bandwidth' (c)' To'decrease'the'voltage'gain'and' increase'the'bandwidth'

(b)' To'increase'the'voltage'gain'and' reduce'the'bandwidth' (d)' To'decrease'the'voltage'gain'and' reduce'the'bandwidth'

20.''The'major'advantage'of'dc'amplifiers'is'that'it'

' '

(a)' uses'less'number'of'components' (c)' does'not'use'frequency'sensitive' stability' '

(b)' has'very'good'temperature'stability' (d)' can'amplify'direct'current'and'low' frequency'signals'


'


'

21.'''The'output'power'of'a'power'amplifier'is'several'times'its'input'power.'This'is' possible'due'to'the'fact'that'

'

(a)' step'up'transformer'is'used'in'the' (b)' there'is'a'positive'feedback'in'the' circuit' circuit' (c)' a'negative'resistance'is' (d)' power'amplifier'converts'a'part'of' introduced' the'input'dc'power'into'ac'power'

22.'''The'type'of'power'amplifier'which'exhibits'crossover'distortion'in'its'output'is'

'

(a)' class'A' (c)' class'AB'

(b)' class'B' (d)' class'C'

23.'''In'a'feedback'amplifier,'the'feedback'improves'the'signal'to'noise'ratio'for'noise' signal'

'

(a)' present'with'the'amplifier' (c)' internally'generated'in'the' amplifier'

(b)' present'at'the'output' (d)' both'internally'generated'and' present'with'input'

24.'''Feedback'in'amplifier'always'helps'in'

'

(a)' controlling'its'output' (c)' reducing'its'input'impedance'

(b)' increasing'its'gain' (d)' stabilizes'its'gain'

25.'''Consider'the'following'statements' Negative'feedback'in'amplifier'results'in' 1.! Reduced'voltage'gain' 2.! Reduced'bandwidth' 3.! Increases'signal'to'noise'ratio' 4.! Reduced'distortion' Of'these'statements'

'

(a)' 1'and'2'are'correct' (c)' 2,'3'and'4'are'correct'

(b)' 1,'3'and'4'are'correct' (d)' 1'and'4'correct'


'


'

26.'''A'Darlington'amplifier'has'a''

'

(a)' large'current'gain'and'high'input' resistance' (c)' small'voltage'gain'and'low'input' resistance'

(b)' large'voltage'gain'and'low'ouput' resistance' (d)' small'current'gain'and'high'output' resistance'

27.''The'Darlington'pair'is'mainly'used'for'

'

(a)' impedance'matching' (c)' power'amplification'

(b)' wideband'voltage'amplification' (d)' reducing'distortion'

28.''Cascaded'amplifier'are'used'as'

'

(a)' video'amplifier' (c)' power'amplifiers''

(b)' voltage'amplifier' (d)' tuned'amplifier'design'

29.''The'BJT'amplifier'which'offers'highest'input'impedance'and'least'voltage'gain'is'

'

(a)' CE' (c)' CC'

(b)' CB' (d)' Cascade'amplifier'

30.''In'high'frequency'region,'amplifier'will'behave'like'

'

(a)' band'pass'filter' (c)' low'pass'filter'

(b)' high'pass'filter' (d)' none'of'the'above'

31.'''In'signal'generators'

'

(a)' energy'is'created' (b)' energy'is'generated' (c)' energy'is'converted'from'a'simple' (d)' all'of'the'above' dc'source'into'ac'energy'at'some' ' specific'frequency'

32.''The'Barkhausen'criterion'for'sustained'oscillations'is'given'by' (a)' Aβ'='1' (c)' │Aβ│'≤'1'

(b)' │Aβ│'≥'1' (d)' ∠Aβ=180°'


'


'

' 33.''Oscillators'use'following'feedback' (a)' Negative' (c)' Both'negative'and'positive'

(b)' Positive' (d)' '

' 34.'''Crustal'oscillators'are'superior'to'tuned'LC'oscillators'mainly'because'of'their'

'

(a)' high'degree'of'frequency'stability' (b)' size'of'crystal' (c)' high'value'of'Q' (d)' availability'crystal'

35.'''In'a'piezoelectric'crystal'oscillator,'the'oscillation'or'tuning'frequency'is'linearly' proportional'to'the'' (a)' mass'of'the'crystal' (c)' square'of'the'mass'of'the'crystal'

(b)' square'root'of'the'mass'of'the'crystal' (d)' inverse'of'the'square'root'of'the' mass'of'the'crystal'

36.''A'beat'frequency'oscillator'uses' (a)' Two'RF'oscillators' (c)' One'RF'oscillator'

(b)' Two'AF'oscillators' (d)' One'AF'oscillator'

' 37.'''A'triangular'wave'can'be'generated'by'

'

(a)' integrating'a'square'wave' (c)' integrating'a'sine'wave'

(b)' differentiating'a'square'wave' (d)' differentiating'a'sine'wave'

38.'''A'relaxation'oscillator'is'one'which'' (a)' relaxes'indefinitely'' (c)' produces'nonFsinusoidal'waves'

(b)' produces'sinusoidal'waves' (d)' oscillates'continuously'

' 39.''The'multivibrator'circuit'which'possess'one'stable'state'and'one'quasiFstable'is'

'

(a)' astable' (c)' bistable'

(b)' monostable' (d)' Schmitt'trigger'circuit'


'


'

40.'''A'blocking'oscillator'

'

(a)' is'a'triggered'oscillator' (c)' is'an'amplifier'with'a'negative' feedback'

(b)' generates'sinusoidal'waves' (d)' produces'very'sharp'and'narrow' pulses'

41.''The'type'of'multivibrator'used'for'generation'of'clock'pulses'is' (a)' Monostable'multivibrator' (c)' bistable'multivibrator'

(b)' astable'multivibrator' (d)' none'of'the'vibrator'

' 42.'''Schmitt'trigger'is'basically'

'

(a)' an'astable'multivibrator' (c)' a'bistable'multivibrator'

(b)' a'monostable'multivibrator' (d)' an'oscillator'

43.''Most'important'advantage'of'an'IC'is'its'

'

(a)' very'low'cost'' (c)' extremely'small'size'

(b)' extremely'high'reliability' (d)' very'small'weight'

44.''Ultraviolet'radiation'is'used'in'IC'fabrication'process'for'

'

(a)' diffusion' (c)' isolation'

(b)' masking' (d)' metallization'

45.''In'the'context'of'IC'fabrication,'metallization'means' (a)' covering'with'a'metal'cap' (c)' connecting'metal'wires'

(b)' depositing'%&'( layer' (d)' forming'interconnecting'conduction' pattern'and'bounding'pads' 46.'''Why'is'silicon'dioxide'(%&'( )'used'in'ICs?' (a)' To'protect'the'surface'of'the'chip' (b)' Because'it'facilitates'the'penetration' from'external'contaminants'and' of'the'desired'impurity'by'diffusion' to'allow'for'selective'formation'of' ' the'n'and'p'regions'by'diffusion.' (c)' To'control'the'concentration'of' (d)' Because'the'its'high'heat'conduction' the'diffused'impurity' '


'


'

' 47.'''An'operational'amplifier'is'basically'a'' (a)' Low'gain'ac'amplifier' (c)' High'gain'RC'coupled'amplifier' '

(b)' High'gain'dc'amplifier' (d)' Low'gain'transformerFcoupled' amplifier'

48.'''An'ideal'opFamp'is'an'ideal'

'

(a)' Voltage'controlled'current'source' (b)' Voltage'controlled'voltage'source' (c)' Current'controlled'current'source' (d)' Current'controlled'voltage'source'

49.''When'you'apply'a'triangular'waveform'to'the'input'of'a'differentiator,'the'output'is' (a)' a'dc'level' (c)' square'waveform' '

(b)' an'inverted'triangular'waveform' (d)' the'first'harmonic'of'the'triangular' wave'

50.''A'sinusoidal'waveform'can'be'converted'to'a'square'waveform'by'using'a''

'

(a)' two'stage'transistorized' overdriven'amplifier' (c)' voltage'comparator'based'in'opF amp'

(b)' two'stage'diode'detector'circuit' (d)' regenerative'voltage'comparator' circuit'

51.''A'major'advantage'of'active'filters'in'that'they'can'be'realized'without'using'

'

(a)' opFamps' (c)' resistors'

(b)' inductors' (d)' capacitors'

52.'''For'a'step'input,'the'output'of'an'integrator'is'

' '

(a)' a'pulse' (c)' a'spike'

(b)' a'triangular'waveform' (d)' a'ramp' '


'


'

53.''An'oscillator'whose'frequency'is'changed'by'a'variable'dc'voltage,'is'known'as'

'

(a)' a'crystal'oscillator' (c)' an'Armstrong'oscillator'

(b)' a'VCO' (d)' a'piezoelectric'device'

54.''Notch'filter'is'also'called'as'

'

(a)' bandstop'filter' (c)' highFpass'filter'

(b)' lowFpass'filter' (d)' narrowband'reject'filter' Answers:!Analog!Electronics!MCQs!

1.'(b)'

2.'(a)'

3.'(d)'

4.'(a)'

5.'(b)'

6.'(a)'

7.'(a)'

8.'(d)'

9.'(d)'

10.'(c)'

11.'(d)' 12.'(d)' 13.'(a)' 14.'(c)' 15.'(d)' 16.'(b)' 17.'(b)' 18.'(c)' 19.'(b)' 20.'(b)' 21.'(d)' 22.'(b)' 23.'(c)' 24.'(a)' 25.'(d)' 26.'(a)' 27.'(a)' 28.'(c)' 29.'(c)' 30.'(c)' 31.'(c)' 32.'(b)' 33.'(b)' 34.'(a)' 35.'(d)' 36.'(a)' 37.'(a)' 38.'(c)' 39.'(b)' 40.'(d)' 41.'(a)' 42.'(c)' 43.'(b)' 44.'(b)' 45.'(d)' 46.'(a)' 47.'(b)' 48.'(b)' 49.'(c)' 50.'(c)' 51.'(b)' 52.'(d)' 53.'(b)' 54.'(a)' ' '

'

'

'

'

'


'

Digital'Electronics'MCQs'

' Digital'Electronics'MCQs' ! 1.''The'binary'equivalent'of' 11.6275 '( )is' (a)' 101.11011' (b)' 1011.1011' (c)' 101.0011' (d)' 1011.0011' ' 2.''2’s'complement'of'the'number'1010101'is' (a)' 0101010' (b)' 0101011' (c)' 1101010' (d)' 1110011' ' 3.''Multiplication'of'two'binary'numbers'011'and'110'is' (a)' 10010' (b)' 11001' (c)' 11100' (d)' 01110' ' 4.''The'octal'equivalent'of'decimal'98'is' (a)' 89' (b)' 98' (c)' 142' (d)' 241' ' 5.''The'decimal'equivalent'of'the'hexadecimal'number' *+, '- 'is' (a)' 111013' (b)' 5929' (c)' 3416' (d)' 2989' ' 6.''Which'of'the'following'statements'is/are'correct'in'regard'to'excess'3'code?' (a)' It'is'a'BCD'code' (b)' It'is'an'unweighted'code' (c)' It'is'selfRcomplementing'code' (d)' All'of'the'above' ' 7.''BCD'code'is' (a)' a'binary'code' (b)' unweighted'code' (c)' the'same'thing'as'binary'numbers' (d)' the'same'as'gray'code' ' 8.''What'is'the'gray'code'word'for'the'binary'number'101011?' (a)' 101011' (b)' 110101' (c)' 011111' (d)' 111110' ' 9.''Which'one'of'the'following'is'a'nonRvalid'BCD'code?' (a)' 0111'1001' (b)' 0101'1011' (c)' 0100'1000' (d)' 0100'1001' ' 10.'The'number'of'bits'required'to'represent'an'eight'digit'decimal'number'BCD'is'' '


(a)' 8' (c)' 24'

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(b)' 16' (d)' 32'

' 11.'The'ASCII'is'an'input'code' (a)' It'is'a'two'bit'code' (b)' It'is'a'four'bit'code' (c)' It'is'a'seven'bit'code' (d)' It'is'an'eight'bit'code' ' 12.'A'logic'gate'in'an'electronic'circuit'which'' (a)' operates'on'binary'algebra' (b)' performs'arithmetic'and'logic' functions' (c)' allows'flow'of'electrons'only'in' (d)' alternates'between'0'and'1'value' one'direction' ' 13.'Three'Boolean'operators'are' (a)' NOT,'OR,'AND' (b)' NOT,'NAND,'OR' (c)' NOR,'OR,'NOT' (d)' NOR,'NAND,'NOT' ' 14.'The'only'function'of'a'NOT'gate'is'to' (a)' Invert'an'input'signal' (b)' Act'as'a'universal'gate' (c)' Stop'a'signal' (d)' None'of'the'above' ' 15.'The'output'of'a'2Riput'OR'gate'is'zero'only'when'its' (a)' either'input'is'0' (b)' either'input'is'1' (c)' both'inputs'are'1' (d)' both'inputs'are'0' ' 16.'A'combinational'circuit' (a)' always'contains'memory' (b)' never'contains'memory'elements' elements' (c)' may'sometimes'contain'memory' (d)' contains'only'memory'elements' elements' ' 17.'The'output'of'a'AND'gate'is'high'if' (a)' both'inputs'are'low' (b)' one'input'is'high'and'the'other'is'low' (c)' both'inputs'are'high' (d)' none'of'the'above' ' 18.'The'complete'set'of'only'those'Logic'Gates'designed'as'Universal'Gates'is' (a)' NOT,'OR'and'AND'Gates' (b)' XNOR,'NOR'and'NAND'Gates' (c)' NOR'and'NAND'gates' (d)' XOR,'NOR'and'NAND'gates' ' 19.'Consider'the'following'logic'operators:' '


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1.! AND''''''' 2.! OR' 3.! NOT' Their'correct'hierarchy'is' (a)' 1,2,3' (b)' 3,1,2' (c)' 1,3,2' (d)' 2,3,1' ' 20.'In'exclusive'OR'gate,'output'is'zero'when'the'inputs'are' (a)' 0,1' (b)' 1,0' (c)' 1,1' (d)' 1,x' ' 21.'The'output'of'a'logic'gate'is'‘1’'when'all'its'input'are'at'logic'“0”'' The'gate'is'either' (a)' A'NAND'or'an'EXROR'gate' (b)' A'NOR'or'an'EXROR'gate' (c)' An'AND'or'an'EXRNOR'gate' (d)' A'NOR'or'an'EXRNOR'gate' ' 22.'An'XOR'gate'produces'output'only'when'two'inputs'are' (a)' high' (b)' low' (c)' different' (d)' equal' ' 23.'An'AND'gate' (a)' implements'logic'addition' (b)' gives'high'output'only'when'all' inputs'are'low' (c)' is'equivalent'to'a'series'switching' (d)' is'equivalent'to'a'parallel'switching' circuit' circuit' ' ' ' 24.'Which'of'the'following'Boolean'expression'is'‘NOT'TRUE’?' (a)' + + 1 = +' (b)' + + + = 1' (c)' +. + = +' (d)' +. + = 0' ' 25.'Which'of'the'following'Boolean'algebra'rules'is'correct?' (a)' +. + = 1' (b)' + + +* = + + *' (c)' + + +* = + + *' (d)' + + + * = *' ' 26.'The'AND'function'can'be'realized'by'using'‘n’'number'of'NOR'gates.'What'is'‘n’' equal'to?' (a)' 2' (b)' 3' (c)' 4' (d)' 5' '


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' 27.'According'to'DeRMorgan’s'second'theorem' (a)' A'NAND'gate'is'always' (b)' An'AND'gate'is'equivalent'to'a' complementary'to'an'AND'gate' bubbled'NAND'gate' (c)' A'NAND'gate'is'equivalent'to'an' (d)' A'NAND'gate'is'equivalent'to'a' bubbled'AND'gate' bubbled'OR'gate' ' 28.'What'are'the'ultimate'purposes'of'minimizing'logic'expressions?' 1.! To'get'a'small'size'expression' 2.! To'reduce'the'number'of'variables'in'the'given'expression' 3.! To'implement'the'function'of'the'logic'expression'with'least'hardware.' 4.! To'reduce'the'expression'for'making'it'feasible'for'hardware'implementation' Select'the'correct'answer'from'the'codes'given'below' (a)' 1'only' (b)' 2'and'3'only' (c)' 3'only' (d)' 3'and'4'' ' 29.'The'reason'for'using'gray'code'in'kRmaps'is' (a)' gray'code'is'efficient'than'binary' (b)' gray'code'provides'cell'values'that' codes' differ'in'only'one'bit'in'adjacent'cells' (c)' no'other'code'is'available' (d)' any'other'code'can'also'be'used' ' 30.'Consider'the'following' Any'combinational'circuit'can'be'build'using' 1.! NAND'gate' 2.! NOR'gates' 3.! EXROR'gates' 4.! Multipliers' Which'of'these'are'correct?' (a)' 1,'2'and'3' (b)' 1,'3'and'4' (c)' 2,'3'and'4' (d)' 1,'2'and'4' ' 31.'In'a'sequential'circuit,'the'output'state'depends'upon' (a)' past'output'states'and'present' (b)' input'states'only' input'states' (c)' input'and'output'states' (d)' none'of'these' ' 32.'Which'of'the'following'circuits'come'under'the'class'of'combinational'logic'circuits?' 1.! Full'adder' 2.! Full'subtracter' 3.! Half'ladder' '


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4.! JRK'flip' 5.! Counter' Select'the'correct'answer'from'the'codes'given'below' (a)' 1'and'2' (b)' 2'and'3' (c)' 3'and'4' (d)' 4'and'5' ' 33.'A'full'adder'can'be'made'of' (a)' Two'half'adders' (b)' Two'half'adders'and'a'NOR'gate' (c)' Two'half'adders'and'a'OR'gate' (d)' Two'half'adders'and'a'AND'gate' ' 34.'A'gate'is'inhibited'when'its'input'is'at'‘1’.'The'gate'is' (a)' AND' (b)' NAND' (c)' OR' (d)' NOR' ' 35.'Which'of'the'following'flip'flop'is'used'as'a'latch?' (a)' JRK'flipRflop' (b)' RS'flipRflop' (c)' T'flipRflop' (d)' D'flipRflop' ' 36.'The'number'of'flip'flops'required'in'a'decade'counter'is' (a)' 2' (b)' 3' (c)' 4' (d)' 0' ' 37.'The'full'forms'of'the'abbreviations'TTL'and'CMOS'in'reference'to'logic'families'are' (a)' Triple'Transistor'logic'and'Chip' (b)' Tristate'transistor'logic'and'chip' metal'oxide'semiconductor' metal'oxide'semiconductor' (c)' Transistor'Transistor'Logic'and' (d)' Tristate'transistor'logic'and' complementary'metal'oxide' complementary'metal'oxide'silicon' semiconductor' ' 38.'The'logic'circuit'which'belongs'to'nonRsaturated'logic'is' (a)' ECL' (b)' TTL' (c)' CMOS' (d)' NMOS' ' 39.'In'a'CMOS'inverter,' (a)' one'transistor'is'N'channel' (b)' one'transistor'is'N'channel'depletion' depletion'type'and'the'other'is'P' type'and'the'other'is'N'channel' channel'enhancement'type' enhancement'type' (c)' One'transistor'is'N'channel' (d)' One'transistor'is'N'channel' enhancement'type'and'the'other' enhancement'type'and'the'other'is' is'P'channel'enhancement'type' also'N'channel'enhancement'type' '


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' 40.'The'logic'family'which'has'minimum'power'dissipation'is' (a)' 112) (b)' 3 4 2) (c)' 562) (d)' 6789) ' 41.'Among'the'following'four,'the'slowest'ADC'analogRtoRdigital'converter'is' (a)' parallel'comparator'type' (b)' successive'approximation'type' (c)' integrating'type' (d)' counting'type' ' ! ! ! Answers:'Digital'Electronics'MCQs' ! 1.!(b)!

2.!!(b)!

3.!(a)!

4.!(c)!

5.!(d)!

6.!(d)!

7.!(a)!

8.!(d)!

9.!(b)!

10.!(d)!

11.!(c)! 12.!(b)! 13.!(a)! 14.!(a)! 15.!(d)! 16.!(b)! 17.!(c)! 18.!(c)! 19.!(b)! 20.!(c)! 21.!(d)! 22.!(c)! 23.!(c)! 24.!(a)! 25.!(c)! 26.!(b)! 27.!(d)! 28.!(d)! 29.!(b)! 30.!(d)! 31.!(a)! 32.!(d)! 33.!(c)! 34.!(d)! 35.!(d)! 36.!(c)! 37.!(c)! 38.!(a)! 39.!(c)! 40.!(d)! 41.!(c)! ! '

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Electrical Engineering Contents 1 Transformer

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2 Emf Equation of Transformer

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3 Ideal transformer

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4 Losses in a transformer

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5 Transformer tests

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6 Parallel operation of Transformers

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7 Auto Transformer

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8 Induction Motor

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9 Working Principle of Induction Motor

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10 Types Induction Motor

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11 DC 11.1 11.2 11.3 11.4 11.5 11.6 11.7

Motor: Principal production . . . . . . . . . . . . . . . Motoring operation of a d.c. machine . Constructional aspects of dc machines Armature reaction . . . . . . . . . . . Parallel operation of DC generators . . Shunt Generators . . . . . . . . . . . . Speed control of d.c. motors . . . . . .

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Transformer • A transformer is a static machine used for transforming power from one circuit to another without changing frequency. This is a very basic definition of transformer. • A varying current in the transformer’s primary winding creates a varying magnetic flux in the core and a varying magnetic field impinging on the secondary winding. This varying magnetic field at the secondary induces a varying electromotive force (EMF) or voltage in the secondary winding. Making use of Faraday’s Law in conjunction with high magnetic permeability core properties, transformers can thus be designed to efficiently change AC voltages from one voltage level to another within power networks. • Ideal transformer

It is very common, for simplification or approximation purposes, to analyze the transformer as an ideal transformer model as represented in the two images. An ideal transformer is a theoretical, linear transformer that is lossless and perfectly coupled; that is, there are no energy losses and flux is completely confined within the magnetic core.

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Working Principle of Transformer The working principle of transformer is very simple. It depends upon Faradayâ ès law of electromagnetic induction. Actually, mutual induction between two or more winding is responsible for transformation action in an electrical transformer. • Faraday’s laws,

”Rate of change of flux linkage with respect to time is directly proportional to the induced EMF in a conductor or coil”.

Constructional Parts of Transformer The three main parts of a transformer are,


Electrical Engineering

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1. Primary Winding of transformer - which produces magnetic flux when it is connected to electrical source. 2. Magnetic Core of transformer - the magnetic flux produced by the primary winding, that will pass through this low reluctance path linked with secondary winding and create a closed magnetic circuit. 3. Secondary Winding of transformer â the flux, produced by primary winding, passes through the core, will link with the secondary winding. This winding also wounds on the same core and gives the desired output of the transformer.

Leakage Reactance of Transformer • All the flux in transformer will not be able to link with both the primary and secondary windings. A small portion of flux will link either winding but not both. This portion of flux is called leakage flux. • Due to this leakage flux in transformer, there will be a self-reactance in the concerned winding.

• This self-reactance of transformer is alternatively known as leakage reactance of transformer. This self-reactance associated with resistance of transformer is impedance. • Due to this impedance of transformer, there will be voltage drops in both primary and secondary transformer windings.

Resistance of Transformer Generally, both primary and secondary windings of electrical power transformer are made of copper. Copper is a very good conductor of current but not a super conductor. Actually, super conductor and super conductivity both are conceptual, practically they are not available. So both windings will have some resistance. This internal resistance of both primary and secondary windings is collectively known as resistance of transformer.

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Impedance of Transformer

As we said, both primary and secondary windings will have resistance and leakage reactance. These resistance and reactance will be in combination, is nothing but impedance of transformer. If R1 and R2 and X1 and X2 are primary and secondary resistance and leakage reactance of a transformer respectively , then Z1 and Z2 impedance of primary and secondary winding are respectively, Z1 = R1 + jX1 Z2 = R2 + jX2 The Impedance of transformer plays a vital role during parallel operation of transformer.

2

Emf Equation of Transformer E = 4.44„m f T V olts T is number of turns in a winding, „m is the maximum flux in the core in Wb. f = frequency of the AC supply (in Hz)

If E1 and E2 are primary and secondary emfs and T1 and T2 are primary and secondary turns then, voltage ratio or turns ratio of transformer is, E1 4.44„m f T1 T1 = = E2 4.44„m f T2 T2 The transformer winding voltage ratio is thus shown to be directly proportional to the winding turns ratio according to the above equation.



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Ideal transformer • Ideal transformer model is developed by considering a transformer which does not have any loss. That means the windings of the transformer are purely inductive and the core of transformer is loss free. • There is zero leakage reactance of transformer. As we said, whenever we place a low reluctance core inside the windings, maximum amount of flux passes through this core, but still there is some flux which does not pass through the core but passes through the insulation used in the transformer. This flux does not take part in the transformation action of the transformer. This flux is called leakage flux of transformer. • In an ideal transformer, this leakage flux is also considered nil. That means, 100 % flux passes through the core and links with both the primary and secondary windings of transformer. • Although every winding is desired to be purely inductive but it has some resistance in it which causes voltage drop and I 2 R loss in it. In such ideal transformer model, the windings are also considered ideal, that means resistance of the winding is zero.

4

Losses in a transformer

Copper Loss Copper loss is I12 R loss, in primary side and in the secondary side it is I22 R2 , where I1 I2 are primary and secondary current of the transformer and R1 andR2 are the resistances of the primary and secondary winding. Copper loss in transformer vary with load.

Core Losses

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Hysteresis loss and eddy current loss, both depend upon magnetic properties of the materials used to construct the core of transformer and its design. So these losses in transformer are fixed and do not depend upon the load current. So core losses in transformer which is alternatively known as iron loss in transformer can be considered as constant for all range of load. Hysteresis loss in transformer is denoted as, Wh = Kh f (Bm )1.6 watt Eddy current loss in transformer is denoted as, 2 We = ke f 2 Kf2 Bm watts

Where, Kh = Hysteresis constant. Ke = Eddy current constant. Kf = form constant.

Hysteresis Loss The magnetic core of transformer is made of â öCold Rolled Grain Oriented Silicon Steelâ ö. Steel is very good ferromagnetic material. This kind of materials are very sensitive to be magnetized. That means, whenever magnetic flux would pass through, it will behave like magnet. Ferromagnetic substances have numbers of domains in their structure. Domains are very small regions in the material structure, where all the dipoles are paralleled to same direction. In other words, the domains are like small permanent magnets situated randomly in the structure of substance. These domains are arranged inside the material structure in such a random manner, that net resultant magnetic field of the said material is zero. Whenever external magnetic field or mmf is applied to that substance, these randomly directed domains get arranged themselves in parallel to the axis of applied mmf. After removing this external mmf, maximum numbers of domains again come to random positions, but some of them still remain in their changed position. Because of these Engineering Knowledge Test


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unchanged domains, the substance becomes slightly magnetized permanently. This magnetism is called ” Spontaneous Magnetism”. To neutralize this magnetism, some opposite mmf is required to be applied. The magneto motive force or mmf applied in the transformer core is alternating. For every cycle due to this domain reversal, there will be extra work done. For this reason, there will be a consumption of electrical energy which is known as Hysteresis loss of transformer.

Eddy Current Loss In transformer, we supply alternating current in the primary, this alternating current produces alternating magnetizing flux in the core and as this flux links with secondary winding, there will be induced voltage in secondary, resulting current to flow through the load connected with it. Some of the alternating fluxes of transformer; may also link with other conducting parts like steel core or iron body of transformer etc. As alternating flux links with these parts of transformer, there would be a locally induced emf. Due to these emfs, there would be currents which will circulate locally at that parts of the transformer. These circulating current will not contribute in output of the transformer and dissipated as heat. This type of energy loss is called eddy current loss of transformer. This was a broad and simple explanation of eddy current loss. The detail explanation of this loss is not in the scope of discussion in that chapter.

5

Transformer tests

Open Circuit Test The open-circuit test, or ”no-load test”, is one of the methods used in electrical engineering to determine the no-load impedance in the excitation branch of a transformer.

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• The secondary of the transformer is left open-circuited. A wattmeter is connected to the primary. An ammeter is connected in series with the primary winding. A voltmeter is optional since the applied voltage is the same as the voltmeter reading. Rated voltage is applied at primary. • If the applied voltage is normal voltage then normal flux will be set up. Since iron loss is a function of applied voltage, normal iron loss will occur. Hence the iron loss is maximum at rated voltage. This maximum iron loss is measured using the wattmeter. Since the impedance of the series winding of the transformer is very small compared to that of the excitation branch, all of the input voltage is dropped across the excitation branch. Thus the wattmeter measures only the iron loss. This test only measures the combined iron losses consisting of the hysteresis loss and the eddy current loss. Although the hysteresis loss is less than the eddy current loss, it is not negligible. The two losses can be separated by driving the transformer from a variable frequency source since the hysteresis loss varies linearly with supply frequency and the eddy current loss varies with the square.



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• Since the secondary of the transformer is open, the primary draws only no-load current, which will have some copper loss. This no-load current is very small and because the copper loss in the primary is proportional to the square of this current, it is negligible. There is no copper loss in the secondary because there is no secondary current. • Current, voltage and power are measured at the primary winding to ascertain the admittance and power-factor angle. • Another method of determining the series impedance of a real transformer is the short circuit test.

Short circuit test

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Method The test is conducted on the high-voltage (HV) side of the transformer where the low-voltage (LV) side or the secondary is short circuited. The supply voltage required to circulate rated current through the transformer is usually very small and is of the order of a few percent of the nominal voltage and this 5 % voltage is applied across primary. The core losses are very small because applied voltage is only a few percentage of the nominal voltage and hence can be neglected. Thus the wattmeter reading measures only the full load copper loss. Procedure: To conduct a short-circuit test on power transformer: • Isolate the power transformer from service.

• Remove HV/LV jumps and disconnect neutral from earth/ground.

• Short LV phases and connect these short circuited terminals to neutral • Energise HV side by LV supply.

• Measure current in neutral, HV voltage and HV line currents. • Wattmeter indicate total cu loss of the transformer

6

Parallel operation of Transformers

It is economical to install a number of smaller rated transformers in parallel than installing a bigger rated electrical power transformers. This has mainly the following advantages,



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Advantages • To maximize electrical power system efficiency: Generally electrical power transformer gives the maximum efficiency at full load. If we run numbers of transformers in parallel, we can switch on only those transformers which will give the total demand by running nearer to its full load rating for that time. When load increases, we can switch none by one other transformer connected in parallel to fulfill the total demand. In this way we can run the system with maximum efficiency. • To maximize electrical power system availability: If numbers of transformers run in parallel, we can shutdown any one of them for maintenance purpose. Other parallel transformers in system will serve the load without total interruption of power. • To maximize power system reliability: if any one of the transformers run in parallel, is tripped due to fault of other parallel transformers is the system will share the load, hence power supply may not be interrupted if the shared loads do not make other transformers over loaded. • To maximize electrical power system flexibility: There is always a chance of increasing or decreasing future demand of power system. If it is predicted that power demand will be increased in future, there must be a provision of connecting transformers in system in parallel to fulfill the extra demand because, it is not economical from business point of view to install a bigger rated single transformer by forecasting the increased future demand as it is unnecessary investment of money. Again if future demand is decreased, transformers running in parallel can be removed from system to balance the capital investment and its return.

Condition for parallel operating Following conditions must be satisfied for a successful operation.

shop.ssb cra ck.com 1. Same voltage ratio of transformer. 2. Same percentage impedance. 3. Same polarity.

4. Same phase sequence. • Same Voltage Ratio

If two transformers of different voltage ratio are connected in parallel with same primary supply voltage, there will be a difference in secondary voltages. Now say the secondary of these transformers are connected to same bus, there will be a circulating current between secondaries and therefore between primaries also. As the internal impedance of transformer is small, a small voltage difference may cause sufficiently high circulating current causing unnecessary extra I 2 R loss.

• Same Percentage Impedance

The current shared by two transformers running in parallel should be proportional to their MVA ratings. Again, current carried by these transformers are inversely proportional to their internal impedance. From these two statements it can be said that, impedance of transformers running in parallel are inversely proportional to their MVA ratings. In other words, percentage impedance or per unit values of impedance should be identical for all the transformers that run in parallel.

• Same Polarity

Polarity of all transformers that run in parallel, should be the same otherwise huge circulating current that flows in the transformer but no load will be fed from these transformers. Polarity of transformer means the instantaneous direction of induced emf in secondary. If the instantaneous directions of induced secondary emf in two transformers are opposite to each other when same input power is fed to both of the transformers, the transformers are said to be in opposite polarity. If the instantaneous directions of induced secondary emf in two transformers are same when same input power is fed to the both of the transformers, the transformers are said to be in same polarity.



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• Same Phase Sequence

The phase sequence or the order in which the phases reach their maximum positive voltage, must be identical for two parallel transformers. Otherwise, during the cycle, each pair of phases will be short circuited. The above said conditions must be strictly followed for parallel operation of transformers but totally identical percentage impedance of two different transformers is difficult to achieve practically, that is why the transformers run in parallel may not have exactly same percentage impedance but the values would be as nearer as possible.

7

Auto Transformer

Auto transformer is kind of electrical transformer where primary and secondary shares same common single winding.

shop.ssb cra ck.com • An autotransformer (sometimes called autostep down transformer) is an electrical transformer with only one winding. The ”auto” (Greek for ”self”) prefix refers to the single coil acting on itself and not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer. • In contrast, an ordinary transformer has separate primary and secondary windings which are not connected. • The winding has at least three taps where electrical connections are made.

• Since part of the winding does ”double duty”, autotransformers have the advantages of often being smaller, lighter, and cheaper than typical dual-winding transformers, • but the disadvantage of not providing electrical isolation. Other advantages of autotransformers include lower leakage reactance, lower losses, lower excitation current, and increased KVA rating. • Copper Savings in Auto Transformer

Now we will discuss the savings of copper in auto transformer comparedto conventional two winding transformer. We know that weight of copper of any winding depends upon its length and cross -sectional area. Again length of conductor in winding is proportional to its number of turns and cross -sectional area varies with rated current. So weight of copper in winding is directly proportional to product of number of turns and rated current of the winding.



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Induction Motor • One of the most common electrical motor used in most applications which is known as induction motor. This motor is also called as asynchronous motor because it runs at a speed less than synchronous speed. In this, we need to define what is synchronous speed. Synchronous speed is the speed of rotation of the magnetic field in a rotary machine and it depends upon the frequency and number poles of the machine. • An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux current in the rotor with flux current in the stator, the rotor will never reach to its rotating magnetic field speed i.e. the synchronous speed. • There are basically two types of induction motor that depend upon the input supply - single phase induction motor and three phase induction motor. Single phase induction motor is not a self starting motor which we will discuss later and three phase induction motor is a self-starting motor. Now in general we need to give two supply i.e. double excitation to make a machine to rotate. For example if we consider a DC motor, we will give one supply to the stator and another to the rotor through brush arrangement.

9

Working Principle of Induction Motor

But in induction motor we give only one supply, so it is really interesting to know that how it works. It is very simple, from the name itself we can understand that there is induction process occurred. Actually when we are giving the supply to the stator winding, flux will generate in the coil due to flow of current in the coil. Now the rotor winding is arranged in such a way that it becomes short circuited in the rotor itself. The flux from the stator will cut the coil in the rotor and since the rotor coils are short circuited, according to Faraday’s law of electromagnetic induction, current will start flowing in the coil of the rotor. When the current will flow, another flux will get generated in the rotor. Now there will be two flux, one is stator flux and another is rotor flux and the rotor flux will be lagging to the stator flux. Due to this, the rotor will feel a torque which will make the rotor to rotate in the direction of rotating magnetic flux. So the speed of the rotor will be depending upon the ac supply and the speed can be controlled by varying the input supply. This is the working principle of an induction motor of either type.

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10

Types Induction Motor

• Phase induction motor 1. Split phase induction motor 2. Capacitor start induction motor 3. Capacitor start capacitor run induction motor 4. Shaded pole induction motor • Three Phase Inductor Motor 1. Squirrel cage induction motor 2. Slip ring induction motor Single Phase Induction Motor is not Self Starting Three Phase Induction Motor Self Starting

11

DC Motor: Principal

D.C. machines are the electro mechanical energy converters which work from a d.c. source and generate mechanical power or convert mechanical power into a d.c. power. Engineering Knowledge Test


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11.1

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production

When the armature is loaded, the armature conductors carry currents. These current carrying conductors interact with the field and experience force acting on the same. This force is in such a direction as to oppose their cause which in the present case is the relative movement between the conductors and the field. Thus the force directly opposes the motion. Hence it absorbs mechanical energy. This absorbed mechanical power manifests itself as the converted electrical power.

11.2

Motoring operation of a d.c. machine

In the motoring operation the d.c. machine is made to work from a d.c. source and absorb electrical power. This power is converted into the mechanical form. This is briefly discussed here. If the armature of the d.c. machine which is at rest is connected to a d.c. source then, a current flows into the armature conductors. If the field is already excited then these current carrying conductors experience a force as per the law of interaction discussed above and the armature experiences a torque. If the restraining torque could be neglected the armature starts rotating in the direction of the force. The conductors now move under the field and cut the magnetic flux and hence an induced emf appears in them. The polarity of the induced emf is such as to oppose the cause of the current which in the present case is the applied voltage. Thus a ’back emf’ appears and tries to reduce the current. As the induced emf and the current act in opposing sense the machine acts like a sink to the electrical power which the source supplies. This absorbed electrical power gets converted into mechanical form. Thus the same electrical machine works as a generator of electrical power or the absorber of electrical power depending upon the operating condition. The absorbed power gets converted into electrical or mechanical power.

11.3

Constructional aspects of dc machines

1. Body

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The body constitutes the outer shell within which all the other parts are housed. This will be closed at both the ends by two end covers which also support the bearings required to facilitate the rotation of the rotor and the shaft. Even though for the generation of an emf in a conductor a relative movement between the field and the conductor would be enough, due to practical considerations of commutation, a rotating conductor configuration is selected for d.c. machines. Hence the shell or frame supports the poles and yoke of the magnetic system. In many cases the shell forms part of the magnetic circuit itself. Cast steel is used as a material for the frame and yoke as the flux does not vary in these parts. In large machines these are fabricated by suitably welding the different parts. Those are called as fabricated frames. Fabrication as against casting avoids expensive patterns. In small special machines these could be made of stack of laminations suitably fastened together to form a solid structure.

2. Main poles Solid poles of fabricated steel with seperate/integral pole shoes are fastened to the frame by means of bolts. Pole shoes are generally laminated. Sometimes pole body and pole shoe are formed from the same laminations. Stiffeners are used on both sides of the laminations. Riveted through bolts hold the assembly together. The pole shoes are shaped so as to have a slightly increased air gap at the tips. 3. Inter-poles These are small additional poles located in between the main poles. These can be solid, or laminated just as the main poles. These are also fastened to the yoke by bolts. Sometimes the yoke may be slotted to receive these poles. The inter poles could be of tapered section or of uniform cross section. These are also called as commutating poles or compoles. The width of the tip of the compole can be about a rotor slot pitch. 4. Armature The armature is where the moving conductors are located. The armature is constructed by stacking laminated sheets of silicon steel. Thickness of these lamination is kept low to reduce eddy current losses. As the laminations carry alternating flux the choice of suitable material, insulation coating on the laminations, stacking it etc are to be done more carefully. The core is divided into packets to facilitate ventilation. The winding cannot be placed on the surface of the rotor due to the mechanical



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forces coming on the same. Open parallel sided equally spaced slots are normally punched in the rotor laminations. These slots house the armature winding. Large sized machines employ a spider on which the laminations are stacked in segments. End plates are suitably shaped so as to serve as ’Winding supporters’. Armature construction process must ensure provision of sufficient axial and radial ducts to facilitate easy removal of heat from the armature winding. 5. Field windings In the case of wound field machines (as against permanent magnet excited machines) the field winding takes the form of a concentric coil wound around the main poles. These carry the excitation current and produce the main field in the machine. Thus the poles are created electromagnetically. Two types of windings are generally employed. In shunt winding large number of turns of small section copper conductor is used. The resistance of such winding would be an order of magnitude larger than the armature winding resistance. In the case of series winding a few turns of heavy cross section conductor is used. The resistance of such windings is low and is comparable to armature resistance. Some machines may have both the windings on the poles. The total ampere turns required to establish the necessary flux under the poles is calculated from the magnetic circuit calculations. The total mmf required is divided equally between north and south poles as the poles are produced in pairs. The mmf required to be shared between shunt and series windings are apportioned as per the design requirements. As these work on the same magnetic system they are in the form of concentric coils. Mmf ’per pole’ is normally used in these calculations. 6. Armature winding As mentioned earlier, if the armature coils are wound on the surface of the armature, such construction becomes mechanically weak. The conductors may fly away when the armature starts rotating. Hence the armature windings are in general pre-formed, taped and lowered into the open slots on the armature. In the case of small machines, they can be hand wound. The coils are prevented from flying out due to the centrifugal forces by means of bands of steel wire on the surface of the rotor in small groves cut into it. In the case of large machines slot wedges are additionally used to restrain the coils from flying away. The end portion of the windings are taped at the free end and bound to the winding carrier ring of the armature at the commutator end. The armature must be dynamically balanced to reduce the centrifugal forces at the operating speeds

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7. Compensating winding One may find a bar winding housed in the slots on the pole shoes. This is mostly found in d.c. machines of very large rating. Such winding is called compensating winding. In smaller machines, they may be absent. The function and the need of such windings will be discussed later on. 8. Commutator Commutator is the key element which made the d.c. machine of the present day possible. It consists of copper segments tightly fastened together with mica/micanite insulating separators on an insulated base. The whole commutator forms a rigid and solid assembly of insulated copper strips and can rotate at high speeds. Each commutator segment is provided with a ’riser’ where the ends of the armature coils get connected. The surface of the commutator is machined and surface is made concentric with the shaft and the current collecting brushes rest on the same. Under-cutting the mica insulators that are between these commutator segments has to be done periodically to avoid fouling of the surface of the commutator by mica when the commutator gets worn out. 9. Brush Brushes rest on the surface of the commutator. Normally electro-graphite is used as brush material. The actual composition of the brush depends on the peripheral speed of the commutator and the working voltage. The hardness of the graphite brush is selected to be lower than that of the commutator. When the brush wears out the graphite works as a solid lubricant reducing frictional coefficient. More number of relatively smaller width brushes are preferred in place of large broad brushes

11.4

Armature reaction

The interaction between the fields must therefore must be properly understood in order to understand the behavior of the loaded machine. As the magnetic structure is complex and as we are interested in the flux cut by the conductors, we primarily focus our attention on the surface of the armature. A sign convention is required for mmf as the armature and field mmf are on two different members of the machine. The convention used here is that the mmf acting across the air gap and the flux density in the air gap are shown as positive when they act in a direction from the field system to the armature. A flux line is taken and the value of the Engineering Knowledge Test


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current enclosed is determined. As the magnetic circuit is non-linear, the field mmf and armature mmf are separately computed and added at each point on the surface of the armature. The actual flux produced is proportional to the total mmf and the permeance. The flux produced by field and that produced by armature could be added to get the total flux only in the case of a linear magnetic circuit.

11.5

Parallel operation of DC generators

D.C. generators are required to operate in parallel supplying a common load when the load is larger than the capacity of any one machine. In situations where the load is small but becomes high occasionally, it may be a good idea to press a second machine into operation only as the demand increases. This approach reduces the spare capacity requirement and its cost. In cases where one machine is taken out for repair or maintenance, the other machine can operate with reduced load. In all these cases two or more machines are connected to operate in parallel.

11.6

Shunt Generators

Parallel operation of two shunt generators is similar to the operation of two storage batteries in parallel. In the case of generators we can alter the external characteristics easily while it is not possible with batteries. Before connecting the two machines the voltages of the two machines are made equal and opposing inside the loop formed by the two machines. This avoids a circulating current between the machines. The circulating current produces power loss even when the load is not connected. In the case of the loaded machine the difference in the induced emf makes the load sharing unequal.

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11.7

Speed control of d.c. motors

• In the case of speed control, armature voltage control and flux control methods are available. The voltage control can be from a variable voltage source like Ward-Leonard arrangement or by the use of series armature resistance. Unlike the starting conditions the series resistance has to be in the circuit throughout in the case of speed control. That means considerable energy is lost in these resistors. Further these resistors must be adequately cooled for continuous operation. The variable voltage source on the other hand gives the motor the voltage just needed by it and the losses in the control gear is a minimum. This method is commonly used when the speed ratio required is large, as also the power rating. • Field control or flux control is also used for speed control purposes. Normally field weakening is used. This causes operation at higher speeds than the nominal speed. Strengthening the field has little scope for speed control as the machines are already in a state of saturation and large field mmf is needed Engineering Knowledge Test


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for small increase in the flux. Even though flux weakening gives higher speeds of operation it reduces the torque produced by the machine for a given armature current and hence the power delivered does not increase at any armature current. The machine is said to be in constant power mode under field weakening mode of control. Above the nominal speed of operation, constant flux mode with increased applied voltage can be used; but this is never done as the stress on the commutator insulation increases. • Thus operation below nominal speed is done by voltage control. Above the nominal speed field weakening is adopted. For weakening the field, series resistances are used for shunt as well as compound motors. In the case of series motors however field weakening is done by the use of ’diverters’ . Diverters are resistances that are connected in parallel to the series winding to reduce the field current without affecting the armature current.

Braking the d.c. motors When a motor is switched off it â Ÿcoastsâ è to rest under the action of frictional forces. Braking is employed when rapid stopping is required. In many cases mechanical braking is adopted. The electric braking may be done for various reasons such as those mentioned below: 1. 2. 3. 4. 5.

To augment the brake power of the mechanical brakes. To save the life of the mechanical brakes. To regenerate the electrical power and improve the energy efficiency. In the case of emergencies to step the machine instantly. To improve the through put in many production process by reducing the stopping time.

Basically the electric braking involved is fairly simple. The electric motor can be made to work as a generator by suitable terminal conditions and absorb mechanical energy. This converted mechanical power is dissipated/used on the electrical network suitably. Braking can be broadly classified into 1. Dynamic 2. Regenerative 3. Reverse voltage braking or plugging

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Electrical'Engineering'MCQs'

Electrical)Engineering)MCQs) DC)Machines) ! 1.''What'is'the'effect'produced'by'the'electric'current'in'an'electrical'motor?' (a)' Magnetic'effect' (b)' Magnetic'as'well'as'heating'effect' (c)' Heating'effect'only' (d)' Heating'as'well'as'chemical'effect' ' 2.''The'rotating'part'of'a'dc'motor'is'known'as' (a)' Pole'stator' (b)' Stator' (c)' Armature' (d)' Carbon'brush' ' 3.''The'function'of'the'commutator'in'a'dc'motor'machine'is' (a)' To'change'direct'current'to' (b)' To'improve'commutation' alternate'current' (c)' For'easy'speed'control' (d)' to'change'alternating'voltage'to' direct'voltage' ' 4.''Carbon'brushes'are'used'in'electric'motor'to' (a)' Brush'off'carbon'deposits'on'the' (b)' Provide'a'path'for'flow'of'current' commutator' (c)' Prevent'overheating'of'armature' (d)' Prevent'sparking'during' winding' commutation' ' 5.''Voltage'equation'for'dc'motor'is' (a)' ! = #$ + &' (' ' (b)' ! = #$ − &' (' ' (c)' #$ = ! + &' (' ' (d)' #$ = 0.5&' (' ' ' 6.''The'speed'of'a'd.c'motor'is' (a)' Directly'proportional'to'back'emf' (b)' Inversely'proportional'to'back'emf' and'inversely'proportional'to'flux' and'directly'proportional'to'flux' (c)' Directly'proportional'to'emf'as' (d)' Inversely'proportional'to'emf'as'well' well'as'flux' as'flux' ' 7.''In'a'dc'motor'the'iron'losses'occur'in' (a)' The'yoke' (b)' The'armature' (c)' The'field' (d)' None'of'these' ' 8.''The'function'of'the'starter'in'dc'machines'is' (a)' To'avoid'the'excessive'current'at' (b)' To'control'the'speed' starting' '


(c)' To'avoid'armature'reaction'

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(d)' To'avoid'excess'heating'

' 9.''An'external'resistance'added'in'the'field'of'a'd.c'shunt'generator'will' (a)' Increase'the'speed'of'the' (b)' Increase'the'voltage'of'the'generator' generator' (c)' Decrease'the'voltage'of'the' (d)' Increase'the'power'delivered' generator' ' 10.'The'current'flowing'in'the'conductor'of'a'd.c'motor'is' (a)' a.c' (b)' d.c' (c)' a.c'as'well'as'd.c' (d)' transient' ' 11.''The'torque'of'a'motor'is' (a)' Force'in'NYm'acting'on'the'motor' (b)' The'product'of'tangential'force'on' the'rotor'and'its'radius' (c)' The'power'in'KW' (d)' The'power'given'to'load'being'driven' by'the'motor' 12.'The'output'power'of'any'electrical'motor'is'taken'from' (a)' The'armature' (b)' The'coupling'mounted'on'the'shaft' (c)' The'conductor' (d)' The'poles' ' 13.'The'power'stated'on'the'name'plate'of'any'motor'is'always' (a)' The'output'power'of'any'shaft' (b)' The'power'drawn'in'kVA' (c)' The'power'drawn'in'kW' (d)' The'gross'power' ' 14.'The'armature'of'd.c'motors'is'laminated' (a)' To'reduce'the'hysteresis'lossess' (b)' To'reduce'eddy'current'losses' (c)' To'reduce'the'inductivity'of' (d)' To'reduce'the'mass'of'the'armature' armature' ' 15.'The'speed'of'a'series'motor'at'no'load'is' (a)' Zero' (b)' 3000'rpm' (c)' 3600'rpm' (d)' Infinity' ' 16.'The'speed'of'dc'series'motor'decreases'if'the'flux'in'the'field'winding' (a)' Remains'constant' (b)' Increases' (c)' Decreases' (d)' None'of'these' ' 17.'D.C'series'motors'are'best'suited'for'traction'work'because' (a)' Torque'is'proportional'to'the' (b)' Torque'is'proportional'to'the'square' '


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square'of'armature'current'and' of'armature'current'and'speed'in' speed'in'inversely'proportional'to' directly'proportional'to'torque' torque' (c)' Torque'and'speed'are' (d)' None'of'these' proportional'to'square'of' ' armature'current' ' 18.'A'series'motor'is'started'without'load.'The'effect'is'that' (a)' The'torque'increases'rapidly' (b)' The'speed'increases'rapidly' (c)' Current'drawn'increases'rapidly' (d)' The'back'emf'decreases' ' 19.'The'direction'of'rotation''a'D.C'series'motor'can'be'reversed'by'interchanging' (a)' The'supply'terminals'only' (b)' The'field'terminals'only' (c)' The'supply'as'well'as'field' (d)' None'of'these' terminals' ' 20.'Armature'reaction'is'attributed'to' (a)' The'effect'of'magnetic'field'setup' (b)' The'effect'of'magnetic'field'setup'by' to'armature'current' field'current' (c)' Copper'loss'in'the'armature' (d)' The'effect'of'magnetic'field'setup'by' back'emf' ' 21.'Which'of'the'following'dc'motors'is'suitable'for'high'starting'torque?' (a)' Shunt'motor' (b)' Commutative'compound'motor' (c)' Series'motor' (d)' Compound'motor' ' 22.'As'the'load'is'increased,'the'speed'of'a'shunt'motor' (a)' Remains'constant' (b)' Increases'slightly' (c)' Reduces'slightly' (d)' None'of'these' ' 23.'For'parallel'operation,'the'polarities'of'two'generators' (a)' Must'oppose'each'other' (b)' Must'be'same' (c)' May'or'may'not'be'same' (d)' None'of'these' ' 24.'The'emf'induced'in'the'armature'of'a'd.c'machine'is' (a)' Directly'proportional'to'the'flux' (b)' directly'proportional'to'both'flux'and' and'inversely'proportional'to'the' the'speed' speed' ' (c)' inversely'proportional'to'both'the' (d)' none'of'the'above' flux'and'the'speed' ' '


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' 25.'The'direction'of'induction'emf'in'an'armature'coil'of'a'dc'machine'is' (a)' The'same'as'that'of'the'current' (b)' Opposite'to'that'of'the'current'for' for'both'the'generator'and'the' both'the'generator'and'the'motor' motor' (c)' The'same'as'that'of'the'current' (d)' None'of'these' for'the'generator'and'opposite'to' ' that'of'the'current'for'the'motor' ' 26.'The'commutator'of'machine'acts'as'a' (a)' FullYwave'rectifier' (b)' HalfYwave'rectifier' (c)' Controlled'fullYwave'rectifier' (d)' Controlled'halfYwave'rectifier' ' 27.'Consider'the'following'statement' ' I.'''The'purpose'of'using'of'compensating'winding'in'a'd.c'machine'is'to'counteract' II.''Armature'reaction'm.m.f'under'the'poleYfaces.' III.'Armature'reaction'm.m.m'in'the'interpole'zone.' IV.Flashover'between'positive'and'negative'brushes.' ' State'which'of'the'following'is'correct.' (a)' Both'I'and'II' (b)' Only'III' (c)' Both'I'and'III' (d)' Both'II'and'III' ' 28.'The'core'losses'in'a'd.c'machine'occur'due'to' (a)' Hysteresis'only' (b)' Eddy'current'only' (c)' Armature'current'' (d)' Both'hysteresis'and'eddy'currents' ' 29.'The'core'losses'in'a'd.c'machine'occur'in' (a)' The'armature'only' (b)' The'pole'faces'only' (c)' The'yoke'only' (d)' Both'the'armature'and'the'pole'faces' ' 30.'Ohmic'losses'in'a'd.c'machine'occur'in' (a)' The'armature'winding'only' (b)' The'field'winding'only' (c)' The'brush'contact'only' (d)' The'armature'winding,'the'field' winding'and'also'the'variable'losses' is'equal'to.' ' 31.'The'brake'test'for'the'determination'of'efficiency'of'a'd.c'machine'is' (a)' An'indirect'method' (b)' A'regenerative'method' '


(c)' A'direct'method'

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(d)' None'of'these'

' 32.'In'Swinburne’s'method'for'the'determination'of'efficiency'of'a'd.c'machine' (a)' The'noYload'losses'are'calculated' (b)' The'noYload'losses'and'measured' and'the'copper'losses'are' copper'losses'are'calculated' measured' (c)' Both'the'noYload'losses'and'the' (d)' Both'the'noYload'losses'and'copper' copper'losses'are'measured' losses'are'calculated' ' ' 33.'In'the'Kapp’s'modification'of'Hopkinson’s'efficiency'test' (a)' The'power'losses'in'the'two' (b)' The'power'output'of'the'generator'is' machines'are'supplied' dissipated'in'a'resistor' mechanically' (c)' The'two'machines'are' (d)' The'power'losses'in'the'two' mechanically'decoupled' machines'are'supplied'electrically' ' 34.'For'dc'shunt'motor,'speed'control'by'armature'resistance'variations'is'best'suited' for' (a)' Constant'power'drive' (b)' Variable'power'drive' (c)' Constant'torque'drive' (d)' Variable'torque'drive' ' 35.'Two'dc'series'motors'connected'in'series'are'driving'the'same'mechanical'load.'If' the'motors'are'now'connected'in'parallel'the'speed'becomes' (a)' Slightly'less'than'double' (b)' Slightly'less'than'half' (c)' Slightly'more'than'double' (d)' Slightly'more'than'half' ' 36.'The'direction'of'rotation'of'dc'shunt'motor'can'be'reversed'by'interchanging' (a)' The'supply'terminals' (b)' The'field'terminals'only' (c)' The'armature'terminals'only' (d)' Either'field'or'the'armature'terminals' ' 37.'The'field'of'selfYexcited'generator'is'excited'by' (a)' dc' (b)' ac' (c)' Its'own'current' (d)' ac'and'dc'current' ' 38.'The'DC'generator'works'on'the'principle'of' (a)' Faraday’s'laws'if'electronic' (b)' Lenz’s'law' magnetic'induction' (c)' The'current'carrying'conductor' (d)' Induction' places'in'the'magnetic'field'an' '


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e.m.f'is'produced'' ' 39.'Maximum'efficiency'of'the'motor'will'occur'when' (a)' Copper'losses'>'Iron'losses' (b)' Copper'losses'<'Iron'losses' (c)' Copper'losses'='friction'losses' (d)' Copper'losses'='constant'losses' ' 40.'Interpoles'are'connected'in'series'with'the'' (a)' Line' (b)' Armature'winding' (c)' Shunt'field'winding' (d)' Line'and'armature'winding' ' 41.'When'the'field'terminals'and'armature'terminals'are'both'interchanged'of'dc'shunt' motor,'then'the' (a)' Motor'will'not'run' (b)' Motor'will'run'in'the'same'direction' (c)' Motor'will'run'in'opposite' (d)' Speed'of'motor'will'change' direction' ' 42.'Residual'magnetism'is'the'essential'prerequisite'for'starting'which'type'of'd.c' generator?' (a)' Separately'excited'generator' (b)' Shunt'generator' (c)' Series'generator' (d)' All'of'these' ' 43.'The'yoke'of'dc'machine' (a)' is'laminated' (b)' in'not'laminated' (c)' may'or'may'not'be'laminated' (d)' none'of'these' ' ' ' ' 44.'The'presence'of'equalizer'bar' (a)' is'essential'for'parallel'operation' (b)' is'preferable'for'parallel'operation'of' of'compound'generator' compound'generators' (c)' is'unnecessary'for'parallel' (d)' none'of'these' operation'of'compound' generators' ' 45.'The'difference'between'no'load'and'full'load'speeds'of'dc'shunt'motor'is'of'the' order'of'' (a)' 20%' (b)' 1%' (c)' 10%' (d)' 99%' ' '


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46.'Swinburne'test'cannot'be'used'for' (a)' Series'motor' (b)' Shunt'motor' (c)' Compound'motor' (d)' None'of'these' ' 47.'In'a'dc'machine'the'maximum'losses'occur'due'to' (a)' Iron'losses' (b)' Mechanical'losses' (c)' Copper'losses' (d)' None'of'above' ' 48.'The'efficiency'of'a'generator'is'usually'expressed'as' (a)' (input'Y'losses)/input' (b)' Output/input' (c)' Output/(output'+'losses)' (d)' None'of'above' ' 49.'The'rotating'part'of'a'dc'motor'is'known'as' (a)' Pole' (b)' Stator' (c)' Armature' (d)' Carbon'brush' ' Transformers) ! 50.'Transformer'is'used'to'change'the'values'of' (a)' Voltage' (b)' Frequency' (c)' Power' (d)' Power'factor' ' 51.'The'path'of'the'magnetic'flux'in'a'transformer'has' (a)' High'reluctance' (b)' Low'resistance' (c)' High'connectivity' (d)' Low'reluctance' ' 52.'Transformer'works'on' (a)' ac' (b)' dc' (c)' an'and'dc' (d)' pulsating'device' ' 53.'Transformer'works'on'the'principle'of' (a)' SelfYinduction' (b)' Mutual'induction' (c)' Faradays'law'of'electromagnetic' (d)' Self'and'mutual'induction'both' induction' ' 54.'Rating'of'transformer'is'given'in' (a)' kVA' (b)' kVAR' (c)' kW' (d)' Watts' ' ' '


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' 55.'If'a'higher'voltage'is'given'to'the'primary'and'low'voltage'is'taken'from'the' secondary'of'transformer'is'it'called' (a)' StepYup' (b)' StepYdown' (c)' Instrument'transformer' (d)' Stabilizer' ' 56.'The'emf'induced'in'the'secondary'winding'of'a'transformer'depend'upon' (a)' Number'of'turns' (b)' Flux' (c)' Supply'frequency' (d)' All'of'these' ' 57.'Electrical'power'is'transferred'from'one'coil'to'the'other'coil'in'a'transformer' (a)' Electrically' (b)' Electromagnetically' (c)' Magnetically' (d)' Physical' ' 58.'As'compared'to'an'amplifier,'a'transformer'cannot' (a)' Increase'the'output'voltage' (b)' Increase'the'output'current' (c)' Increase'output'power' (d)' None'of'these' ' 59.'Two'transformers'are'operating'in'parallel.'They'will'share'the'load'depending'upon' their' (a)' Efficiency'' (b)' Rating' (c)' Leakage'reactance' (d)' Per'unit'impedance' ' 60.'What'is'the'typical'use'of'an'autoYtransformer?' (a)' Isolating'transformer' (b)' Toy'transformer' (c)' Control'transformer' (d)' Variable'transformer' ' 61.'In'any'transformer,'the'voltage'per'turn'in'primary'and'secondary'remains' (a)' Always'same' (b)' Always'in'ratio'of'K' (c)' Always'different' (d)' Sometimes'same' ' 62.'The'special'silicon'steel'in'used'for'laminations'because' (a)' Eddy'current'losses'are'reduced' (b)' Hysteresis'losses'are'reduced' (c)' Both'losses'are'reduced' (d)' None'of'these' ' 63.'CrossYover'winding'are'used'for' (a)' High'voltage'winding'of'small' (b)' Low'voltage'winding'of'small'rating' rating'transformers' transformers' (c)' High'voltage'winding'of'large' (d)' None'of'these' rating'transformers' ' '


'


' 64.'The'input'power'to'a'threeYphase'transformer'is'given'by' (a)' 3×!/0 &/0 ' (b)' 3×!/0 &/0 1234' (c)' 3×!5 &6 1234' (d)' 3×!/0 &/0 7814' ' 65.'The'leakage'flux'of'a'transformer'is'defined'as'following' (a)' It'is'flux'which'is'linked'with'the' (b)' It'is'the'magnetic'flux'which'is'linked' primary'and'the'secondary' either'only'with'the'primary'or'only' winding' with'the'secondary' (c)' It'is'the'flux'whose'path'is' (d)' None'of'these' exclusively'through'the'air' ' ' ' ' 66.'Iron'loss'in'an'actual'transformer'remains'practically'constant'from'noYload'to'fullY load'because' (a)' Core'flux'remains'practically' (b)' Primary'voltage'remains'voltage' constant' (c)' Value'of'transformation'ration' (d)' Permeability'of'transformer'core' remains'constant' remains'constant' ' 67.'The'primary'reason'why'openYcircuit'test'is'performed'on'the'lowYvoltage'winding' of'the'transformer'is'that'it' (a)' Draws'sufficiently'large'noYload' (b)' Requires'least'voltage'to'perform'the' current'for'convenient'reading' test' (c)' Needs'minimum'power'input' (d)' Has'become'a'universal'custom' ' 68.'NoYload'test'on'a'transformer'is'carried'out'to'determine' (a)' Copper'loss' (b)' FullYload'current' (c)' Magnetizing'current' (d)' Efficiency'of'the'transformer' ' 69.'The'shortYcircuit'test'in'a'transformer'is'used'to'determine' (a)' Iron'loss'at'any'load' (b)' Copper'loss'at'any'load' (c)' Hysteresis'loss' (d)' EddyYcurrent'loss' ' 70.'The'main'reason'for'using'high'voltage'for'longYdistance'power'transmission'is'to' (a)' Provide'industrial'establishments' (b)' Enable'the'national'grid'system'to'be' with'high'voltage' used' (c)' Reduce'time'of'transmission' (d)' Reduce'transmission'losses'due'to' conductor'resistance' '


'


71.'The'ordinary'efficiency'of'a'given'transformer'is'maximum'when' (a)' It'runs'at'half'fullYload' (b)' It'runs'at'fullYload' (c)' Its'copper'loss'equals'iron'loss' (d)' It'runs'overload' ' 72.'The'main'purpose'of'using'core'in'a'transformer'is'to' (a)' Decrease'iron'losses' (b)' Prevent'eddy'current'loss' (c)' Eliminate'magnetic'hysteresis' (d)' Decrease'reluctance'of'the'common' magnetic'flux'path' ' 73.'While'conducting'shortYcircuit'test'on'a'transformer'which'of'the'following'side'is' shortYcircuit' (a)' H.V'side' (b)' L.V'side' (c)' Primary'side' (d)' None'of'these' ' 74.'Spiral'winding'is'suitable'only'for'winding' (a)' Carrying'low'current' (b)' Carrying'very'high'current' (c)' Rated'for'high'voltage' (d)' Rated'for'low'voltage' ' 75.'CrossYover'winding'is'suitable'for' (a)' Low'voltage'winding'of'small' (b)' High'voltage'winding'of'small' transformers' transformers' (c)' Low'voltage'winding'of'large' (d)' High'voltage'winding'of'large' winding' transformers' ' 76.'For'shortYcircuit'and'openYcircuit'test'of'a'transformer'the'instrument'are'connected' on' (a)' Equivalent'resistance'and'leakage' (b)' Equivalent'resistance'and'core'loss' reactance' (c)' Magnetizing'current'and' (d)' Magnetizing'current'and'core'loss' equivalent'leakage'reactance' ' ' 77.'The'leakage'flux'in'a'transformer'depends'upon' (a)' The'applied'voltage' (b)' The'frequency' (c)' The'load'current' (d)' The'mutual'flux' ' 78.'Eddy'current'loss'in'a'transformer'depend'on' (a)' Both'voltage'and'frequency' (b)' Voltage'alone' (c)' Load'current'alone' (d)' Thickness'of'core' ' '


'


79.'In'a'transformer' (a)' Both'o.c'and's.c'tests'are' (b)' o.c'test'is'conducted'on'h.v'side'and' conducted'on'l.v'side' s.c'tests'on'l.v'side' (c)' o.c'test'is'conducted'on'l.v'side' (d)' both'o.c'and's.c'tests'are'conducted' and's.c'tests'on'h.v'side' on'h.v'side' ' 80.'Transformers'zero'voltage'regulation'occurs'at' (a)' Unity'p.f' (b)' Leading'p.f' (c)' Lagging'p.f' (d)' Zero'p.f'leading' ' 81.'The'loss'due'to'eddy'current'in'a'transformer'is'' (a)' Directly'proportional'to'the' (b)' Indirectly'proportional'to'the'current' current' (c)' Indirectly'proportional'to'the' (d)' Directly'proportional'to'the' resistance'of'the'winding' resistance'of'the'winding' ' Alternator)and)Synchronous)Machines) ! 82.'Alternator'Generates' (a)' d.c' (b)' a.c' (c)' dc'and'ac'both' (d)' pulsating'd.c' ' 83.'The'rotor'of'the'alternator'requires' (a)' d.c' (b)' a.c' (c)' pulsating'd.c' (d)' none'of'the'above' ' 84.'The'different'types'of'rotor'of'an'alternator'are' (a)' Salient'pole'type' (b)' Cylindrical'pole'type' (c)' Both'salient'pole'and'cylindrical' (d)' None'of'these' pole'type' ' 85.'Salient'pole'type'rotors'are'generally'used'with'prime'movers'of' (a)' High'speed' (b)' Low'speed' (c)' Medium'speed' (d)' Low'and'high'speed' ' 86.'Cylindrical'pole'type'rotors'are'generally'used'with'prime'movers'of' (a)' High'speed' (b)' Low'speed' (c)' Medium'speed' (d)' Low'and'high'speed' ' 87.'The'frequency'of'emf'generated'depends'upon' '


(a)' Speed'of'the'alternator' (c)' Type'of'alternator'

'


(b)' Number'of'poles'of'the'alternator' (d)' Both'speed'and'number'of'poles'of' the'alternator'

' ' 88.'The'condition'for'running'two'alternators'in'parallel'are' (a)' Terminals'voltage'should'be'same' (b)' Frequency'should'be'same' (c)' Phase'sequence'should'be'same' (d)' All'the'above'three' ' 89.'The'frequency'per'revolution'in'an'alternator'is'equal'to' (a)' Number'of'poles' (b)' Number'of'armature'conductor' (c)' Number'of'pair'of'poles' (d)' None'of'these' ' 90.'The'power'factor'of'the'input'power'to'a'synchronous'motor'is'adjusted'by'varying' (a)' Number'of'poles' (b)' Magnitude'of'excitation' (c)' Magnitude'of'armature'reaction' (d)' None'of'these' ' 91.'The'function'of'damper'winding'in'synchronous'motor'is'to'provide,'starting'torque' and' (a)' to'reduce'speed' (b)' to'prevent'hunting' (c)' to'increase'speed' (d)' none'of'these' ' 92.'In'synchronous'motor,'minimum'armature'current'occurs'at' (a)' Zero'power'factor' (b)' Unity'power'factor' (c)' Lagging'power'factor' (d)' Leading'power'factor' ' 93.'In'a'synchronous'generator' (a)' The'open'circuit'voltage'leads'the' (b)' The'open'circuit'voltage'lags'the' terminal'voltage'by'an'angle' terminal'voltage'by'an'angle'known' known'as'power'angle.' as'power'angle.' (c)' The'open'circuit'voltage'leads'the' (d)' The'open'circuit'voltage'lags'the' terminal'voltage'by'an'angle' terminal'voltage'by'an'angle'known' known'as'overlap'angle' as'overlap'angle.' ' 94.'Armature'reaction'MMF'and'leakage'reactance'of'a'synchronous'machine'are' determined'by' (a)' Open'circuit'test'only' (b)' zero'power'factor'test'only' (c)' open'circuit'and'zero'power' (d)' open'circuit'and'short'circuit'tests' factor'tests' ' '


'


95.'In'3'phase'synchronous'motor' (a)' The'field'MMF'lags'airgap'flux'and' (b)' The'field'MMF'leads'the'airgap'flux' the'airgap'flux'lags'the'armature' and'the'airgap'flux'leads'the' MMF' armature'MMF' (c)' The'field'MMF'leads'the'airgap' (d)' The'field'MMF'lags'the'airgap'and' flux'and'the'airgap'flux'lags'the' the'airgap'flux'leads'the'armature' armature'MMF' MMF' ' 96.'The'synchronous'motor'suns'on' (a)' 3Yphase'a.c'supply' (b)' 3Yphase'ac'and'dc'supply' (c)' dc'supply'only' (d)' 3Yphase'a.c'and'single'phase'a.c'' ' 97.'If'the'field'of'synchronous'motor'is'under'excited,'the'power'factor'will'be' (a)' Power'factor'angle' (b)' Synchronous'angle' (c)' Torque'angle' (d)' Angle'of'retardation' ' 98.'If'the'field'of'synchronous'motor'is'under'excited,'the'power'factor'will'be' (a)' more'than'unity' (b)' unity' (c)' lagging'' (d)' leading' ' ' ' ' ' 99.'The'advantage'of'synchronous'motor'as'compared'to'induction'motor'are'that' (a)' It'runs'at'constant'speed' (b)' It'can'run'over'wide'range'of'power' factors'both'lagging'and'leading' (c)' It’s'torque'is'less'sensitive'to' (d)' All'of'these' change'in'supply'voltage' ' 100.'A'synchronous'motor'working'on'leading'power'factor'and'not'driving'any' mechanical'load'is'known'as' (a)' Synchronous'induction'motor' (b)' Spinning'motor' (c)' Synchronous'condenser' (d)' None'of'the'above' ' 101.'Synchronous'motors'are'usually'operated'at' (a)' Unity'power'factor' (b)' Leading'power'factor' (c)' Lagging'power'factor' (d)' None'of'these' ' 102.'Synchronous'motors'are'used'in' '


(a)' Sizes'greater'than'about'50h.p' (c)' Generally'small'sizes'

'


(b)' All'sizes' (d)' None'of'these'

' 103.'The'shortYcircuit'characteristics'of'an'alternator'is' (a)' Always'linear' (b)' Always'nonYlinear' (c)' Sometimes'linear'and'sometimes' (d)' None'of'these' nonYlinear' ' 104.'High'speed'alternators'usually'have' (a)' Salient'pole'rotors' (b)' Cylindrical'rotors' (c)' Both'salient'pole'and'cylindrical' (d)' None'of'these' rotors' ' 105.'If'the'armature'current'in'in'phase'with'generated'emf,'the'effect'of'armature' reaction'is' (a)' Cross'magnetizing'' (b)' Magnetizing' (c)' Demagnetizing' (d)' None'of'the'above' ' 106.'Electromagnetic'torque'in'rotating'machines'is'present'when'' (a)' Airgap'is'uniform' (b)' Stator'winding'alone'carries'current' (c)' Rotor'winding'alone'carries' (d)' Both'stator'and'rotor'winding'carry' current' current' ' 107.'The'torque'angle'angle'δ'is'defined'as'the'angle'between' (a)' stator'field'axis'and'resultant'field' (b)' rotor'field'axis'and'resultant'field'axis' axis' (c)' stator'field'axis'and'rotor'field' (d)' stator'field'axis'and'mutual'field'exis.' axis' ' 108.'Armature'winding'is'one'in'which'working' (a)' Flux'is'produced'by'field'current' (b)' Flux'is'produced'by'the'working' current'' (c)' emf'is'produced''by'the'working' (d)' emf'is'produced'by'the'leakage'flux' flux' ' 109.'Large'synchronous'machine'are'constructed'with'armature'winding'on'the'stator' because'stationary'armature'winding' (a)' can'be'insulated'satisfactory'for' (b)' can'be'cooled'more'efficiently' higher'voltage' (c)' have'reduced'slip'ring'losses' (d)' all'of'these' '


'

' ' ' ' 110.'In'a'rotating'machine,'the'generated'e.m.f' (a)' is'in'phase'with'working'flux'ϕ'' (b)' (c)' lags'flux'ϕ'by'90°' (d)' ' Induction!motors! 111.'For'induction'motors,'normally' (a)' the'rotor'winding'is'connected'to' (b)' supply'and'the'stator'winding'is' shortYcircuited' (c)' both'the'stator'and'the'rotor' (d)' winding'are'connected'to'supply'


leads'flux'ϕ'by'90°'' lags'flux'ϕ'by'180°'

the'stator'winding'is'connected'to' supply'and'the'rotor'winding'is'short' circuited' the'stator'winding'is'connected'to' supply'and'the'rotor'winding'is'openY circuited'

' 112.'An'induction'motor,'is'general,'is'analogous'to' (a)' An'autoYtransformer' (b)' A'twoYwinding'transformer'with'its' secondary'openYcircuited' (c)' A'twoYwinding'transformer'with' (d)' a'threeYwinding'transformer' its'secondary'shortYcircuited' ' 113.'The'rotor'of'a'3Yphase'induction'rotates'in'the'same'direction'as'the'direction'of' revolving'field'because'of' (a)' Faraday’s'laws'of'electro' (b)' Lenz’s'law' magnetic'induction' (c)' Fleming’s'right'hand'rule' (d)' None'of'these' ' 114.'The'rotor'of'a'3Yphase'induction'motor'always'runs'at' (a)' Synchronous'speed' (b)' Less'than'synchronous'speed' (c)' More'than'synchronous'speed' (d)' None'of'these' ' 115.'The'speed'of'an'induction'motor'is' (a)' Always'less'than'the'synchronous' (b)' Can'be'equal'to'or'less'than'the' speed' synchronous' (c)' Always'more'than'the' (d)' None'of'these' synchronous'speed' ' 116.'Which'of'the'following'statements'about'the'three'phase'induction'motor'is'true?' '


'


(a)' The'speed'of'the'induction'motor' (b)' The'induction'motor'requires'more' cannot'be'controlled'as'easily'and' maintenance'than'a'D.C'motor' efficiently'as'that'of'a'D.C'shunt' motor' (c)' The'price'of'an'induction'motor'is' (d)' The'induction'motor'is'much'more' much'higher'than'that'of'a'D.C' sensitive'to'overloads'than'a'D.C' motor'of'the'same'power'and' motor' speed' ' 117.'Which'of'the'following'formula'is'used'to'calculate'the'synchronous'speed'of'an' induction'motor?' 60×: (a)' 39 = :×;' (b)' 39 = ' ; 60×; ;×: (c)' (d)' 39 = ' 39 = ' : 60 ' 118.'Synchronous'speed'is'defined'as' (a)' The'speed'of'the'rotor'of'an' (b)' The'speed'of'a'synchronous'motor' induction'motor' (c)' The'speed'of'an'induction'motor' (d)' The'natural'speed'at'which'a' at'noYload' magnetic'field'rotates' ' ' ! !

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'


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Electronic Devices Contents 1 Energy Bands

2

2 Intrinsic Semiconductors

3

3 Extrinsic Semiconductors

3

4 Diode

4

5 Current-voltage characteristic

5

6 Types of semiconductor diode

6

7 JFET: junction field effect transistor

9

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8 MOS capacitor

10

9 LASER

10

10 Zener diode

11

11 Bipolar junction transistor

12

12 PIN Diode

13

13 Avalanche Photo Diode

13

14 Semiconductor device fabrication

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1

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1

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Energy Bands • The materials can be classified on the basis of energy gap between their valence band and conduction band. • The valence band is the band consisting of free valence electron and the conduction band is empty band. Conduction takes place when an electron jumps from valence band to conduction band and the gap between these two bands is energy gap. Wider the gap between the bands, higher the energy it requires to shift the electron to conduction band. • In case of conductors, this energy gap is absent or in other words conduction band and valence band overlap each other. Thus electron requires minimum energy to jump from valence band, e.g. Silver, Copper and Aluminium. In insulators, this gap is very large. Therefore, it requires large amount of energy to shift an electron from valence to conduction band. Thus insulators are poor conductors of electricity, e.g. mica, diamond. • Semiconductors have energy gap in between conductors and insulators ( 1 eV) and thus require energy more than conductors but less than insulators. They don’t conduct electricity at low temperature but as temperature increases conductivity increases e.g. silicon and germanium. This is the most basic theory of semiconductor. The materials that are neither conductor nor insulator with energy gap of about 1 eV (electron volt) are called semiconductors. Most common type of materials that are used as semiconductors are germanium (Ge) and silicon (Si) because of their property to withstand high temperature. For Si and Ge energy gap is given as, Eg = 1.213.6 ◊ 10≠4 T eV (for Si)

Eg = 0.785 ≠ 2.23 ◊ 10≠4 T eV (for Ge)

Where, T = absolute temperature in oK Assuming room temperature to be 300 oK, Eg = 0.72eV for Ge and 1.1eV for Si.

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• At room temperature resistivity of semiconductor is in between insulators and conductors. Semiconductors show negative temperature coefficient of resistivity i.e. its resistance decreases with increase in temperature. Both Si and Ge are elements of IV group i.e. both elements have 4 valence electrons. Both form covalent bond with neighbouring atom. At absolute zero temperature both behave as insulator i.e. the valence band is full while conduction band is empty but as temperature is raised more and more covalent bonds break and electrons are set free and jump to conduction band.


Electronic Devices

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Intrinsic Semiconductors

As per theory of semiconductor, semiconductor in its pure form is called as intrinsic semiconductor. In pure semiconductor number of electrons (n) is equal to number of holes (p) and thus conductivity is very low as valence electrons are covalent bonded.

Intrinsic Silicon • A pure semi conductors material which has impurity is do pent atom and no lattice defects is known as intrinsic silicon. The electrical conductivity of this type of silicon is entirely dependent on thermally generated carrier • Silicon is a very important element semiconductor. Silicon is a group IV material. In its outer orbit it has four valance electrons which are held by covalent bonds with the valance electrons of four nearest silicon atom. These valance electrons are not available for electricity. So, at OK intrinsic semi conductor behaves like an insulator. When temperature rises some valance electrons break covalent bonds thermal energy. This vacancy in the band caused by a free electron creates a hole. The electrons gain sufficient energy to jump to conduction band from valance band and leave a hole in the valance band. This energy is equal to 1.2 ev in room temperature (at 300K) which is equal to the band gap energy. • In the intrinsic silicon crystal, the no of holes is equal to the no. of free electrons. New electrons whole pairs are generated by gaining thermal energy but at the same time some are lost due to recombination. • In equilibrium condition, the electron concentration and the hole concentration p are equal and they are equal to the intrinsic carrier concentration of silicon nickel i.e, n = p = ni. The atomic structure is shown below.

3

shop.ssb cra ck.com Extrinsic Semiconductors

As per theory of semiconductor, impure semiconductors are called extrinsic semiconductors. Extrinsic semiconductor is formed by adding a small amount of impurity. Depending on the type of impurity added we have two types of semiconductors: N-type and P-type semiconductors. In 100 million parts of semiconductor one part of impurity is added.

Extrinsic Silicon • A pure semiconductor material having impurity in its crystal is known as extrinsic silicon. Intrinsic semiconductor can be turned in to extrinsic semiconductor when it is doped with controlled amount of dopants. It is doped with donor atom (group V elements) it becomes n-type semiconductor. And it is doped with acceptor atoms (group III elements) it becomes p-type semiconductor. • Let a small amount of group V element is added to an intrinsic semiconductor crystal. The examples of group V elements are p, as sb, etc. They have 5 valance electrons. When they displace a Si atom, the 4 valance electrons made co-valance bonds with neighboring atoms leaving some free electron. The energy necessary for silicon this purpose is about 0.05 ev. This kind of impurity is named as donor. The silicon known as n- type semiconductors as the electrons are negative charged particles. • The Fermi energy level moves closer to the conduction band in the n-type semiconductors. Here the no. of free electrons is increased over intrinsic concentration of electrons and no. of holes is decreased over intrinsic hole concentration. Electrons are majority charge carriers. • If a small amount of group III elements is added to a intrinsic semiconductor crystal, then they displace a silicon atom, group III elements like AI,B, IN have three valance electrons. These three electrons make covalent band with neighboring atoms creating a hole. These kinds of impurity atoms known as acceptors. The semiconductor in known as p-type semiconductor as the hole is assumed to be positively charged.


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N-type Semiconductor In this type of semiconductor majority carriers are electrons and minority carriers are holes. N-type semiconductor is formed by adding pentavalent ( five valence electrons) impurity in pure semiconductor crystal, e.g. P. As, Sb. Four of the five valence electron of pentavalent impurity forms covalent bond with Si atom and the remaining electron is free to move anywhere within the crystal. Pentavalent impurity donates electron to Si that’s why N- type impurity atoms are known as donor atoms. This enhances the conductivity of pure Si. Majority carriers are electrons therefore conductivitry is due to these electrons only and is given by, ‡ = neµe

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P-type Semiconductors

In this type of semiconductor majority carriers are holes and minority carriers are electrons. Ptype semiconductor is formed by adding trivalent ( three valence electrons) impurity in pure semiconductor crystal, e.g. B, Al Ba. Three of the four valence electron of tetravalent impurity forms covalent bond with Si atom. This leaves an empty space which is referred to as hole. When temperature is raised electron from another covalent bond jumps to fill this empty space. This leaves a hole behind. In this way conduction takes place. P- type impurity accepts electron and is called acceptor atom. Majority carriers are holes and therefore conductivity is due to these holes only and is given by, ‡ = neµh

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Diode

A diode is a simple electrical device that allows the flow of current only in one direction. So it can be said to act somewhat like a switch. It is derived from ”di-ode ” which means a device having two electrodes.

The p-n junction is a basic building block in any semiconductor device. It is formed by joining a p type (intrinsic semiconductor doped with a trivalent impurity) and n type semiconductor (intrinsic semiconductor


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doped with a pentavalent impurity) together with a special fabrication technique such that a p-n junction is formed. Hence it is a device with two elements, the p-type forms anode and the n-type forms the cathode. These terminals are brought out to make the external connections.

p-n junction diode A p-n junction diode is made of a crystal of semiconductor, usually silicon, but germanium and gallium arsenide are also used. Impurities are added to it to create a region on one side that contains negative charge carriers (electrons), called n-type semiconductor, and a region on the other side that contains positive charge carriers (holes), called p-type semiconductor. When two materials i.e. n-type and p-type are attached together, a momentary flow of electrons occur from n to p side resulting in a third region where no charge carriers are present. This region is called the depletion region due to the absence of charge carriers (electrons and holes in this case). The diode’s terminals are attached to the n-type and p-type regions. The boundary between these two regions, called a p-n junction, is where the action of the diode takes place. The crystal allows electrons to flow from the N-type side (called the cathode) to the P-type side (called the anode), but not in the opposite direction.

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Current-voltage characteristic

shop.ssb cra ck.com A diode’s I-V characteristic can be approximated by four regions of operation: 1. At very large reverse bias, beyond the peak inverse voltage or PIV, a process called reverse breakdown occurs that causes a large increase in current (i.e., a large number of electrons and holes are created at, and move away from the p-n junction) that usually damages the device permanently. The avalanche diode is deliberately designed for use in the avalanche region. In the Zener diode, the concept of PIV is not applicable. A Zener diode contains a heavily doped pâ n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is ”clamped” to a known value (called the Zener voltage), and avalanche does not occur. Both devices, however, do have a limit to the maximum current and power in the clamped reverse-voltage region. Also, following the end of forward conduction in any diode, there is reverse current for a short time. The device does not attain its full blocking capability until the reverse current ceases. 2. At reverse biases more positive than the PIV, has only a very small reverse saturation current. In the reverse bias region for a normal P-N rectifier diode, the current through the device is very low (in the µA range). However, this is temperature dependent, and at sufficiently high temperatures, a substantial amount of reverse current can be observed (mA or more). 3. With a small forward bias, where only a small forward current is conducted, the current-voltage curve is exponential in accordance with the ideal diode equation. There is a definite forward voltage at which Engineering Knowledge Test

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the diode starts to conduct significantly. This is called the knee voltage or cut-in voltage and is equal to the barrier potential of the p-n junction. This is a feature of the exponential curve, and is seen more prominently on a current scale more compressed than in the diagram here. 4. At larger forward currents the current-voltage curve starts to be dominated by the ohmic resistance of the bulk semiconductor. The curve is no longer exponential, it is asymptotic to a straight line whose slope is the bulk resistance. This region is particularly important for power diodes. The effect can be modelled as an ideal diode in series with a fixed resistor.

Forward Biased When the diode is forward biased, due to the negative terminal on the n-side, electrons from the n-side are pushed towards the p-region. Similarly due to positive voltage on the p-side of the diode, Holes from the p-region are pushed towards n-side. Due to this the electrons will start converting the positive ions in the p-region into neutral atoms and holes will start converting the negative ions in the n-region to neutral atoms. Hence width of the depletion region starts reducing due to reduction in the barrier potential. (As the atoms in the depletion region are getting converted into neutral atoms less and less charged ions remain in this region with increase in supply voltage, hence width decreases.) This keeps happening and at a certain point the depletion region collapses and there is no opposition to the flow of current. Hence large number of electrons and holes will cross the junction and make the current to flow from anode to cathode. Hence, forward biased electrical resistance of diode is very small and hence there is a small voltage drop (Practical condition, ideally there should be 0 forward resistance) across it. Its value for silicon diode is about 0.7 V.

Reverse Biased When the diode is reverse biased the hole from the p-side will get attracted towards the negative terminal of the supply and electrons from the n-side are attracted towards the positive terminal. Hence the process of widening of the depletion region takes place and hence more and more opposition to the flow of current takes place. Hence, ideally the reverse biased resistance of the diode is infinite and no current flows from the diode when it is reversed biased. Due to large reverse biased voltage, suddenly large current will flow through the reverse biased voltage. Due to this large power gets dissipated in the diode which may damage it permanently.

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Types of semiconductor diode

There are several types of pâ n junction diodes, which emphasize either a different physical aspect of a diode often by geometric scaling, doping level, choosing the right electrodes, are just an application of a diode in a special circuit, or are really different devices like the Gunn and laser diode and the MOSFET:

Avalanche diodes These are diodes that conduct in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. These are electrically very similar to Zener diodes (and are often mistakenly called Zener diodes), but break down by a different mechanism: the avalanche effect. This occurs when the reverse electric field across the p-n junction causes a wave of ionization, reminiscent of an avalanche, leading to a large current. Avalanche diodes are designed to break down at a well-defined reverse voltage without being destroyed. The difference between the avalanche diode (which has a reverse breakdown above about 6.2 V) and the Zener is that the channel length of the former exceeds the mean free path of the electrons, so there are collisions between them on the way out. The only practical difference is that the two types have temperature coefficients of opposite polarities.

Cat’s whisker or crystal diodes These are a type of point-contact diode. The cat’s whisker diode consists of a thin or sharpened metal wire pressed against a semiconducting crystal, typically galena or a piece of coal. The wire forms the anode and the crystal forms the cathode. Cat’s whisker diodes were also called crystal diodes and found application


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in crystal radio receivers. Cat’s whisker diodes are generally obsolete, but may be available from a few manufacturers.

Constant current diodes These are actually JFETs with the gate shorted to the source, and function like a two-terminal currentlimiting analog to the voltage-limiting Zener diode. They allow a current through them to rise to a certain value, and then level off at a specific value. Also called CLDs, constant-current diodes, diode-connected transistors, or current-regulating diodes.

Esaki or tunnel diodes These have a region of operation showing negative resistance caused by quantum tunneling, allowing amplification of signals and very simple bistable circuits. Due to the high carrier concentration, tunnel diodes are very fast, may be used at low (mK) temperatures, high magnetic fields, and in high radiation environments. Because of these properties, they are often used in spacecraft.

Gunn diodes These are similar to tunnel diodes in that they are made of materials such as GaAs or InP that exhibit a region of negative differential resistance. With appropriate biasing, dipole domains form and travel across the diode, allowing high frequency microwave oscillators to be built.

Light-emitting diodes (LEDs) In a diode formed from a direct band-gap semiconductor, such as gallium arsenide, carriers that cross the junction emit photons when they recombine with the majority carrier on the other side. Depending on the material, wavelengths (or colors) from the infrared to the near ultraviolet may be produced. The forward potential of these diodes depends on the wavelength of the emitted photons: 2.1 V corresponds to red, 4.0 V to violet. The first LEDs were red and yellow, and higher-frequency diodes have been developed over time. All LEDs produce incoherent, narrow-spectrum light; ”white” LEDs are actually combinations of three LEDs of a different color, or a blue LED with a yellow scintillator coating. LEDs can also be used as low-efficiency photodiodes in signal applications. An LED may be paired with a photodiode or phototransistor in the same package, to form an opto-isolator.

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Laser diodes When an LED-like structure is contained in a resonant cavity formed by polishing the parallel end faces, a laser can be formed. Laser diodes are commonly used in optical storage devices and for high speed optical communication.

Thermal diodes This term is used both for conventional p-n diodes used to monitor temperature due to their varying forward voltage with temperature, and for Peltier heat pumps for thermoelectric heating and cooling. Peltier heat pumps may be made from semiconductor, though they do not have any rectifying junctions, they use the differing behaviour of charge carriers in N and P type semiconductor to move heat.

Photodiodes All semiconductors are subject to optical charge carrier generation. This is typically an undesired effect, so most semiconductors are packaged in light blocking material. Photodiodes are intended to sense light(photodetector), so they are packaged in materials that allow light to pass, and are usually PIN (the kind of diode most sensitive to light). A photodiode can be used in solar cells, in photometry, or in optical communications. Multiple photodiodes may be packaged in a single device, either as a linear array or as a two-dimensional array. These arrays should not be confused with charge-coupled devices.


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PIN diodes A PIN diode has a central un-doped, or intrinsic, layer, forming a p-type/intrinsic/n-type structure. They are used as radio frequency switches and attenuators. They are also used as large-volume, ionizing-radiation detectors and as photodetectors. PIN diodes are also used in power electronics, as their central layer can withstand high voltages. Furthermore, the PIN structure can be found in many power semiconductor devices, such as IGBTs, power MOSFETs, and thyristors.

Schottky diodes Schottky diodes are constructed from a metal to semiconductor contact. They have a lower forward voltage drop than p-n junction diodes. Their forward voltage drop at forward currents of about 1 mA is in the range 0.15 V to 0.45 V, which makes them useful in voltage clamping applications and prevention of transistor saturation. They can also be used as low loss rectifiers, although their reverse leakage current is in general higher than that of other diodes. Schottky diodes are majority carrier devices and so do not suffer from minority carrier storage problems that slow down many other diodes-so they have a faster reverse recovery than p-n junction diodes. They also tend to have much lower junction capacitance than p-n diodes, which provides for high switching speeds and their use in high-speed circuitry and RF devices such as switched-mode power supply, mixers, and detectors.

Super barrier diodes Super barrier diodes are rectifier diodes that incorporate the low forward voltage drop of the Schottky diode with the surge-handling capability and low reverse leakage current of a normal p-n junction diode.

Gold-doped diodes

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As a dopant, gold (or platinum) acts as recombination centers, which helps a fast recombination of minority carriers. This allows the diode to operate at signal frequencies, at the expense of a higher forward voltage drop. Gold-doped diodes are faster than other p-n diodes (but not as fast as Schottky diodes). They also have less reverse-current leakage than Schottky diodes (but not as good as other p-n diodes). A typical example is the 1N914.

Snap-off or Step recovery diodes The term step recovery relates to the form of the reverse recovery characteristic of these devices. After a forward current has been passing in an SRD and the current is interrupted or reversed, the reverse conduction will cease very abruptly (as in a step waveform). SRDs can, therefore, provide very fast voltage transitions by the very sudden disappearance of the charge carriers.

Stabistors or Forward Reference Diodes The term stabistor refers to a special type of diodes featuring extremely stable forward voltage characteristics. These devices are specially designed for low-voltage stabilization applications requiring a guaranteed voltage over a wide current range and highly stable over temperature.

Transient voltage suppression diode (TVS) These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltage transients.Their p-n junctions have a much larger cross-sectional area than those of a normal diode, allowing them to conduct large currents to ground without sustaining damage.

Varicap or varactor diodes These are used as voltage-controlled capacitors. These are important in PLL (phase-locked loop) and FLL (frequency-locked loop) circuits, allowing tuning circuits, such as those in television receivers, to lock quickly. They also enabled tunable oscillators in early discrete tuning of radios, where a cheap and stable, but fixedfrequency, crystal oscillator provided the reference frequency for a voltage-controlled oscillator.


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Zener diodes These can be made to conduct in reverse bias (backward), and are correctly termed reverse breakdown diodes. This effect, called Zener breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference. The term Zener diode is colloquially applied to several types of breakdown diodes, but strictly speaking Zener diodes have a breakdown voltage of below 5 volts, whilst those above that value are usually avalanche diodes. In practical voltage reference circuits, Zener and switching diodes are connected in series and opposite directions to balance the temperature coefficient to near-zero. Some devices labeled as high-voltage Zener diodes are actually avalanche diodes (see above). Two (equivalent) Zeners in series and in reverse order, in the same package, constitute a transient absorber (or Transorb, a registered trademark). The Zener diode is named for Dr. Clarence Melvin Zener of Carnegie Mellon University, inventor of the device.

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JFET: junction field effect transistor

JFET is a voltage controlled semiconductor device. In this, the current is carried by only one type of carriers. So, it is a unipolar device. It has a very high input electrical resistance. • JFET consists of a doped Si or GaAs bar. There are ohmic contacts, the two ends of the bar and semiconductor junction on its two sides. If the semiconductor bar is n-type, the two sides of the bar is heavily doped with p - type impurities and this is known as n-channel JFET. On the other hand if the semiconductor bar is p- type, the two sides of the bar is heavily doped with n- type impurities and this is known as p- channel JFET. When a voltage is applied between the two ends, a current which is carried by the majority carriers of the bar flows along the length of the bar. • There are several terminals in JFET. The terminal through which the majority carrier enter the bar and the terminal through which they leave are known as source (s) and drain (D) respectively. The heavily doped region on the two sides is known as the gate (G).

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• In junction field effect transistor, the junction is a reverse biased. As a result, depletion regions form, which extend to the bar. By changing gate to source voltage, the depletion width can be controlled. So, the effective cross section area decreased with increasing reverse bias. So, the drain current is a function of the gate to the source voltage: Now days JFET is obsolete. Its applicants are limited to circuit design. Where it can be used an amplifier and as a switch both.

Applications of JFET 1. Low noise and high input impedance amplifier:Noise is an undesirable disturbance which interferes with the signals information-greater the noise less the information. Energy electronics device cause some amount of noise. If FET s is used at the front end, we get less amount of amplified noise at the output. Now, it has very high input impedance. So, it can be used in high input impedance amplifier. 2. Buffer amplifier:Buffer amplifier should have very high input impedance and low output impedance. Because of high i / p impedance and low output impedance, FET acts as great buffer amplifier. the common drain mode can be used in this purpose. 3. R.F. Amplifier:JFET is good in low current signal operation as it is a voltage controlled semiconductors device. It has very low noise level. So, it can be used as RF amplifier in receiver sections of communication field. 4. Current source:Here all the supply voltage appears across load. If the current tries to increase very much, the excessive load a current drives the JFET in to active region. Thus JFET acts as a current source . 5. Multiplexer:Analog multiplexer circuit can be made using JFETs. An example is given below.


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MOS capacitor

An MOS[Metal oxide semiconductor]. capacitor is made of a semiconductor body or substrate, an insulator and a metal electrode called a gate. Practically the metal is a heavily doped n+ poly-silicon layer which behaves as a metal layer. The dielectric material used between the capacitor plates is silicon dioxide (SiO2 ). The metal acts as one plate of the capacitor and the semiconductor layer which may be n-type or p-type acts as another plate.

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The capacitance of the MOS capacitor depends upon the voltage applied on the gate terminal. Usually the body is grounded when the gate voltage is applied. The flat band voltage is an important term related to the MOS capacitor. It is defined as the voltage at which there is no charge on the capacitor plates and hence there is no static electric field across the oxide. An applied positive gate voltage larger than the flat band voltage (VGB>VFB) then positive charge is induced on the metal (poly silicon) gate and negative charge in the semiconductor. The only negative charged electrons are available as negative charges and they accumulate at the surface. This is known as surface accumulation.

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LASER

The acronym LASER stands for Light amplification by stimulated emission of radiation. • A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term ”laser” originated as an acronym for ”light amplification by stimulated emission of radiation”. • A laser differs from other sources of light because it emits light coherently. Spatial coherence allows a laser to be focused to a tight spot, enabling applications like laser cutting and lithography. • Spatial coherence also allows a laser beam to stay narrow over long distances (collimation), enabling applications such as laser pointers. • Lasers can also have high temporal coherence which allows them to have a very narrow spectrum, i.e., they only emit a single color of light. Temporal coherence can be used to produce pulses of light-as short as a femtosecond. Military Laser experiment in the following picture


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Lasers have many important applications. 1. They are used in common consumer devices such as optical disk drives, laser printers, and barcode scanners.

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2. Lasers are used for both fiber-optic and free-space optical communication.

3. They are used in medicine for laser surgery and various skin treatments, and in industry for cutting and welding materials. 4. They are used in military and law enforcement devices for marking targets and measuring range and speed. 5. Laser lighting displays use laser light as an entertainment medium.

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Zener diode

A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but also permits it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, ”Zener knee voltage”, ”Zener voltage”, ”avalanche point”, or ”peak inverse voltage”.

Zener effect The Zener effect is a type of electrical breakdown in a reverse biased p-n diode in which the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor, leading to a large number of free minority carriers, which suddenly increase the reverse current. Zener breakdown is employed in a Zener diode. Engineering Knowledge Test

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Mechanism Under a high reverse-bias voltage, the p-n junction’s depletion region expands, leading to a high strength electric field across the junction. A sufficiently strong electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor leading to a large number of free charge carriers. This sudden generation of carriers rapidly increases the reverse current and gives rise to the high slope conductance of the Zener diode.

shop.ssb cra ck.com Zener Application • Waveform clipper

Two Zener diodes facing each other in series will act to clip both halves of an input signal. Waveform clippers can be used to not only reshape a signal, but also to prevent voltage spikes from affecting circuits that are connected to the power supply.

• Voltage shifter

A Zener diode can be applied to a circuit with a resistor to act as a voltage shifter. This circuit lowers the input voltage by a quantity that is equal to the Zener diode’s breakdown voltage.

• Voltage regulator

A Zener diode can be applied to a circuit to regulate the voltage applied to a load, such as in a linear regulator.

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Bipolar junction transistor

• A bipolar junction transistor is a three terminal semiconductor device consisting of two p-n junctions which is able to amplify or ”magnify” a signal. It is a current controlled device. The three terminals of the BJT are the base, the collector and the emitter. A signal of small amplitude if applied to the base is available in the amplified form at the collector of the transistor. This is the amplification


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provided by the BJT. Note that it does require an external source of DC power supply to carry out the amplification process. • Bipolar transistors are so named because their operation involves both electrons and holes. These two kinds of charge carriers are characteristic of the two kinds of doped semiconductor material; electrons are majority charge carriers in n-type semiconductors, whereas holes are majority charge carriers in p-type semiconductors. In contrast, unipolar transistors such as the field-effect transistors have only one kind of charge carrier. • Charge flow in a BJT is due to diffusion of charge carriers across a junction between two regions of different charge concentrations. The regions of a BJT are called emitter, collector, and base.[note 1] A discrete transistor has three leads for connection to these regions. Typically, the emitter region is heavily doped compared to the other two layers, whereas the majority charge carrier concentrations in base and collector layers are about the same. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where there are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices. The three parts of a BJT are collector, emitter and base. Modes of operation for BJT transistor. The modes are i) Common Base (CB) mode ii) Common Emitter (CE) mode iii) Common Collector (CC) mode

Application of BJT • BJT’s are used in discrete circuit designed due to availability of many types, and obviously because of its high transconductane and output resistance which is better than MOSFET.

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• BJT’s are suitable for high frequency application also. That’s why they are used in radio frequency for wireless systems. Another application of BJT can be stated as small signal amplifier, metal proximity photocell, etc. • BJTs can be used as amplifiers, switches, or in oscillators. BJTs can be found either as individual discrete components, or in large numbers as parts of integrated circuits.

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PIN Diode

1. PIN photodiode is a kind of photo detector, it can convert optical signals into electrical signals. 2. This technology was invented in the latest of 1950’s. There are three regions in this type of diode. There is a p-region an intrinsic region and an n-region. The p-region and n-region are comparatively heavily doped than the p-region and n-region of usual p-n diodes. The width of the intrinsic region should be larger than the space charge width of a normal p-n junction. The PIN photodiode operates with an applied reverse bias voltage and when the reverse bias is applied, the space charge region must cover the intrinsic region completely. Electron hole pairs are generated in the space charge region by photon absorption. 3. The switching speed of frequency response of photodiode is inversely proportional to the life time. The switching speed can be enhanced by a small minority carrier lifetime. For the photo detector applications where the speed of response is important, the depletion region width should be made as large as possible for small minority carrier lifetime as a result the switch speed also increases. This can be achieved PIN photodiode as the insertion of intrinsic region the space charge width larger. The diagram of a normal PIN photodiode is given below.

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Avalanche Photo Diode

• Avalanche photo diode is a kind of photo detector which can convert signals into electrical signals pioneering research work in the development of avalanche diode was done mainly in 1960’s. Engineering Knowledge Test

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• Avalanche photodiode structural configuration is very similar to the PIN photodiode. A PIN photodiode consists of three regionsa) p-region, b) intrinsic region, c) n-region.

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• The difference is that reverse bias applied is very large to cause impact ionization. For silicon as the sc material, a diode will need between 100 to 200 volts. Firstly electron- hole pairs are generated by photon absorption in the depletion region. These generate more electron hole pairs through impact ionization. These are swept out of the depletion region quickly, i.e, the transit time is very less.

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Semiconductor device fabrication

Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photo lithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications.

Wafers A typical wafer is made out of extremely pure silicon that is grown into mono-crystalline cylindrical ingots (boules) up to 300 mm (slightly less than 12 inches) in diameter using the Czochralski process. These ingots are then sliced into wafers about 0.75 mm thick and polished to obtain a very regular and flat surface.

Thermal oxidation In microfabrication, thermal oxidation is a way to produce a thin layer of oxide (usually silicon dioxide) on the surface of a wafer. The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it. The rate of oxide growth is often predicted by the Deal-Grove model. Thermal oxidation may be applied to different materials, but this article will only consider oxidation of silicon substrates to produce silicon dioxide.


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Ion implantation Ion implantation is a materials engineering process by which ions of a material are accelerated in an electrical field and impacted into a solid. This process is used to change the physical, chemical, or electrical properties of the solid. Ion implantation is used in semiconductor device fabrication.

Photolithography Photolithography, also termed optical lithography or UV lithography, is a process used in microfabrication to pattern parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical ”photoresist”, or simply ”resist,” on the substrate. A series of chemical treatments then either engraves the exposure pattern into, or enables deposition of a new material in the desired pattern upon, the material underneath the photo resist. For example, in complex integrated circuits, a modern CMOS wafer will go through the photolithographic cycle up to 50 times.

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Electronic Devices


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Electronic'Devices'MCQs'

Electronic*Devices*MCQs* ! 1.''Electronics'is'the'branch'of'engineering'which'deals'with'the'application'of' (a)' electronic'devices' (b)' production'of'electronic'components' (c)' fission'of'uranium'nuclei' (d)' generation'of'small'power' ' 2.''The'color'code'of'a'1k'Ω'resistance'is' (a)' black,'brown,'red' (b)' red,'brown,'brown' (c)' brown,'black,'red' (d)' black,'black,'red' ' 3.''Which'one'of'the'following'has'the'ability'to'act'as'an'open'circuit'for'dc'and'a'short' circuit'for'ac'of'high'frequency.' (a)' an'induction'' (b)' a'capacitor' (c)' a'resistor' (d)' none'of'the'above' ' 4.''A'device'having'characteristics'very'close'to'that'of'an'ideal'voltage'source'is' (a)' Vacuum'diode' (b)' Zener'diode' (c)' Transistor' (d)' FET' ' 5.''The'maximum'number'of'electronics'which'the'valence'shell'of'an'atom'can'have'is' (a)' 6' (b)' 8' (c)' 18' (d)' 2' ' 6.''An'electron'with'velocity'‘u’'is'placed'in'an'electric'filed'E'and'magnetic'field'B.'The' force'experienced'by'the'electron'is'given'by'' (a)' UeE' (b)' Ueu'×'B' (c)' Ue(u×E+B)' (d)' Ue(E+u×B)' ' 7.''The'bonding'forces'in'compound'semiconductors,'such'as'GaAs,'arise'from' (a)' Ionic'bonding' (b)' Metallic'bonding' (c)' Covalent'bonding' (d)' Combination'of'ionic'and'covalent' bonding' ' 8.''Elements'can'reach'a'stable'atomic'structure'by' (a)' Losing'electrons'only' (b)' Gaining'electrons'only' (c)' Losing'and'gaining'or'sharing' (d)' Collisions'between'atoms' electrons' ' 9.''Which'one'of'the'following'materials'does'not'have'a'covalent'bond?' (a)' Metal' (b)' Silicon' '


(c)' Organic'polymers''

'


(d)' diamond'

' 10.'The'covalent'bond'is'formed'by' (a)' transfer'of'electrons'between' (b)' sharing'of'electrons'between'atoms' atoms' (c)' sharing'of'variable'number'of' (d)' removing'the'electron'completely' electronics'by'a'variable'number' ' of'atoms' ' 11.''Conduction'electrons'have'more'mobility'than'holes'because'they' (a)' are'lighter' (b)' experience'collision'less'frequently' (c)' have'negative'charge' (d)' need'less'energy'to'move'them' ' ' ' 12.''Which'of'the'following'statements'if'correct?' (a)' copper'has'partially'filled' (b)' diamond'has'a'completely'filled' conduction'band' conduction'band'but'an'empty' valence'band' (c)' silicon'has'partially'filled' (d)' energy'gap'between'conduction'and' conduction'band'and'an'empty' valence'bands'in'diamond'is'smaller' valence'band' than'in'silicon' ' 13.''An'electron'in'the'conduction'band' (a)' is'raised'to'an'higher'orbit' (b)' jumps'from'one'orbit'to'another' (c)' comes'to'the'ground'state' (d)' is'completely'removed' ' 14.''For'insulators,'the'forbidden'gap'is'of'the'order'of' (a)' 5'eV' (b)' 1'eV' (c)' 0.1'eV' (d)' zero' ' 15.''A'semiconductor'has'a'' (a)' negative'temperature'coefficient' (b)' positive'temperature'coefficient'of' of'resistance' resistance' (c)' constant'temperature'coefficient' (d)' zero'temperature'coefficient'of' of'resistance' resistance' ' 16.''The'resistivity'if'a'semiconductor'is'of'the'order'of' (a)' 10#$ Ω&' (b)' 10#$ '()'100'Ω&' (c)' 10#* '()'10* 'Ω&' (d)' +,)-.'10* 'Ω&' '


'


' 17.''In'an'intrinsic'semiconductor,'the'number'of'electrons'is'equal'to'the'number'of' holes'at'which'temperature?' (a)' 0'K' (b)' 0'°C' (c)' high'temperature' (d)' all'temperatures' ' 18.'In'an'intrinsic'semiconductor' (a)' there'are'no'holes'in'the'material' (b)' the'number'of'holes'is'too'small' (c)' electrons'in'the'material'are' (d)' there'is'no'electrons'in'the'material' neutralized'by'holes' ' 19.'Which'one'of'the'following'statements'is'correct?'If'the'Fermi'level'lies'midway' between'the'conduction'and'valence'bands,'then'the'semiconductor'and'valence'bands,' then'the'semiconductor'is' (a)' Intrinsic' (b)' Extrinsic' (c)' pUtype' (d)' nUtype' ' 20.'With'an'increase'in'temperature,'the'Fermi'level'in'an'intrinsic'semiconductor' (a)' moves'closer'to'the'conduction' (b)' moves'closer'to'the'valence'band' band'edge' edge' (c)' moves'into'the'conduction'band' (d)' remains'at'the'center'of'the' forbidden'gap' ' 21.'In'a'semiconductor,'the'movement'of'holes'is'due'to' (a)' movement'of'electrons'in' (b)' movement'of'holes'in'conduction' conduction'band' band' (c)' movement'of'holes'in'valence' (d)' movement'of'electrons'in'valence' band' band' ' 22.''Major'part'of'the'current'in'an'intrinsic'semiconductor'is'because'of' (a)' valence'band'electron' (b)' conduction'band'electron' (c)' thermally'generated'electrons' (d)' holes'in'the'valence'band' ' ' 23.'On'which'of'the'following'factors'does'the'electrical'conductivity'of'a'semiconductor' depends?' 1.! Carrier'concentration' 2.! Carrier'mobility' 3.! Sign'of'the'carrier' Select'the'correct'answer'using'the'codes'given'below' '


(a)' 1'and'2' (c)' 2'and'3'

'


(b)' 1'and'3' (d)' 1,'2'and'3'

' 24.'The'electricity'conductivity'of'a'semiconductor'increases'with'increase'in' temperature'because' (a)' The'mobility'of'the'carriers' (b)' The'carrier'concentration'increases' increases' (c)' Both'carrier'concentration'and' (d)' Thermal'energy'of'electrons' mobility'increase' increases' ' 25.'P'and'Si'have'valencies'of' (a)' 5'and'4' (b)' 4'and'5' (c)' 3'and'5' (d)' 3'and'4' ' 26.'The'bandgap'of'silicon'at'room'tempreture'is' (a)' 1.3'eV' (b)' 0.7'eV' (c)' 1.1'eV' (d)' 1.4'eV' ' 27.'Which'of'the'following'has'the'greatest'mobility?' (a)' Positive'ion' (b)' Negative'ion' (c)' Electron' (d)' Hole' ' 28.'Mobility'is'defined'as' (a)' Diffusion'velocity'per'unit'field' (b)' Drift'velocity'per'unit'field' (c)' Displacement'per'unit'field' (d)' Number'of'free'electrons/number'of' bound'electrons' ' 29.'Mobility'of'electron'is'highest'in' (a)' Si' (b)' Ge' (c)' GaAs'' (d)' C' ' 30.'nUtype'silicon'is'obtained'by'doping'silicon'with' (a)' Germanium' (b)' Aluminium' (c)' Boron' (d)' Phosphorous' ' 31.'To'obtain'nUtype'semiconductor,'the'impurity'added'to'a'pure'semiconductor'is' (a)' trivalent' (b)' tetravalent' (c)' pentavalent' (d)' none'of'these' ' 32.'NUtype'semiconductors' '


(a)' are'negatively'charged' (c)' are'produced'when'phosphorous' is'added'as'an'impurity'to'silicon'

'


(b)' are'produced'when'indium'is'added' as'an'impurity'to'germanium' (d)' none'of'these' '

' 33.'In'PUtype'semiconductor,'there'are' (a)' No'majority'carriers' (b)' Electrons'as'majority'carriers' (c)' Immobile'positive'ions' (d)' Immobile'negative'ions' ' 34.'In'NUtype'semiconductor,'there'are' (a)' Immobile'positive'ions' (b)' Immobile'negative'ions' (c)' No'majority'carriers' (d)' Holes'are'majority'carriers' ' 35.'Hall'effect'can'be'used'' (a)' to'find'type'of'semiconductor' (b)' to'find'carrier'concentration' (weather'PUtype'or'NUtype)' (c)' to'measure'conductivity'' (d)' all'of'the'above' ' 36.'In'a'PUN'junction,'holes'diffuse'from'PUregion'to'NUregion'because' (a)' the'free'electrons'in'the'NUregion' (b)' there'is'greater'concentration'of' attract'them' holes'in'pUregion'in'comparison'to' that'in'NUregion' (c)' they'are'swept'across'the'junction' (d)' none'of'the'above' by'the'potential'difference' ' ' 37.'Current'flow'in'a'semiconductor'depends'on'the'phenomenon'of' 1.! drift' 2.! diffusion' 3.! recombination'all'of'the'above' (a)' 1,'2'and'3' (b)' 1'and'2'only' (c)' 1'and'3'only' (d)' 2'and'3'only' ' 38.'Increase'in'the'applied'reverse'voltage'to'a'pUn'junction'results'an'increase'in'the'' (a)' depletion'width' (b)' barrier'height' (c)' depletion'width'and'barrier' (d)' junction'temperature' height' ' 39.'When'a'positive'dc'is'applied'to'the'nUside'relative'to'pUside,'a'diode'is'said'to'be' given'a' (a)' Forward'bias' (b)' Reverse'bias' '


(c)' Zero'bias'

'


(d)' Neutral'bias'

' 40.'Reverse'saturation'current'in'a'germanium'diode'is'of'the'order'of' (a)' 1'nano'ampere' (b)' 1'micro'ampere' (c)' 1'mA' (d)' 10'mA' ' 41.'In'forward'region'of'its'characteristics,'a'diode'appears'as' (a)' an'ON'switch' (b)' an'OFF'switch' (c)' a'capacitor' (d)' a'high'resistor' ' 42.'At'cutin'voltage'of'a'diode' (a)' the'potential'barrier'is'overcome' (b)' the'potential'barrier'is'strong'and'the' and'the'current'through'the' current'through'the'junction'is' junction'starts'to'increase'rapidly' blocked' (c)' the'diode'almost'behaves'like'a' (d)' the'diode'almost'behaves'like'an' short' open'circuit' ' 43.'As'the'temperature'is'increased,'the'voltage'across'a'diode'carrying'a'constant' current' (a)' increase' (b)' decreases' (c)' remains'constant' (d)' may'increase'or'decrease'depending' on'the'doping'levels'in'the'junction' 44.'Zener'diode'is'used'as'the'main'component'in'dc'supply'for' (a)' rectification' (b)' voltage'regulation' (c)' filter'action' (d)' both'(a)'and'(b)' ' 45.'Tunnel'diode' (a)' is'a'power'diode' (b)' has'light'doping' (c)' has'heavy'doping' (d)' in'a'reverse'recovery'diode' ' 46.'Consider'the'following'statements:'A'tunnel'diode'is' 1.! made'of'Ge'or'GaAs' 2.! an'abrupt'junction'with'both'sides'heavily'doped' 3.! a'hyper'abrupt'junction'with'both'sides'heavily'doped' which'of'these'statements'are'correct?' (a)' 1'and'2' (b)' 3'and'4' (c)' 1,'3'and'4' (d)' 1,'2'and'4' ' 47.'A'PIN'diode'is'frequently'used'as'a'' (a)' peak'clipper' (b)' voltage'regulator' '


(c)' harmonic'generator'

'


(d)' switching'diode'for'frequency'up'to' GHz'range'

' 48.'A'stepUrecovery'diode' (a)' has'an'extremely'short'recovery' (b)' is'mainly'used'as'a'harmonic' time' generator' (c)' conducts'equally'well'in'both' (d)' is'an'ideal'rectifier'of'high'frequency' directions' signals' ' 49.'Schottky'barrier'diode'can'be'used' (a)' as'switching'power'supplies' (b)' in'communication'receivers'and' operating'at'frequency'of'20'GHz' radar'units' (c)' in'clipping'and'clamping'circuits' (d)' all'of'the'above' ' 50.'Write'the'incorrect'statement.'A'Schottky'diode' (a)' has'no'depletion'layer' (b)' has'metal'semiconductor'junctions' (c)' has'fast'recovery'time' (d)' is'a'bipolar'devices' ' 51.'For'a'SchottkyUbarrier'diode'which'one'of'the'following'points'is'true?' (a)' Speed'of'operation'is'low' (b)' IUV'characteristics'is'exactly'same'as' PUN'diode' (c)' Current'is'by'means'of'minority' (d)' There'is'no'PUN'junction' carriers' ' 52.'A'varactor'diode' (a)' has'variable'capacitance' (b)' utilizes'transition'capacitance'of'a' junction' (c)' has'always'a'uniform'doping' (d)' is'often'used'in'an'automatic' profile' frequency'control'device' 53.'A'Gunn'diode'is'a'negative'resistance'device,'which'is'used'as'a'source'of' microwaves.'What''is'the'number'of'pUn'junctions?' (a)' 1' (b)' 2' (c)' 3' (d)' 0' ' 54.'Thermistors'are'essentially'semiconductors' (a)' well'suited'to'precision' (b)' widely'used'in'the'lower'temperature' measurement'of'temperature' range'of'U100°'C'to'300°C' (c)' which'behave'as'a'resistors'with'a' (d)' all'of'the'above' high' negative' temperature' ' coefficient'of'resistance' '


'


' ' ' ' 55.'For'construction'of'a'fullUwave'rectifier' (a)' atleast'two'diodes'are'needed' (b)' more'than'two'diodes'are'needed' (c)' atleast'four'diodes'are'needed' (d)' ' ' 56.'Bridge'rectifiers'are'preferred'because' (a)' they'require'small'transformer' (b)' they'have'less'peak'inverse'voltage' (c)' they'need'small'transformer'and' (d)' they'have'low'ripple'factor' also'have'less'peak'inverse' voltage' ' 57.'The'bridge'rectifier'is'preferable'to'a'full'wave'rectifier'with'center'tap'connections' because' (a)' it'uses'four'diodes' (b)' its'transformer'has'no'center'tap' (c)' it'needs'much'small'transformer' (d)' both'(b)'and'(c)' for'the'same'output' ' 58.'The'primary'function'of'a'filter'is'to' (a)' minimize'ac'input'variations' (b)' suppress'odd'harmonics'in'the' rectifier'output' (c)' stabilize'dc'level'of'the'output' (d)' remove'ripples'from'the'rectifier' voltage' output' ' 59.'A'bleeder'resistor'in'a'power'supply'filter'performs'which'of'the'following' functions?' 1.! Protects'the'rectifier'diodes'from'high'voltage'transients' 2.! Ensures'discharge'of'capacitor'when'power'supply'is'turnedUoff' 3.! Provide'constant'output'current'from'the'supply'when'the'load'is'variable' 4.! Improves'output'voltage'regulation' Select'the'correct'answer'using'the'codes'given'' (a)' 1,'2and'3' (b)' 2,'3'and'4' (c)' 1'and'3' (d)' 2'and'4' ' 60.''Choke'input'filter'is'a'' (a)' zero'detector' (b)' average'detector' (c)' peak'detector' (d)' RMS'detector' ' '


'


61.'If'capacitor'value'increases'in'a'capacitor'filter,'then'the'ripple'factor' (a)' increase' (b)' becomes'zero' (c)' decreases' (d)' none'of'these' ' 62.'For'a'step'input,'the'output'of'an'integrator'is' (a)' a'pulse' (b)' a'triangular'waveform' (c)' a'spike' (d)' a'ramp' ' 63.'A'clipper'circuit'always' (a)' needs'a'dc'source' (b)' clips'some'part'of'the'input'signal' (c)' clips'upper'portion'of'input'signal' (d)' clips'upper'portion'of'input'signal' ' 64.'Without'a'dc'source,'a'clipper'acts'like'a' (a)' clamper' (b)' chopper' (c)' rectifier' (d)' demodulator' ' 65.'The'primary'function'of'a'clamper'circuit'is'to' (a)' introduce'a'dc'level'into'ac'signal' (b)' suppress'variations'in'signal'voltage' (c)' raise'+ve'half'cycle'of'the'signal' (d)' lower'–ve'half'cycle'of'the'signal' ' ' Answers:*Electronic*Devices*MCQs* ! 1.!!(a)! 2.!(c)! 3.!(b)! 4.!(b)! 5.!(b)! 6.!(d)! 7.!(c)! 8.!(c)! 9.!(a)! 10.!(b)! 11.!(d)! 12.!(a)! 13.!(d)! 14.!(a)! 15.!(a)! 16.!(c)! 17.!(a)! 18.!(c)! 19.!(a)! 20.!(d)! 21.!(d)! 22.!(c)! 23.!(a)! 24.!(b)! 25.!(a)! 26.!(c)! 27.!(c)! 28.!(b)! 29.!(b)! 30.!(d)! 31.!(c)! 32.!(c)! 33.!(d)! 34.!(a)! 35.!(d)! 36.!(b)! 37.!(d)! 38.!(c)! 39.!(b)! 40.!(b)! 41.!(a)! 42.!(a)! 43.!(b)! 44.!(b)! 45.!(c)! 46.!(a)! 47.!(d)! 48.!(b)! 49.!(d)! 50.!(d)! 51.!(d)! 52.!(c)! 53.!(d)! 54.!(d)! 55.!(a)! 56.!(c)! 57.!(d)! 58.!(d)! 59.!(d)! 60.!(b)! 61.!(c)! 62.!(d)! 63.!(b)! 64.!(c)! 65.!(a)! ! '

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!

!

!

!

Control Engineering

Contents 1 Control system definition

2

2 Open Loop system

3

3 Closed-Loop (feedback control) systems

3

4 Block diagram reduction

4

5 Time domain analysis of first and second order systems

5

6 Routh-Hurwitz Criterion 6.0.1 Routh Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9 9

7 Nyquist stability criterion

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8 Bode diagrams 14 8.1 Bode plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9 Root loci

16

10 Lead compensation

20

11 Lag compensation

20

12 lead-lag compensation

20

13 State space model 21 13.1 State-transition matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

1

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1

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Control system definition

A control system consists of subsystems and processes (or plants) assembled for the purpose of obtaining a desired output with desired performance, given a specified input.

For example, consider an elevator. When the fourth-floor button is pressed on the first floor, the elevator rises to the fourth floor with a speed and floor-levelling accuracy designed for passenger comfort. The push of the fourth-floor button is an input that represents our desired output, shown as a step function in Figure. The performance of the elevator can be seen from the elevator response curve in the figure below. Two major measures of performance are apparent: (1) the transient response and (2) the steadystate error.

shop.ssb cra ck.com Advantages of control system • Power amplification • Remote control

• Convenience of input form

• Compensation for disturbances

Feedback control systems The system that maintains a prescribed relationship between the output and the reference input by comparing them and using the difference as a means of control is called a feedback control system. Feedback control systems are not limited to engineering but can be found in various non-engineering fields as well. The human body, for instance, is a highly advanced feedback control system. Both body temperature and blood pressure are kept constant by means of physiological feedback. In fact, feedback performs a vital function: It makes the human body relatively insensitive to external disturbances, thus enabling it to function properly in a changing environment.

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Open Loop system

• Starts with a subsystem called an input transducer, which converts the form of the input to that used by the controller. • Controller drives a process or a plant. The input is sometimes called the reference, while the output can be called the controlled variable. • Signals, such as disturbances, are shown added to the controller and process outputs via summing junctions. • Distinguishing characteristic of an open-loop system is that it cannot compensate for any disturbances that add to the controller’s driving signal

3

Closed-Loop (feedback control) systems

shop.ssb cra ck.com • The input transducer converts the form of the input to the form used by the controller.

• Output transducer, or sensor, measures the output response and converts it into the form used by the controller. • The first summing junction algebraically adds the signal from the input to the signal from the output, which arrives via the feedback path, the return path from the output to the summing junction. • The output signal is subtracted from the input signal. The result is generally called the actuating signal. • In systems where both the input and output transducers have unity gain, the actuating signal’s value is equal to the actual difference between the input and the output. Under this condition, the actuating signal is called the error. • The closed-loop system compensates for disturbances by measuring the output response, feeding that measurement back through a feedback path, and comparing that response to the input at the summing junction. If there is any difference between the two responses, the system drives the plant, via the actuating signal, to make a correction.

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Block diagram reduction

The presence of a closed loop whereby we can start at point A(s) and move through the system in the feed-forward position and return to point A(s) is noted. The term closed loop system is used to denote systems of this type in which there are feedback elements such that we may go through a complete path in the forward direction and return to the starting point. We may combine the forward transfer functions G3 (s) and G4 (s) and redraw the block diagram that represents the transfer function of this system.

shop.ssb cra ck.com Single-Block Representation

Rules for block diagram manipulation: • Combining parallel transfer functions

• Moving a summing junction

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• Moving a take-off point

• Combining cascaded transfer functions

• Reduction of single-loop feedback system

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5

Time domain analysis of first and second order systems

Poles of a Transfer Function The poles of a transfer function are the values of the Laplace transform variable, s, that cause the transfer function to become infinite or any roots of the denominator of the transfer function that are common to roots of the numerator. Zeros of a Transfer Function The zeros of a transfer function are the values of the Laplace transform variable, s, that cause the transfer function to become zero, or any roots of the numerator of the transfer function that are common to roots of the denominator.

First-Order System A first-order system without zeros

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If the input is a unit step, where R(s) = 1s , the Laplace transform of the step response is C(s), where C(s) = R(s)G(s) =

a s(s + a)

Taking the inverse transform, the step response is given by c(t) = cf (t) + cn (t) = 1 ≠ eat where the input pole at the origin generated the forced response cf (t) = 1, and the system pole at -a, generated the natural response cn (t) = ≠eat .

shop.ssb cra ck.com Let us examine the significance of parameter a, the only parameter needed to describe the transient response. When t =

1 a

1

eat = ea◊ a = e1 = 0.37 Therefore, C(t) at t =

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1 a

1

= 1 ≠ ea◊ a = 1 ≠ 0.37 = 0.63

Control Engineering

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Time constant We call 1/a the time constant of the response. The time constant can be described as the time for e at to decay to 37 percent of its initial value. The reciprocal of the time constant has the units (1/seconds), or frequency. Thus, we can call the parameter a the exponential frequency. Since the derivative of ea t is ≠ a when t = 0, a is the initial rate of change of the exponential at t =0. Thus, the time constant can be considered a transient response specification for a first-order system, since it is related to the speed at which the system responds to a step input.

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Rise Time, Tr

Rise time is defined as the time for the waveform to go from 0.1 to 0.9 of its final value. Settling Time, Ts Settling time is defined as the time for the response to reach, and stay within, 2 percent of its final value. Second-order system Compared to the simplicity of a first-order system, a second-order system exhibits a wide range of responses that must be analyzed and described. Whereas varying a first-order system’s parameter simply changes the speed of the response, changes in the parameters of a second-order system can change the form of the response. – General

– Overdamped Poles: Two real at ≠‡1 , ≠‡2 Natural response: Two exponentials with time constants equal to the reciprocal of the pole locations, or

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c(t) = K1 e‡1 t + K2 e‡2 t

– Underdamped Poles: Two complex at ≠‡d ± jÊd Natural response: Damped sinusoid with an exponential envelope whose time constant is equal to the reciprocal of the pole’s real part. The radian frequency of the sinusoid, the damped frequency of oscillation, is equal to the imaginary part of the poles, or c(t) = Ae‡d t cosÊd t ≠ „

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– Undamped Poles: Two imaginary at at ± jÊ1 Natural response: Undamped sinusoid with radian frequency equal to the imaginary part of the poles, or c(t) = AcosÊ1 t ≠ „

– Crtically damped Poles: Two real at ‡1 Natural response: One term is an exponential whose time constant is equal to the reciprocal of the pole location. Another term is the product of time, t, and an exponential with time constant equal to the reciprocal of the pole location, or c(t) = K1 e‡1 t + K2 e‡2 t

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shop.ssbcrack.com Step responses for second order system damping cases

6

Routh-Hurwitz Criterion

Stability is the most important system specification. If a system is unstable, transient response and steady-state errors are moot points. An unstable system cannot be designed for a specific transient response or steady-state error requirement. – A linear, time-invariant system is stable if the natural response approaches zero as time approaches infinity.

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– A linear, time-invariant system is unstable if the natural response grows without bound as time approaches infinity. – A linear, time-invariant system is marginally stable if the natural response neither decays nor grows but remains constant or oscillates as time approaches infinity. Note: – A system is stable if the natural response approaches zero as time approaches infinity. – A system is unstable if the natural response approaches infinity as time approaches infinity. – A system is marginally stable if the natural response neither decays nor grows but remains constant or oscillates Using Routh-Hurwitz criterion method, we can tell how many closed-loop system poles are in the left half-plane, in the right half-plane, and on the jÊ-axis. We can find the number of poles in each section of the s-plane, but we cannot find their coordinates. The method requires two steps: (1) Generate a data table called a Routh table (2) interpret the Routh table to tell how many closed-loop system poles are in the left half-plane, the right half-plane, and on the jÊ-axis. 6.0.1

Routh Table

Look at the equivalent closed-loop transfer function shown in Figure above. Since we are interested in the system poles, we focus our attention on the denominator. Begin by labelling the rows Dec-2014

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with powers of s from the function highest power of the denominator of the closed-loop transfer function to s0 . Next start with the coefficient of the highest power of s in the denominator and list, horizontally in the first row, every other coefficient. In the second row, list horizontally, starting with the next highest power of s, every coefficient that was skipped in the first row.

Each entry is a negative determinant of entries in the previous two rows divided by the entry in the first column directly above the calculated row. The left-hand column of the determinant is always the first column of the previous two rows, and the right-hand column is the elements of the column above and to the right. The table is complete when all of the rows are completed down to s0 .

shop.ssb cra ck.com Note: Routh-Hurwitz criterion declares that the number of roots of the polynomial that are in the right half-plane is equal to the number of sign changes in the first column. Special Cases 1. Zero only in the first column of a row If the first element of a row is zero, division by zero would be required to form the next row. To avoid this phenomenon, an epsilon, Á, is assigned to replace the zero in the first column. The value Á is then allowed to approach zero from either the positive or the negative side, after which the signs of the entries in the first column can be determined. Determine the stability of the closed-loop transfer function via epsilon method 10 s5 + 2s4 + 3s3 + 6s2 + 5s + 3

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2. Entire row is zero Sometimes while making a Routh table, we find that an entire row consists of zeros because there is an even polynomial that is a factor of the original polynomial. Determine the number of right-half-plane poles in the closed-loop transfer function

Start by forming the Routh table for the denominator of above equation. At the second row we multiply through by 1/7 for convenience. We stop at the third row, since the entire row consists of zeros, and use the following procedure.

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First we return to the row immediately above the row of zeros and form an auxiliary polynomial, using the entries in that row as coefficients. The polynomial will start with the power of s in the label column and continue by skipping every other power of s. Thus, the polynomial formed for this example is P (s) = s4 + 62 + 8 Next we differentiate the polynomial with respect to s and obtain dP (s) = 4s3 + 12s ds Finally, we use the coefficients of to replace the row of zeros. Again, for convenience, the third row is multiplied by 1/4 after replacing the zeros. Table shows that all entries in the first column are positive. Hence, there are no rightâ halfplane poles.

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7

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Nyquist stability criterion

The Nyquist stability criterion determines the stability of a closed-loop system from its open-loop frequency response and open-loop poles. Consider the closed-loop system

The closed-loop transfer function is C(s) G(s) = R(s) 1 + G(s)H(s) For stability, all roots of the characteristic equation 1 + G(s)H(s) = 0, must lie in the left-half s plane. The Nyquist stability criterion relates the open-loop frequency response G(jÊ)H(jÊ) to the number of zeros and poles of 1+G(s)H(s) that lie in the right-half s plane.

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The Nyquist stability criterion is based on a theorem from the theory of complex variables. To understand the criterion, we shall first discuss mappings of contours in the complex plane. We shall assume that the open-loop transfer function G(s)H(s) is representable as a ratio of polynomials in s. For a physically realizable system, the degree of the denominator polynomial of the closed-loop transfer function must be greater than or equal to that of the numerator polynomial.This means that the limit of G(s)H(s) as s approaches infinity is zero or a constant for any physically realizable system. characteristic equation of the system shown in Figure above is, F(s) = 1 + G(s)H(s) = 0 We shall show that, for a given continuous closed path in the s plane that does not go through any singular points, there corresponds a closed curve in the F(s) plane. Problem Consider the following open-loop transfer function G(s)H(s) = The characteristic equation is

2 s≠1

F (s) = 1 + G(s)H(s) = 1 +

2 s+1 = =0 s≠1 s≠1

Conformal mapping of the s-plane grids into the F(s) plane, where F (s) =

Dec-2014

s+1 =0 s≠1

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The function F(s) is analytic everywhere in the s plane except at its singular points. For each point of analyticity in the s plane, there corresponds a point in the F(s) plane. For example, if s=2+j1, then F(s) becomes F (2 + j1) =

2 + j1 + 1 = 2 ≠ j1 2 + j1 ≠ 1

Thus, point s=2+j1 in the s plane maps into point 2-j1 in the F(s) plane. Mapping Theorem Let F(s) be a ratio of two polynomials in s. Let P be the number of poles and Z be the number of zeros of F(s) that lie inside some closed contour in the s plane, with multiplicity of poles and zeros accounted for. Let the contour be such that it does not pass through any poles or zeros of F(s).This closed contour in the s plane is then mapped into the F(s) plane as a closed curve. The total number N of clockwise encirclements of the origin of the F(s) plane, as a representative point s traces out the entire contour in the clockwise direction, is equal to Z-P.

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Nyquist Stability Criterion – This criterion can be expressed as Z = N + P where Z = number of zeros of 1+G(s)H(s) in the right-half s plane N = number of clockwise encirclements of the -1+j0 point P = number of poles of G(s)H(s) in the right-half s plane If P is not zero, for a stable control system, we must have Z=0, or N=-P, which means that we must have P counterclockwise encirclements of the -1+j0 point. If G(s)H(s) does not have any poles in the right-half s plane, then Z=N. Thus, for stability there must be no encirclement of the -1+j0 point by the G(jÊ)H(jÊ) locus. In this case it is not necessary to consider the locus for the entire jÊ axis, only for the positive-frequency portion. The stability of such a system can be determined by seeing if the -1+j0 point is enclosed by the Nyquist plot of G(jÊ)H(jÊ). – We must be careful when testing the stability of multiple-loop systems since they may include poles in the right-half s plane. (Note that although an inner loop may be unstable, the entire closed-loop system can be made stable by proper design.) Simple inspection of encirclements of the -1+j0 point by the G(jÊ)H(jÊ) locus is not sufficient to detect instability in multiple-loop systems. In such cases, however, whether any pole of 1+G(s)H(s) is in the right-half s plane can be determined easily by applying the Routh stability criterion to the denominator of G(s)H(s). – If the locus of G(jÊ)H(jÊ) passes through the -1+j0 point, then zeros of the characteristic equation, or closed-loop poles, are located on the jÊ axis. This is not desirable for practical control systems. For a well-designed closed-loop system, none of the roots of the characteristic equation should lie on the jÊ axis.

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Stability analysis If the Nyquist path in the s plane encircles Z zeros and P poles of 1+G(s)H(s) and does not pass through any poles or zeros of 1+G(s)H(s) as a representative point s moves in the clockwise direction along the Nyquist path, then the corresponding contour in the G(s)H(s) plane encircles the -1+j0 point N=Z-P times in the clockwise direction. In examining the stability of linear control systems using the Nyquist stability criterion, we see that three possibilities can occur: – There is no encirclement of the -1+j0 point. This implies that the system is stable if there are no poles of G(s)H(s) in the right-half s plane; otherwise, the system is unstable.

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– There are one or more counterclockwise encirclements of the -1+j0 point. In this case the system is stable if the number of counterclockwise encirclements is the same as the number of poles of G(s)H(s) in the right-half s plane; otherwise, the system is unstable. – There are one or more clockwise encirclements of the -1+j0 point. In this case the system is unstable.

8

Bode diagrams

A Bode diagram consists of two graphs: One is a plot of the logarithm of the magnitude of a sinusoidal transfer function; the other is a plot of the phase angle; both are plotted against the frequency on a logarithmic scale. The standard representation of the logarithmic magnitude of G(jÊ) is 20log | G(jv) |, where the base of the logarithm is 10. The main advantage of using the Bode diagram is that multiplication of magnitudes can be converted into addition. Furthermore, a simple method for sketching an approximate log-magnitude curve is available. It is based on asymptotic approximations. Such approximation by straightline asymptotes is sufficient if only rough information on the frequency-response characteristics is needed. Should the exact curve be desired, corrections can be made easily to these basic asymptotic plots. Expanding the low-frequency range by use of a logarithmic scale for the frequency is highly advantageous, since characteristics at low frequencies are most important in practical systems. Basic Factors of G( jÊ)H(jÊ). As stated earlier, the main advantage in using the logarithmic plot is the relative ease of plotting frequency-response curves. The basic factors that very frequently occur in an arbitrary transfer function G(jÊ)H(jÊ) are 1) Gain K

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2) Integral and derivative factors (jÊ)û1 3) First order factors (1 + jÊT )û1 4) Quadratic factors [1 + 2’( ÊjÊn ) + ( ÊjÊn )2 ]û1

Once we become familiar with the logarithmic plots of these basic factors, it is possible to utilize them in constructing a composite logarithmic plot for any general form of G(jÊ)H(jÊ) by sketching the curves for each factor and adding individual curves graphically, because adding the logarithms of the gains corresponds to multiplying them together. The Gain K A number greater than unity has a positive value in decibels, while a number smaller than unity has a negative value. The log-magnitude curve for a constant gain K is a horizontal straight line at the magnitude of 20 log K decibels.The phase angle of the gain K is zero. The effect of varying the gain K in the transfer function is that it raises or lowers the log-magnitude curve of the transfer function by the corresponding constant amount, but it has no effect on the phase curve. The decibel value of any number can be obtained from this line. As a number increases by a factor of 10, the corresponding decibel value increases by a factor of 20. This may be seen from the following:

Similarly,

20log(K ◊ 10) = 20logK + 20 20log(K ◊ 10n ) = 20logK + 20n

shop.ssb cra ck.com 20logK = ≠20log

1 K

Integral and Derivative Factors (jÊ)û . The logarithmic magnitude of 1/jÊ in decibel is 20log |

1 |= ≠20logÊ dB jÊ

The phase angle of 1/jÊ is constant and equal to ≠900 . First-Order Factors (1 + jÊT )û1 The log magnitude of the first-order factor is 20log |

 1 |= ≠20log 1 + Ê 2 T 2 dB 1 + jÊT

For low frequencies, such that Ê << 1/T , the log magnitude may be approximated by ≠20log



1 + Ê 2 T 2 dB = ≠20log1 = 0 dB

Thus, the log-magnitude curve at low frequencies is the constant 0-dB line. For high frequencies, such that Ê >> 1/T , ≠20log

Dec-2014



1 + Ê 2 T 2 dB = ≠20logÊT dB

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Quadratic factors [1 + 2’( ÊjÊn ) + ( ÊjÊn )2 ]û1 Control systems often possess quadratic factors of the form G(jÊ) =

1 [1 + 2’( ÊjÊn ) + ( ÊjÊn )2 ]û1

If ’ > 1, this quadratic factor can be expressed as a product of two first-order factors with real poles. If 0 < ’ < 1, this quadratic factor is the product of two complex- conjugate factors. Asymptotic approximations to the frequency-response curves are not accurate for a factor with low values of ’. The asymptotic frequency-response curve may be obtained as follows: G(jÊ) = ≠20log

Û

(1 ≠

Ê2 2 Ê ) + (2’ )2 Ên2 Ên

for low frequencies such that Ê << Ên , the log magnitude becomes ≠20log1 = 0dB The low-frequency asymptote is thus a horizontal line at 0 dB. For high frequencies such that Ê >> Ên , the log magnitude becomes ≠20log

Ê2 Ê = ≠40log 2 Ên Ên

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The high-frequency asymptote intersects the low-frequency one at Ê = Ên , since at this frequency -40log1 = 0 dB

This frequency, Ên , is the corner frequency for the quadratic factor considered.

8.1

Bode plot

Bode plot is the graphical tool for drawing the frequency response of a system. It is represented by two separate plots, one is the magnitude vs frequency and the other one is phase vs frequency.The magnitude is expressed in dB and the frequency is generally plotted in log scale. One of the advantages of the Bode plot in s-domain is that the magnitude curve can be approximated by straight lines which allows the sketching of the magnitude plot without exact computation. we use bi-linear transformation to transform unit circle of the z-plane into the imaginary axis of another complex plane, w plane, where w=

9

1 ln(z) T

Root loci

Consider the negative feedback system shown in Figure below. The closed-loop transfer function is

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The characteristic equation for this closed-loop system is 1 + G(s)H(s) = 0 G(s)H(s) = ≠1 Angle condition: ”

G(s)H(s) = ±180o (2k + 1)

k = 0, 1, 2...

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Magnitude condition:

| G(s)H(s) |= 1

The values of s that fulfill both the angle and magnitude conditions are the roots of the characteristic equation, or the closed-loop poles. A locus of the points in the complex plane satisfying the angle condition alone is the root locus. The roots of the characteristic equation (the closedloop poles) corresponding to a given value of the gain can be determined from the magnitude condition. The details of applying the angle and magnitude conditions to obtain the closed-loop poles are presented later in this section. A typical procedure for sketching the root-locus plot is as follows: 1. Determine the root loci on the real axis. The first step in constructing a root-locus plot is to locate the open-loop poles, s=0, s=1, and s=-2, in the complex plane. (There are no open- loop zeros in this system.) The locations of the open-loop poles are indicated by crosses. (The locations of the open-loop zeros in this book will be indicated by small circles.) Note that the starting points of the root loci (the points corresponding to K=0) are open-loop poles. The number of individual root loci for this system is three, which is the same as the number of open-loop poles. To determine the root loci on the real axis, we select a test point, s. If the test point is on the positive real axis, then ”

s = ” (s + 1) = ” (s + 2) = 0o

This shows that the angle condition cannot be satisfied. Hence, there is no root locus on the positive real axis. Next, select a test point on the negative real axis between 0 and -1. Then ”

Dec-2014

s = 180o , ” (s + 1) = ” (s + 2) = 0o Control Engineering

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shop.ssbcrack.com Thus, ≠” s ≠ ” (s ≠ 1) ≠ ” (s ≠ 2) = ≠180o

and the angle condition is satisfied. Therefore, the portion of the negative real axis between 0 and -1 forms a portion of the root locus. If a test point is selected between -1 and -2, then ”

s = ” (s + 1) = 1800 ”

(s + 2) = 0o

and ≠” s ≠ ” (s ≠ 1) ≠ ” (s ≠ 2) = ≠360o

2. Determine the asymptotes of the root loci The asymptotes of the root loci as s approaches infinity can be determined as follows: If a test point s is selected very far from the origin, then

shop.ssb cra ck.com k K = lim 3 sæŒ s(s + 1)(s + 2) sæŒ s

lim G(s) = lim

sæŒ

and the angle condition becomes ≠3/s = ±180o (2k + 1)

(k = 0, 1, 2, ...)

or Anglesof asymptotes =

±180o (2k = 1) 3

(k = 0, 1, 2, 3....)

3. Determine the breakaway point To plot root loci accurately, we must find the breakaway point, where the root-locus branches originating from the poles at 0 and -1 break away (as K is increased) from the real axis and move into the complex plane. The breakaway point corresponds to a point in the s plane where multiple roots of the characteristic equation occur. A simple method for finding the breakaway point is available. We shall present this method in the following: Let us write the characteristic equation as f (s) = B(s) + KA(s) = 0

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(9.1)

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where A(s) and B(s) do not contain K. Note that f(s)=0 has multiple roots at points where df (s) =0 ds This can be seen as follows: Suppose that f(s) has multiple roots of order r, where r Ø 2 .Then f(s) may be written as

shop.ssb cra ck.com f (s) = (s ≠ s1 )(s ≠ s2 )....(s ≠ sn )

Now we differentiate this equation with respect to s and evaluate df (s)/dsats = s1 . Then we get df (s) |s=s1 = 0 ds

(9.2)

This means that multiple roots of f(s) will satisfy equation (9.2) from equation (9.2) df (s) = B Õ (s) + KAÕ (s) = 0 ds where AÕ (s) =

dA(s) , ds

B Õ (s) =

dB(s) ds

The particular value of K that will yield multiple roots of the characteristic equation is K=≠

B Õ (s) AÕ (s)

If we substitute this value of K into equation (9.1), we get f (s) = B(s) ≠

B Õ (s) A(s) = 0 AÕ (s)

or B(s)AÕ (s) ≠ B Õ (s)A(s) = 0

(9.3)

If Equation (9.3) is solved for s, the points where multiple roots occur can be obtained. On the other hand, from Equation (9.1) we obtain Dec-2014

Control Engineering

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K=≠

B(s) A(s)

and dK B Õ (s)A(s) ≠ B(s)AÕ (s) =≠ ds A2 (s) Therefore, the breakaway points can be simply determined from the roots of dK =0 ds

10

Lead compensation

– A lead compensator is a device that provides phase lead in its’ frequency response. – If the compensator has phase lead - and never a phase lag - then there are implications about where the corner frequencies are in the Bode’ plot. – Other implications are that the phase lead compensator will have only certain types of pole-zero patterns in the s plane. A lead compensator will have a transfer function of the form: G(jÊ) =

jÊ jÊp jÊ jÊz

+1 +1

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Since a lead compensator has only positive phase angle, we must have: Êz < Ê ≠ p

11

Lag compensation

lag compensatorâ ès can be used to adjust frequency response by adding equal numbers of poles and zeroes to a systems. Those added singularities may possibly be manipulated to give better stability, better performance and general improvement. – First, a lag compensator is a device that provides phase lag in its’ frequency response. – If the compensator has phase lag - and never a phase lead - then there are implications about where the corner frequencies are in the Bode’ plot. – Phase lag compensator will have only certain types of pole-zero patterns in the s plane.

12

lead-lag compensation

In a lag lead compensator, where a lag compensator is cascaded with a lead compensator, both steady state and transient responses can be improved. Both lead compensators and lag compensators introduce a pole-zero pair into the open loop transfer function. The transfer function can be written in the Laplace domain as Y s+z = X s+p where X is the input to the compensator, Y is the output, s is the complex Laplace transform variable, z is the zero frequency and p is the pole frequency. The pole and zero are both typically Dec-2014

Control Engineering

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negative, or left of the zero in the complex plane. In a lead compensator, | z |<| p |, while in a lag compensator | z |>| p |. A lead-lag compensator consists of a lead compensator cascaded with a lag compensator. The overall transfer function can be written as Y (s + z1 )(s + z2 ) = X (s + p1 )(s + p2 )

13

State space model

State models are basically time domain models where we are interested in the dynamics of some characterizing variables called state variables which along with the input represent the state of a system at a given time. State: The state of a dynamic system is the smallest set of variables, xÁRn ,such that given x(to ) and u(t), t > to , x(t), t > to can be uniquely determined. Usually a system governed by a nth order differential equation or nth order transfer function is expressed in terms of n state variables: x1 , x2 , .......xn . The generic structure of a state-space model of a nth order continuous time dynamical system with m input and p output is given by: x. (t) = Ax(t) + Bu(t) y(t) = Cx(t) + Du(t)

13.1

State equation Output equation

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State-transition matrix

We can describe above equation in terms of a matrix function properties:

(t, · ) that has the following two

„. (t, · ) = A(t) (t, · ) (·, · ) = I This matrix function is referred to as the state transition matrix, and under our assumption on the nature of A(t) it turns out that the state transition matrix exists and is unique.

14

Controllability and observability

Controllability: In order to be able to do whatever we want with the given dynamic system under control input, the system must be controllable. Observability: In order to see what is going on inside the system under observation, the system must be observable. Controllability deals with the possibility of forcing the system to a particular state by application of a control input. If a state is uncontrollable then no input will be able to control that state. On the other hand whether or not the initial states can be observed from the output is determined using observability property. Thus if a state is not observable then the controller will not be able to determine its behavior from the system output and hence not be able to use that state to stabilize the system.

Dec-2014

Control Engineering

Engineering'Knowledge'TEst'

'

Control'Engineering'MCQs'

Control'Engineering'MCQs' ! 1.''Which'statement'is'not'correct'for'open

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8.''The'frequency'and'time'domain'are'related'through' (a)' Laplace'transform' (b)' Fourier'integral' (c)' Laplace'transform'of'Fourier' (d)' Laplace'transform'and'Fourier' integral' integral' ' 9.''The'characteristic'equation'of'a'second'order'system'is'given'by'! " + 2%&' ! + &'" = 0.'The'term'&' 'is'called' (a)' Overdamped'natural'frequency' (b)' Undamed'natural'frequency' (c)' Undamped'critical'frequency' (d)' None'of'these' ' 10.'In'the'above'equation,'the'term'ξ'is'called' (a)' Pole'factor' (b)' Stability'factor'' (c)' Damping'factor' (d)' Frequency'factor' ' 11.''In'the'above'system,'if'ξ=1,'the'poles'of'the'transfer'function'will'be' (a)' Real'and'equal'' (b)' Imaginary'and'equal' (c)' Complex'conjugate' (d)' Over'damped' 12.''In'the'same'system,'if'ξ'='1,'the'system'is' (a)' Underdamped' (b)' Absolutely'damped' (c)' Critically'damped' (d)' Overdamped' ' 13.''In'the'system,'if'ξ'='1,'the'system'exhibits' (a)' Large'undershoot' (b)' Large'overshoot' (c)' Small'overshoot' (d)' No'overshoot' ' 14.'In'the'same'system,'if'ξ'>'1,'the'poles'are' (a)' Real'and'equal' (b)' Complex'conjugate' (c)' Imaginary'and'equal' (d)' None'of'these' ' 15.''In'the'same'system,'if'ξ'>'1,'the'system'is' (a)' Underdamped'' (b)' Absolutely'damped' (c)' Critically'damped' (d)' Overdamped' ' 16.''In'the'same'system,'If'ξ'>1,'the'system'exhibits'' (a)' Large'overshoot' (b)' Medium'overshoot' (c)' Small'overshoot' (d)' No'overshoot' ' ' '


'


17.'In'the'same'system'if,'ξ'<'1,'the'poles'are' (a)' Real'and'equal' (b)' Real'and'unequal' (c)' Imaginary'and'equal' (d)' Complex'conjugate' ' 18.''In'the'same'system,'if'ξ'<'1,'the'system'will'exhibit' (a)' Damped'response'' (b)' Oscillatory'response' (c)' An'overshoot' (d)' All'of'these' ' 19.''In'the'same'system','if'ξ'='0,'the'poles'are' (a)' ±+&' ' (b)' ±+&'" ' (c)' ±+%&' ' (d)' ±+%&'" ' ' 20.''Error'constants'of'system'are'a'measure'of'' (a)' Steady
(b)' Velocity'input'signal' (d)' All'of'these'

' 22.''Velocity'error'constant'of'a'system'is'measured'when'the'input'of'the'system'is' (a)' Unit'step'function' (b)' Unit'ramp'function' (c)' Unit'impulse'function' (d)' Unit'parabolic'function' ' 23.''Bandwidth'is'used'as'means'of'specifying'performance'of'a'control'system'related' to' (a)' Relative'stability'of'the'system' (b)' The'speed'of'the'response' (c)' The'constant'gain' (d)' All'of'these' ' 24.''In'control'systems,'excessive'bandwidth'should'be'avoided'because' (a)' Noise'is'proportional'to' (b)' It'leads'to'low'relative'stability' bandwidth' (c)' It'leads'to'slow'speed'of'response' (d)' None'of'these' ' ' '


'


25.''Settling'time'of'a'second

'


33.''The'transfer'function'of'a'rate'controller'is'of'the'type' (a)' 01 ' (c)' 1 ' /!

(b)' /!' 1 (d)' ' /! + 1

' 34.''The'position'error'coefficient'for'an'unity'feedback'system'is'defined'as' 7(!) (a)' (b)' lim 7(!)' 5→' lim ' 5→' ! (c)' lim !7(!)' (d)' :;<=>;?>@ℎ=!=' 5→'

' 35.''The'velocity'error'coefficient'for'an'unity'feedback'system'is'defined'as' 7(!) (a)' (b)' lim 7(!)' 5→' lim ' 5→' ! ' (c)' lim !7(!)' (d)' :;<=>;?>@ℎ=!=' 5→'

' 36.''The'acceleration'error'coefficient'for'an'unity'feedback'system'is'defined'as' 7(!) (a)' (b)' lim 7(!)' 5→' lim ' 5→' ! (c)' lim !7(!)' (d)' :;<=>;?>@ℎ=!=' 5→'

' 37.''For'any'given'closed
(b)' All'the'coefficients'are'always'non< zero' ' (d)' None'of'these'

(b)' No'pole'at'the'origin' (d)' Two'poles'at'the'origin' (b)' Net'pole'at'the'origin' (d)' Two'poles'at'the'origin' (b)' Net'pole'at'the'origin' (d)' Two'poles'at'the'origin'


'


41.'Conditionally'stable'system'is'one'which'exhibits'poor'stability'at' (a)' Increased'values'of'open
5 DE5

(b)' Type<1'system' (d)' Type<3'system'

' 44.''In'the's

(c)' Elements'of'the'first'row'are'of' opposite'sign'alternatively'

'


(d)' Elements'of'the'first'column'are'of' opposite'sign'alternatively'

' 49.''In'Routh
(a)' <20'dB/decade' (c)' 6'dB/decade'

(b)' +20'dB/decade' (d)' <6'dB/decade'

' 54.''Phase'margin'of'a'system'is'used'to'specify' (a)' Relative'stability' (b)' Absolute'stability' (c)' Time'response' (d)' Frequency'response' '


'


55.''Gain'margin'is'the'reciprocal'of'gain'at'the'frequency'at'which'the'phase'angle' become' (a)' 0°' (b)' 90°' (c)' 180°' (d)' 270°' 56.''Gain'cross'over'frequency'is'defined'as' (a)' │7 +& J(+&│ = 1' (b)' │7 +& J(+&│ = 0' 1 (c)' │7 +& J(+&│ = K' (d)' │7 +& J(+&│ = ' 2 ' 57.''A'position

64.''Given,'7 ! =

D 5 DEM5

'


,'the'system'is'

(a)' Stable' (c)' Marginally'stable'

(b)' Unstable' (d)' Unconditionally'stable'

' 65.''Sinusoidal'oscillators'are'' (a)' Stable' (b)' Marginally'stable' (c)' Unstable' (d)' Conditionally'stable' ' 66.''The'gain'of'a'system'is'10'at'some'frequency.'In'terms'of'dB,'it'is' (a)' 0'dB' (b)' 1'dB' (c)' 20'dB' (d)' 100'dB' ' 67.''If'the'gain'of'the'open

'


73.''The'frequency'and'time'domain'are'related'through' (a)' Laplace'transform' (b)' Fourier'integral' (c)' Laplace'transform'or'Fourier' (d)' Laplace'transform'and'Fourier' integral' integral' ' 74.''The'Laplace'transform'of'unit'step'function'and'ramp'functions'respectively'are' 1 1 1 1 (a)' (b)' , ' , ' !" ! ! !" 1 1 1 1 (c)' (d)' , P' , ' ! ! !P ! ' 75.''The'inverse'Laplace'transform'of'2/(1+s)'is' (a)' 2 @ + 1 ' (b)' 2= QR ' (c)' 2=' (d)' 2= Q"R ' ' 76.''The'characteristic'equation'of'a'second

'


81.''Adding'of'poles'in'the'transfer'function'causes' (a)' Lag'compensation' (b)' Lead'compensation' (c)' Lead'lag'compensation' (d)' None'of'these' ' 82.''Adding'of'zeros'in'transfer'function'causes' (a)' Lag'compensation' (b)' Lead'compensation' (c)' Lead'lag'compensation' (d)' None'of'these' ' 83.''The'best'method'for'determining'the'stability'and'transient'response'is' (a)' Bode'plot' (b)' Nyquist'plot' (c)' Root'locus' (d)' None'of'these' ' 84.''Which'of'the'following'elements'is'not'used'in'an'automatic'control'system?' (a)' Sensor' (b)' Error'detector' (c)' Oscillator' (d)' Final'control'element' ' T 85.''A'unity'feedback'system'has'transfer'function'7 ! = ,'is' (a)' Natural'frequency'='9' (c)' Damping'ratio'='0.6'

5 5EP

(b)' Natural'Frequency'='3' (d)' Damping'ratio'='0.8'

' 86.''The'transfer'function'of'a'unity'feedback'system'is'7 ! =

B 5 5ED 5EN

.'The'range'of'

k'for'stable'operation'is'' (a)' 040' (c)' k>0' (d)' none'of'these' ' 87.''The'characteristic'equation'of'a'unity'feedback'system'is'given'by'! P + ! " + 4! + 4 = 0'is' (a)' The'system'has'one'pole'in'RH's< (b)' The'system'has'no'pole'in'RH's

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89.''Laplace'transform'of'the'functions'= QR 'and'= Q"R 'are' 1 1 1 1 (a)' (b)' , ' , ' !+1 !+2 !−1 !−2 1 1 (c)' (d)' <;<=>;?>@ℎ=>VWX=<' , ' !+1 !−2 ' 90.''The'inverse'Laplace'Transform'of'2/(s+1)'is' (a)' 2 @ + 1 ' (b)' 2= QR ' (c)' 2= R ' (d)' = Q"R ' ' 91.''The'zeros'of''Y ! = (a)' s=16,0' (c)' s=<4,4'

5 C QDM

5E" 5EZ

' (b)' s=4,3' (d)' s=<2,<4'

' 92.''The'main'application'of'transfer'function'is'in'the'study'of' (a)' Steady'state'behavior'of'systems' (b)' Steady'state'as'well'as'transient' behavior'of'systems' (c)' Only'transient'behavior'of' (d)' None'of'these' systems' ' 93.''The'transient'response'of'a'system'is'mainly'due'to'' (a)' Internal'forces' (b)' Inertia'forces' (c)' Friction' (d)' Stored'energy' ' 94.''Two'blocks'having'respective'functions'as'G1'and'G2'are'connected'in'series' cascade.'Their'resultant'will'be' (a)' G1G2' (b)' G1+G2' (c)' G1/G2' (d)' G2/G1' ' 95.''Damping'is'proportional'to' (a)' V[W<> (b)' 1/V[W<> (c)' (d)' 1/ V[W<' V[W<' ' 96.''Which'of'the'following'is'used'for'Nyquist'plot?' (a)' Characteristic'equation' (b)' Closed'loop'function' (c)' Open'loop'function' (d)' None'of'the'above' ' ' '


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97.''With'feedback'system' (a)' The'transient'response'gets' (b)' The'transient'response'decays'at'a' magnified' constant'rate' (c)' The'transient'response'decays' (d)' The'transient'response'decays'more' slowly' quickly' ' 98.''An'ideal'potentiometer'should'have' (a)' A'fine'wire' (b)' Zero'resolution' (c)' An'infinite'resolution' (d)' None'of'these' ' 99.''The'resolution'of'potentiometer'should'be' (a)' Zero' (b)' Low' (c)' Very'high' (d)' Infinity' ' 100.'One'of'the'disadvantages'of'a'servomotor'is'that' (a)' It'has'low'starting'torque' (b)' It'develops'commutation'problem' (c)' It'has'low'reliability' (d)' It'can'handle'only'light'loads' ' 101.'A'techno] = ^] + _`'is'given'by' (a)' = aR ' (b)' = QbR ' (c)' 1 aR (d)' 1 QaR = ' = ' 2 2 ' 104.'Which'of'the'following'system'provides'excellent'transient'as'well'as'steady

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105.'The'value'of'compressed'air'used'in'pneumatic'instrumentation'system'is' (a)' 1>cV/de" ' (b)' 1.4>cV/de" ' (c)' 2>cV/de" ' (d)' 6>cV/de" ' ' 106.'The'medium'in'pneumatic'system'is' (a)' Liquid' (b)' Air' (c)' Oil' (d)' Helium' ' 107.'In'pneumatic'systems,'electrical'resistance'is'analogous'to'a'' (a)' Restriction'to'flow' (b)' Volume'of'air' (c)' Restriction'to'flow' (d)' Volume'of'air' ' 108.'In'pneumatic'systems,'electrical'capacitance'is'analogous'to' (a)' Restriction'to'flow' (b)' Volume'of'air' (c)' Filled'helical'tube' (d)' None'of'these' ' 109.'Which'of'the'following'elements'is'not'used'in'an'automatic'control'system?' (a)' Sensor' (b)' Error'detector' (c)' Oscillator' (d)' Final'control'element' ' 110.'The'output'of'the'controller'in'a'control'system'is'given'to' (a)' Sensor' (b)' Comparator' (c)' Amplifier' (d)' Final'control'element' ' 111.'The'input'to'a'controller'is'a' (a)' Sensed'signal' (b)' Error'signal' (c)' Desired'variable'value' (d)' Servo'signal' ' 112.'The'error'signal'is' (a)' The'sum'of'measured'value'and' (b)' The'difference'between'measured' set'value' value'and'set'value' (c)' The'ratio'of'measured'value'and' (d)' The'difference'between'set'value'and' desired'value' output'of'final'control'elements' ' 113.'Essentially'a'controller'is'a' (a)' Comparator' (b)' Clipper' (c)' Amplifier' (d)' Sensor' ' ' '


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114.'Which'of'the'following'sequence'is'correct'for'a'three
84'(c)'

85'(b)'

86'(a)'

87'(b)'

88.'(c)' 89.'(a)' 90.'(b)'

91.'(c)' 92.'(b)' 93.'(d)' 94.'(a)' 95.'(d)' 96.'(c)' 97.'(c)' 98.'(c)' 99.'(d)' 100.(a)' 101.(b)' 102.(a)' 103.(a)' 104.(d)' 105.(b)' 106.(b)' 107.(a)' 108.(b)' 109.(c)' 110.(d)' 111.(b)' 112.(b)' 113.(a)' 114.(d)' ' '

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Telecommunication systems

Contents 1 Amplitude modulation

1

2 Superheterodyne receiver

3

3 Signal-to-noise ratio

3

4 Channel capacity theorem

5

5 Pulse-code modulation

6

6 Differential pulse-code modulation

7

7 Digital and Analog modulation schemes

7

8 TDMA: Time division multiple access

12

9 FDMA: Frequency-division multiple access

13

10 CDMA: Code division multiple access

14

11 Code division multiplexing (synchronous CDMA)

15

12 Fundamentals of mobile communication

16

13 Fundamentals of optical fibre communication

19

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1

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1

Amplitude modulation • Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength (amplitude) of the carrier in proportion to the waveform being sent. That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker, or the light intensity of television pixels. • This contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its phase is varied, by the modulating signal. • AM was the earliest modulation method used to transmit voice by radio. It was developed during the first two decades of the 20th century beginning with Reginald Fessenden’s radiotelephone experiments in 1900. It remains in use today in many forms of communication; for example it is used in portable two way radios, VHF aircraft radio and in computer modems.[citation needed] ”AM” is often used to refer to mediumwave AM radio broadcasting. • In amplitude modulation, the amplitude or ”strength” of the carrier oscillations is what is varied. For example, in AM radio communication, a continuous wave radio-frequency signal (a sinusoidal carrier wave) has its amplitude modulated by an audio waveform before transmission. The audio waveform modifies the amplitude of the carrier wave and determines the envelope of the waveform. In the frequency domain, amplitude modulation produces a signal with power concentrated at the carrier frequency and two adjacent sidebands. Each sideband is equal in bandwidth to that of the modulating signal, and is a mirror image of the other. Standard AM is thus sometimes called ”double-sideband amplitude modulation” (DSB-AM) to distinguish it from more sophisticated modulation methods also based on AM.

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Disadvantage of amplitude modulation techniques

• One disadvantage of all amplitude modulation techniques (not only standard AM) is that the receiver amplifies and detects noise and electromagnetic interference in equal proportion to the signal. Increasing the received signal to noise ratio, say, by a factor of 10 (a 10 decibel improvement), thus would require increasing the transmitter power by a factor of 10. This is in contrast to frequency modulation (FM) and digital radio where the effect of such noise following demodulation is strongly reduced so long as the received signal is well above the threshold for reception. For this reason AM broadcast is not favored for music and high fidelity broadcasting, but rather for voice communications and broadcasts (sports, news, talk radio etc.)



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• Another disadvantage of AM is that it is inefficient in power usage; at least two-thirds of the power is concentrated in the carrier signal. The carrier signal contains none of the original information being transmitted (voice, video, data, etc.). However its presence provides a simple means of demodulation using envelope detection, providing a frequency and phase reference to extract the modulation from the sidebands.

2

Superheterodyne receiver

In electronics, a superheterodyne receiver (often shortened to superhet) uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original radio carrier frequency. It was invented by US engineer Edwin Armstrong in 1918 during World War I. Virtually all modern radio receivers use the superheterodyne principle. At the cost of an extra frequency converter stage, the superheterodyne receiver provides superior selectivity and sensitivity compared with simpler designs.

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Design and principle of operation

The principle of operation of the superheterodyne receiver depends on the use of heterodyning or frequency mixing. The signal from the antenna is filtered sufficiently at least to reject the image frequency (see below) and possibly amplified. A local oscillator in the receiver produces a sine wave, which mixes with that signal, shifting it to a specific intermediate frequency (IF), usually a lower frequency. The IF signal is itself filtered and amplified and possibly processed in additional ways. The demodulator uses the IF signal rather than the original radio frequency to recreate a copy of the original information (such as audio).

The diagram above shows the minimum requirements for a single-conversion superheterodyne receiver design. The following essential elements are common to all superheterodyne circuits: a receiving antenna; a tuned stage, which may optionally contain amplification (RF amplifier); a variable frequency local oscillator; a frequency mixer; a band pass filter and intermediate frequency (IF) amplifier; and a demodulator plus additional circuitry to amplify or process the original audio signal (or other transmitted information).

Circuit description To receive a radio signal, a suitable antenna is required. This is often built into a receiver, especially in the case of AM broadcast band radios. The output of the antenna may be very



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small, often only a few microvolts. The signal from the antenna is tuned and may be amplified in a so-called radio frequency (RF) amplifier, although this stage is often omitted. One or more tuned circuits at this stage block frequencies that are far removed from the intended reception frequency. In order to tune the receiver to a particular station, the frequency of the local oscillator is controlled by the tuning knob (for instance). Tuning of the local oscillator and the RF stage may use a variable capacitor, or varicap diode. The tuning of one (or more) tuned circuits in the RF stage must track the tuning of the local oscillator. Notice that the accompanying diagram shows a fixed-frequency local oscillator, as the symbol is for a fixed-frequency crystal frequency-determining device. A tuneable receiver would show a variable-frequency oscillator with operational connection to the tuned circuits of the antenna and radio-frequency amplifier stages.

3

Signal-to-noise ratio

Signal-to-noise ratio (often abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can be applied to any form of signal (such as isotope levels in an ice core or biochemical signaling between cells). The signal-to-noise ratio, the bandwidth, and the channel capacity of a communication channel are connected by the Shannon-Hartley theorem. Signal-to-noise ratio is sometimes used informally to refer to the ratio of useful information to false or irrelevant data in a conversation or exchange. For example, in online discussion forums and other online communities, off-topic posts and spam are regarded as ”noise” that interferes with the ”signal” of appropriate discussion.

Definition

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Signal-to-noise ratio is defined as the power ratio between a signal (meaningful information) and the background noise (unwanted signal): SNR =

Psignal , Pnoise

where P is average power. Both signal and noise power must be measured at the same or equivalent points in a system, and within the same system bandwidth. If the variance of the signal and noise are known, and the signal is zero-mean: SNR =

2 ‡signal . 2 ‡noise

If the signal and the noise are measured across the same impedance, then the SNR can be obtained by calculating the square of the amplitude ratio: Psignal SNR = = Pnoise

3

Asignal Anoise

42

,

where A is root mean square (RMS) amplitude (for example, RMS voltage). Because many signals have a very wide dynamic range, SNRs are often expressed using the logarithmic decibel scale. In decibels, the SNR is defined as 3 4 Psignal SNRdB = 10 log10 = Psignal,dB ≠ Pnoise,dB , Pnoise which may equivalently be written using amplitude ratios as C3 42 D 3 4 Asignal Asignal SNRdB = 10 log10 = 20 log10 . Anoise Anoise



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The concepts of signal-to-noise ratio and dynamic range are closely related. Dynamic range measures the ratio between the strongest un-distorted signal on a channel and the minimum discernible signal, which for most purposes is the noise level. SNR measures the ratio between an arbitrary signal level (not necessarily the most powerful signal possible) and noise. Measuring signal-to-noise ratios requires the selection of a representative or reference signal. In audio engineering, the reference signal is usually a sine wave at a standardized nominal or alignment level, such as 1 kHz at +4 dBu (1.228 VRMS). SNR is usually taken to indicate an average signal-to-noise ratio, as it is possible that (near) instantaneous signal-to-noise ratios will be considerably different. The concept can be understood as normalizing the noise level to 1 (0 dB) and measuring how far the signal ’stands out’.

SNR for various modulation systems • Amplitude modulation

Channel signal-to-noise ratio is given by (SNR)C,AM =

A2c (1 + ka2 P ) 2W N0

where W is the bandwidth and ka is modulation index Output signal-to-noise ratio (of AM receiver) is given by (SNR)O,AM =

A2c ka2 P 2W N0

• Frequency modulation

Channel signal-to-noise ratio is given by

shop.ssb cra ck.com A (SNR)C,FM =

2 c

2W N0

Output signal-to-noise ratio is given by (SNR)O,FM =

A2c kf2 P 2N0 W 3

Digital signals When a measurement is digitized, the number of bits used to represent the measurement determines the maximum possible signal-to-noise ratio. This is because the minimum possible noise level is the error caused by the quantization of the signal, sometimes called Quantization noise. This noise level is non-linear and signal-dependent; different calculations exist for different signal models. Quantization noise is modeled as an analog error signal summed with the signal before quantization (”additive noise”). This theoretical maximum SNR assumes a perfect input signal. If the input signal is already noisy (as is usually the case), the signal’s noise may be larger than the quantization noise. Real analog-to-digital converters also have other sources of noise that further decrease the SNR compared to the theoretical maximum from the idealized quantization noise, including the intentional addition of dither. Although noise levels in a digital system can be expressed using SNR, it is more common to use Eb /No , the energy per bit per noise power spectral density. The modulation error ratio (MER) is a measure of the SNR in a digitally modulated signal.



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Effect of bandwidth on SNR A number of other factors apart from the basic performance of the set can affect the signal to noise ratio, SNR specification. The first is the actual bandwidth of the receiver. As the noise spreads out over all frequencies it is found that the wider the bandwidth of the receiver, the greater the level of the noise. Accordingly the receiver bandwidth needs to be stated. Additionally it is found that when using AM the level of modulation has an effect. The greater the level of modulation, the higher the audio output from the receiver. When measuring the noise performance the audio output from the receiver is measured and accordingly the modulation level of the AM has an effect. Usually a modulation level of 30

4

Channel capacity theorem

In information theory, the Shannon-Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise. It is an application of the noisy-channel coding theorem to the archetypal case of a continuous-time analog communications channel subject to Gaussian noise. The theorem establishes Shannon’s channel capacity for such a communication link, a bound on the maximum amount of error-free digital data (that is, information) that can be transmitted with a specified bandwidth in the presence of the noise interference, assuming that the signal power is bounded, and that the Gaussian noise process is characterized by a known power or power spectral density. The law is named after Claude Shannon and Ralph Hartley. Statement of the theorem: Considering all possible multi-level and multi-phase encoding techniques, the Shannon-Hartley theorem states the channel capacity C, meaning the theoretical tightest upper bound on the information rate (excluding error correcting codes) of clean (or arbitrarily low bit error rate) data that can be sent with a given average signal power S through an analog communication channel subject to additive white Gaussian noise of power N, is: 3 4 S C = B log2 1 + N

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Where

• C is the channel capacity in bits per second;

• B is the bandwidth of the channel in hertz (passband bandwidth in case of a modulated signal); • S is the average received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e. modulated carrier), measured in watts (or volts squared); • N is the average noise or interference power over the bandwidth, measured in watts (or volts squared); and • S/N is the signal-to-noise ratio (SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the Gaussian noise interference expressed as a linear power ratio (not as logarithmic decibels).

5

Pulse-code modulation

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, Compact Discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. A PCM stream has two basic properties that determine the stream’s fidelity to the original analog signal: the sampling rate, which is the number of times per second that samples are



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taken; and the bit depth, which determines the number of possible digital values that can be used to represent each sample.

Modulation

In the diagram above, a sine wave (red curve) is sampled and quantized for PCM. The sine wave is sampled at regular intervals, shown as vertical lines. For each sample, one of the available values (on the y-axis) is chosen by some algorithm. This produces a fully discrete representation of the input signal (blue points) that can be easily encoded as digital data for storage or manipulation. For the sine wave example at right, we can verify that the quantized values at the sampling moments are 8, 9, 11, 13, 14, 15, 15, 15, 14, etc. Encoding these values as binary numbers would result in the following set of nibbles: 1000(23 ◊1+22 ◊0+21 ◊0+20 ◊0 = 8 + 0 + 0 + 0 = 8), 1001, 1011, 1101, 1110, 1111, 1111, 1111, 1110, etc. These digital values could then be further processed or analyzed by a digital signal processor. Several PCM streams could also be multiplexed into a larger aggregate data stream, generally for transmission of multiple streams over a single physical link. One technique is called time-division multiplexing (TDM) and is widely used, notably in the modern public telephone system. The PCM process is commonly implemented on a single integrated circuit generally referred to as an analog-to-digital converter (ADC).

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Demodulation To recover the original signal from the sampled data, a ”demodulator” can apply the procedure of modulation in reverse. After each sampling period, the demodulator reads the next value and shifts the output signal to the new value. As a result of these transitions, the signal has a significant amount of high-frequency energy caused by aliasing. To remove these undesirable frequencies and leave the original signal, the demodulator passes the signal through analog filters that suppress energy outside the expected frequency range (greater than the Nyquist frequency fs /2 ). The sampling theorem shows PCM devices can operate without introducing distortions within their designed frequency bands if they provide a sampling frequency twice that of the input signal. For example, in telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. Therefore, per the Nyquist-Shannon sampling theorem, the sampling frequency (8 kHz) must be at least twice the voice frequency (4 kHz) for effective reconstruction of the voice signal. The electronics involved in producing an accurate analog signal from the discrete data are similar to those used for generating the digital signal. These devices are Digital-to-analog converters (DACs). They produce a voltage or current (depending on type) that represents the value presented on their digital inputs. This output would then generally be filtered and amplified for use.



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6

Differential pulse-code modulation

Differential pulse-code modulation (DPCM) is a signal encoder that uses the baseline of pulsecode modulation (PCM) but adds some functionalities based on the prediction of the samples of the signal. The input can be an analog signal or a digital signal. If the input is a continuous-time analog signal, it needs to be sampled first so that a discretetime signal is the input to the DPCM encoder. • Option 1: take the values of two consecutive samples; if they are analog samples, quantize them; calculate the difference between the first one and the next; the output is the difference, and it can be further entropy coded. • Option 2: instead of taking a difference relative to a previous input sample, take the difference relative to the output of a local model of the decoder process; in this option, the difference can be quantized, which allows a good way to incorporate a controlled loss in the encoding. Applying one of these two processes, short-term redundancy (positive correlation of nearby values) of the signal is eliminated; compression ratios on the order of 2 to 4 can be achieved if differences are subsequently entropy coded, because the entropy of the difference signal is much smaller than that of the original discrete signal treated as independent samples.

7

Digital and Analog modulation schemes • In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted.

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• In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. Modulation of a sine waveform transforms a baseband message signal into a passband signal. • A modulator is a device that performs modulation. A demodulator (sometimes detector or demod) is a device that performs demodulation, the inverse of modulation. A modem (from modulator-demodulator) can perform both operations. • The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network (where a bandpass filter limits the frequency range to 300-3400 Hz), or over a limited radio frequency band. • The aim of analog modulation is to transfer an analog baseband (or lowpass) signal, for example an audio signal or TV signal, over an analog bandpass channel at a different frequency, for example over a limited radio frequency band or a cable TV network channel. • Analog and digital modulation facilitate frequency division multiplexing (FDM), where several low pass information signals are transferred simultaneously over the same shared physical medium, using separate passband channels (several different carrier frequencies). • The aim of digital baseband modulation methods, also known as line coding, is to transfer a digital bit stream over a baseband channel, typically a non-filtered copper wire such as a serial bus or a wired local area network. • The aim of pulse modulation methods is to transfer a narrowband analog signal, for example a phone call over a wideband baseband channel or, in some of the schemes, as a bit stream over another digital transmission system.



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Analog modulation methods In analog modulation, the modulation is applied continuously in response to the analog information signal. Common analog modulation techniques are: 1. Amplitude modulation (AM) (here the amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal) • Double-sideband modulation (DSB)

– Double-sideband modulation with carrier (DSB-WC) (used on the AM radio broadcasting band) – Double-sideband suppressed-carrier transmission (DSB-SC) – Double-sideband reduced carrier transmission (DSB-RC)

• Single-sideband modulation (SSB, or SSB-AM)

– SSB with carrier (SSB-WC) – SSB suppressed carrier modulation (SSB-SC)

• Vestigial sideband modulation (VSB, or VSB-AM) • Quadrature amplitude modulation (QAM)

2. Angle modulation, which is approximately constant envelope • Frequency modulation (FM) (here the frequency of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal) • Phase modulation (PM) (here the phase shift of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal)

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Digital modulation methods

In digital modulation, an analog carrier signal is modulated by a discrete signal. Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet).

Fundamental digital modulation methods The most fundamental digital modulation techniques are based on keying: • PSK (phase-shift keying): a finite number of phases are used.

• FSK (frequency-shift keying): a finite number of frequencies are used.

• ASK (amplitude-shift keying): a finite number of amplitudes are used.

• QAM (quadrature amplitude modulation): a finite number of at least two phases and at least two amplitudes are used. In QAM, an inphase signal (or I, with one example being a cosine waveform) and a quadrature phase signal (or Q, with an example being a sine wave) are amplitude modulated with a finite number of amplitudes, and then summed. It can be seen as a two-channel system, each channel using ASK. The resulting signal is equivalent to a combination of PSK and ASK. In all of the above methods, each of these phases, frequencies or amplitudes are assigned a unique pattern of binary bits. Usually, each phase, frequency or amplitude encodes an equal number of bits. This number of bits comprises the symbol that is represented by the particular phase, frequency or amplitude. If the alphabet consists of M = 2N alternative symbols, each symbol represents a message consisting of N bits. If the symbol rate (also known as the baud rate) is fS symbols/second (or baud), the data rate is N fS bit/second.



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For example, with an alphabet consisting of 16 alternative symbols, each symbol represents 4 bits. Thus, the data rate is four times the baud rate. In the case of PSK, ASK or QAM, where the carrier frequency of the modulated signal is constant, the modulation alphabet is often conveniently represented on a constellation diagram, showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-axis, for each symbol.

Modulator and detector principles of operation PSK and ASK, and sometimes also FSK, are often generated and detected using the principle of QAM. The I and Q signals can be combined into a complex-valued signal I+jQ (where j is the imaginary unit). The resulting so called equivalent lowpass signal or equivalent baseband signal is a complex-valued representation of the real-valued modulated physical signal (the so-called passband signal or RF signal). These are the general steps used by the modulator to transmit data: 1. Group the incoming data bits into codewords, one for each symbol that will be transmitted. 2. Map the codewords to attributes, for example amplitudes of the I and Q signals (the equivalent low pass signal), or frequency or phase values. 3. Adapt pulse shaping or some other filtering to limit the bandwidth and form the spectrum of the equivalent low pass signal, typically using digital signal processing. 4. Perform digital to analog conversion (DAC) of the I and Q signals (since today all of the above is normally achieved using digital signal processing, DSP). 5. Generate a high frequency sine carrier waveform, and perhaps also a cosine quadrature component. Carry out the modulation, for example by multiplying the sine and cosine waveform with the I and Q signals, resulting in the equivalent low pass signal being frequency shifted to the modulated passband signal or RF signal. Sometimes this is achieved using DSP technology, for example direct digital synthesis using a waveform table, instead of analog signal processing. In that case the above DAC step should be done after this step.

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6. Amplification and analog bandpass filtering to avoid harmonic distortion and periodic spectrum At the receiver side, the demodulator typically performs: 1. Bandpass filtering. 2. Automatic gain control, AGC (to compensate for attenuation, for example fading). 3. Frequency shifting of the RF signal to the equivalent baseband I and Q signals, or to an intermediate frequency (IF) signal, by multiplying the RF signal with a local oscillator sinewave and cosine wave frequency (see the superheterodyne receiver principle). 4. Sampling and analog-to-digital conversion (ADC) (Sometimes before or instead of the above point, for example by means of undersampling). 5. Equalization filtering, for example a matched filter, compensation for multipath propagation, time spreading, phase distortion and frequency selective fading, to avoid intersymbol interference and symbol distortion. 6. Detection of the amplitudes of the I and Q signals, or the frequency or phase of the IF signal. 7. Quantization of the amplitudes, frequencies or phases to the nearest allowed symbol values. 8. Mapping of the quantized amplitudes, frequencies or phases to codewords (bit groups). 9. Parallel-to-serial conversion of the codewords into a bit stream. Engineering Knowledge Test


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10. Pass the resultant bit stream on for further processing such as removal of any errorcorrecting codes. As is common to all digital communication systems, the design of both the modulator and demodulator must be done simultaneously. Digital modulation schemes are possible because the transmitter-receiver pair have prior knowledge of how data is encoded and represented in the communications system. In all digital communication systems, both the modulator at the transmitter and the demodulator at the receiver are structured so that they perform inverse operations. Non-coherent modulation methods do not require a receiver reference clock signal that is phase synchronized with the sender carrier wave. In this case, modulation symbols (rather than bits, characters, or data packets) are asynchronously transferred. The opposite is coherent modulation.

List of common digital modulation techniques The most common digital modulation techniques are: 1. Phase-shift keying (PSK): • Binary PSK (BPSK), using M=2 symbols

• Quadrature PSK (QPSK), using M=4 symbols • 8PSK, using M=8 symbols

• 16PSK, using M=16 symbols • Differential PSK (DPSK)

• Differential QPSK (DQPSK) • Offset QPSK (OQPSK) • fi/4-QPSK

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2. Frequency-shift keying (FSK): • Audio frequency-shift keying (AFSK)

• Multi-frequency shift keying (M-ary FSK or MFSK) • Dual-tone multi-frequency (DTMF)

3. Amplitude-shift keying (ASK)

4. On-off keying (OOK), the most common ASK form • M-ary vestigial sideband modulation, for example 8VSB

5. Quadrature amplitude modulation (QAM) - a combination of PSK and ASK: • Polar modulation like QAM a combination of PSK and ASK. 6. Continuous phase modulation (CPM) methods: • Minimum-shift keying (MSK)

• Gaussian minimum-shift keying (GMSK)

• Continuous-phase frequency-shift keying (CPFSK) 7. Orthogonal frequency-division multiplexing (OFDM) modulation: • discrete multitone (DMT) - including adaptive modulation and bit-loading. 8. Wavelet modulation 9. Trellis coded modulation (TCM), also known as trellis modulation Engineering Knowledge Test


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Page: 12 10. Spread-spectrum techniques: • Direct-sequence spread spectrum (DSSS)

• Chirp spread spectrum (CSS) according to IEEE 802.15.4a CSS uses pseudostochastic coding • Frequency-hopping spread spectrum (FHSS) applies a special scheme for channel release • SIM31 (SIM) New digital Mode SIM31 SIM63 tks SWL Tunisian MSK and GMSK are particular cases of continuous phase modulation. Indeed, MSK is a particular case of the sub-family of CPM known as continuous-phase frequency-shift keying (CPFSK) which is defined by a rectangular frequency pulse (i.e. a linearly increasing phase pulse) of one symbol-time duration (total response signaling).

Pulse modulation methods Pulse modulation schemes aim at transferring a narrowband analog signal over an analog baseband channel as a two-level signal by modulating a pulse wave. Some pulse modulation schemes also allow the narrowband analog signal to be transferred as a digital signal (i.e. as a quantized discrete-time signal) with a fixed bit rate, which can be transferred over an underlying digital transmission system, for example some line code. These are not modulation schemes in the conventional sense since they are not channel coding schemes, but should be considered as source coding schemes, and in some cases analog-to-digital conversion techniques. 1. Analog-over-analog methods: • Pulse-amplitude modulation (PAM)

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• Pulse-width modulation (PWM) AND Pulse-depth modulation (PDM) • Pulse-position modulation (PPM) 2. Analog-over-digital methods: • Pulse-code modulation (PCM

– Differential PCM (DPCM) – Adaptive DPCM (ADPCM)

• Delta modulation (DM or -modulation) q • Delta-sigma modulation ( )

• Continuously variable slope delta modulation (CVSDM), also called Adaptive-delta modulation (ADM) • Pulse-density modulation (PDM)

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TDMA: Time division multiple access

Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, combatnet radio systems, and PON networks for upstream traffic from premises to the operator. For usage of Dynamic TDMA packet mode communication, see below.



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TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.

TDMA characteristics • Shares single carrier frequency with multiple users

• Non-continuous transmission makes handoff simpler

• Slots can be assigned on demand in dynamic TDMA

• Less stringent power control than CDMA due to reduced intra cell interference • Higher synchronization overhead than CDMA

• Advanced equalization may be necessary for high data rates if the channel is ”frequency selective” and creates Intersymbol interference • Cell breathing (borrowing resources from adjacent cells) is more complicated than in CDMA • Frequency/slot allocation complexity

• Pulsating power envelope: Interference with other devices

TDMA in mobile phone systems 2G systems

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Most 2G cellular systems, with the notable exception of IS-95, are based on TDMA. GSM, DAMPS, PDC, iDEN, and PHS are examples of TDMA cellular systems. GSM combines TDMA with Frequency Hopping and wideband transmission to minimize common types of interference. In the GSM system, the synchronization of the mobile phones is achieved by sending timing advance commands from the base station which instructs the mobile phone to transmit earlier and by how much. This compensates for the propagation delay resulting from the light speed velocity of radio waves. The mobile phone is not allowed to transmit for its entire time slot, but there is a guard interval at the end of each time slot. As the transmission moves into the guard period, the mobile network adjusts the timing advance to synchronize the transmission. Initial synchronization of a phone requires even more care. Before a mobile transmits there is no way to actually know the offset required. For this reason, an entire time slot has to be dedicated to mobiles attempting to contact the network; this is known as the random-access channel (RACH) in GSM. The mobile attempts to broadcast at the beginning of the time slot, as received from the network. If the mobile is located next to the base station, there will be no time delay and this will succeed. If, however, the mobile phone is at just less than 35 km from the base station, the time delay will mean the mobile’s broadcast arrives at the very end of the time slot. In that case, the mobile will be instructed to broadcast its messages starting nearly a whole time slot earlier than would be expected otherwise. Finally, if the mobile is beyond the 35 km cell range in GSM, then the RACH will arrive in a neighbouring time slot and be ignored. It is this feature, rather than limitations of power, that limits the range of a GSM cell to 35 km when no special extension techniques are used. By changing the synchronization between the uplink and downlink at the base station, however, this limitation can be overcome. 3G systems Although most major 3G systems are primarily based upon CDMA, time division duplexing (TDD), packet scheduling (dynamic TDMA) and packet oriented multiple access schemes are available in 3G form, combined with CDMA to take advantage of the benefits of both technologies. Engineering Knowledge Test


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While the most popular form of the UMTS 3G system uses CDMA and frequency division duplexing (FDD) instead of TDMA, TDMA is combined with CDMA and Time Division Duplexing in two standard UMTS UTRA

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FDMA: Frequency-division multiple access

Frequency Division Multiple Access or FDMA is a channel access method used in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, or channels. It is particularly commonplace in satellite communication. FDMA, like other Multiple Access systems, coordinates access between multiple users. Alternatives include TDMA, CDMA, or SDMA. These protocols are utilized differently, at different levels of the theoretical OSI model. Disadvantage: Crosstalk may cause interference among frequencies and disrupt the transmission. • In FDMA all users share the satellite transponder or frequency channel simultaneously but each user transmits at single frequency. • FDMA can be used with both analog and digital signal.

• FDMA requires high-performing filters in the radio hardware, in contrast to TDMA and CDMA. • FDMA is not vulnerable to the timing problems that TDMA has. Since a predetermined frequency band is available for the entire period of communication, stream data (a continuous flow of data that may not be packetized) can easily be used with FDMA. • Due to the frequency filtering, FDMA is not sensitive to near-far problem which is pronounced for CDMA.

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• Each user transmits and receives at different frequencies as each user gets a unique frequency slots. FDMA is distinct from frequency division duplexing (FDD). While FDMA allows multiple users simultaneous access to a transmission system, FDD refers to how the radio channel is shared between the uplink and downlink (for instance, the traffic going back and forth between a mobile-phone and a mobile phone base station). Frequency-division multiplexing (FDM) is also distinct from FDMA. FDM is a physical layer technique that combines and transmits lowbandwidth channels through a high-bandwidth channel. FDMA, on the other hand, is an access method in the data link layer. FDMA also supports demand assignment in addition to fixed assignment. Demand assignment allows all users apparently continuous access of the radio spectrum by assigning carrier frequencies on a temporary basis using a statistical assignment process. The first FDMA demand-assignment system for satellite was developed by COMSAT for use on the Intelsat series IVA and V satellites. There are two main techniques: • Multi-channel per-carrier (MCPC) • Single-channel per-carrier (SCPC)

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CDMA: Code division multiple access

• Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. • CDMA is an example of multiple access, which is where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth). To permit this without undue interference between the users, CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code). Engineering Knowledge Test


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• CDMA is used as the access method in many mobile phone standards such as cdmaOne, CDMA2000 (the 3G evolution of cdmaOne), and WCDMA (the 3G standard used by GSM carriers), which are often referred to as simply CDMA.

Steps in CDMA modulation CDMA is a spread-spectrum multiple access technique. A spread spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. A spreading code is a pseudo-random code that has a narrow ambiguity function, unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is combined via bitwise XOR (exclusive OR) with the faster code. The figure shows how a spread spectrum signal is generated. The data signal with pulse duration of Tb (symbol period) is XOR’ed with the code signal with pulse duration of Tc (chip period). (Note: bandwidth is proportional to 1/T, where T = bit time.) Therefore, the bandwidth of the data signal is 1/Tb and the bandwidth of the spread spectrum signal is 1/Tc . Since Tc is much smaller than Tb , the bandwidth of the spread spectrum signal is much larger than the bandwidth of the original signal. The ratio Tb /Tc is called the spreading factor or processing gain and determines to a certain extent the upper limit of the total number of users supported simultaneously by a base station.

shop.ssb cra ck.com Each user in a CDMA system uses a different code to modulate their signal. Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. The best performance will occur when there is good separation between the signal of a desired user and the signals of other users. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. If the signal matches the desired user’s code then the correlation function will be high and the system can extract that signal. If the desired user’s code has nothing in common with the signal the correlation should be as close to zero as possible (thus eliminating the signal); this is referred to as cross-correlation. If the code is correlated with the signal at any time offset other than zero, the correlation should be as close to zero as possible. This is referred to as auto-correlation and is used to reject multi-path interference. An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can communicate. In general, CDMA belongs to two basic categories: synchronous (orthogonal codes) and asynchronous (pseudorandom codes).

11

Code division multiplexing (synchronous CDMA)

The digital modulation method is analogous to those used in simple radio transceivers. In the analog case, a low frequency data signal is time multiplied with a high frequency pure sine wave carrier, and transmitted. This is effectively a frequency convolution (Weiner-Kinchin Engineering Knowledge Test


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Theorem) of the two signals, resulting in a carrier with narrow sidebands. In the digital case, the sinusoidal carrier is replaced by Walsh functions. These are binary square waves that form a complete orthonormal set. The data signal is also binary and the time multiplication is achieved with a simple XOR function. This is usually a Gilbert cell mixer in the circuitry. Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. For example, binary string 1011 is represented by the vector (1, 0, 1, 1). Vectors can be multiplied by taking their dot product, by summing the products of their respective components (for example, if u = (a, b) and v = (c, d), then their dot product uÂ v = ac + bd). If the dot product is zero, the two vectors are said to be orthogonal to each other. Some properties of the dot product aid understanding of how W-CDMA works. If vectors a and b are orthogonal, then a·b = 0 and: a · (a + b) = ÎaÎ2

since

a · a + a · b = ÎaÎ2 + 0

a · (≠a + b) = ≠ÎaÎ2

since

≠ a · a + a · b = ≠ÎaÎ2 + 0

b · (a + b) = ÎbÎ2

since

b · a + b · b = 0 + ÎbÎ2

b · (a ≠ b) = ≠ÎbÎ2

since

b · a ≠ b · b = 0 ≠ ÎbÎ2

Each user in synchronous CDMA uses a code orthogonal to the others’ codes to modulate their signal. An example of four mutually orthogonal digital signals is shown in the figure. Orthogonal codes have a cross-correlation equal to zero; in other words, they do not interfere with each other. In the case of IS-95 64 bit Walsh codes are used to encode the signal to separate different users. Since each of the 64 Walsh codes are orthogonal to one another, the signals are channelized into 64 orthogonal signals. The following example demonstrates how each user’s signal can be encoded and decoded.

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Fundamentals of mobile communication

Evolution of Mobile Radio Communications The first wireline telephone system was introduced in the year 1877. Mobile communication systems as early as 1934 were based on Amplitude Modulation (AM) schemes and only certain public organizations maintained such systems. With the demand for newer and better mobile radio communication systems during the World War II and the development of Frequency Modulation (FM) technique by Edwin Armstrong, the mobile radio communication systems began to witness many new changes. Mobile telephone was introduced in the year 1946. However, during its initial three and a half decades it found very less market penetration owing to high costs and numerous technological drawbacks. But with the development of the cellular concept in the 1960s at the Bell Laboratories, mobile communications began to be a promising field of expanse which could serve wider populations. Initially, mobile communication was restricted to certain official users and the cellular concept was never even dreamt of being made commercially available. Moreover, even the growth in the cellular networks was very slow. However, with the development of newer and better technologies starting from the 1970s and with the mobile users now connected to the Public Switched Telephone Network (PSTN), there has been an astronomical growth in the cellular radio and the personal communication systems. Advanced Mobile Phone System (AMPS) was the first U.S. cellular telephone system and it was deployed in 1983. Wireless services have since then been experiencing a 50per year growth rate. The number of cellular telephone users grew from 25000 in 1984 to around 3 billion in the year 2007 and the demand rate is increasing day by day.



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shop.ssb cra ck.com Present Day Mobile Communication Since the time of wireless telegraphy, radio communication has been used extensively. Our society has been looking for acquiring mobility in communication since then. Initially the mobile communication was limited between one pair of users on single channel pair. The range of mobility was defined by the transmitter power, type of antenna used and the frequency of operation. With the increase in the number of users, accommodating them within the limited available frequency spectrum became a major problem. To resolve this problem, the concept of cellular communication was evolved. The present day cellular communication uses a basic unit called cell. Each cell consists of small hexagonal area with a base station located at the center of the cell which communicates with the user. To accommodate multiple users Time Division multiple Access (TDMA), Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA) and their hybrids are used. Numerous mobile radio standards have been deployed at various places such as AMPS, PACS,GSM, NTT, PHS and IS-95, each utilizing different set of frequencies and allocating different number of users and channels.

Radio Transmission Techniques • Simplex System: Simplex systems utilize simplex channels i.e., the communication is unidirectional. The first user can communicate with the second user. However, the second user cannot communicate with the first user. One example of such a system is a pager. • Half Duplex System: Half duplex radio systems that use half duplex radio channels allow for non-simultaneous bidirectional communication. The first user can communicate with the second user but the second user can communicate to the first user only after the first user has finished his conversation. At a time, the user can only transmit or receive



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information. A walkie-talkie is an example of a half duplex system which uses ’push to talk’ and ’release to listen’ type of switches • Full Duplex System: Full duplex systems allow two way simultaneous communications. Both the users can communicate to each other simultaneously. This can be done by providing two simultaneous but separate channels to both the users. This is possible by one of the two following methods. – Frequency Division Duplexing (FDD): FDD supports two-way radio communication by using two distinct radio channels. One frequency channel is transmitted downstream from the BS to the MS (forward channel). – Time Division Duplexing (TDD): TDD uses a single frequency band to transmit signals in both the downstream and upstream directions. TDD operates by toggling transmission directions over a time interval. This toggling takes place very rapidly and is imperceptible to the user.

How a Mobile Call is Actually Made? In order to know how a mobile call is made, we should first look into the basics of cellular concept and main operational channels involved in making a call. These are given below. Cellular Concept Cellular telephone systems must accommodate a large number of users over a large geographic area with limited frequency spectrum, i.e., with limited number of channels. If a single transmitter/ receiver is used with only a single base station, then sufficient amount of power may not be present at a huge distance from the BS. For a large geographic coverage area, a high powered transmitter therefore has to be used. But a high power radio transmitter causes harm to environment. Mobile communication thus calls for replacing the high power transmitters by low power transmitters by dividing the coverage area into small segments, called cells. Each cell uses a certain number of the available channels and a group of adjacent cells together use all the available channels. Such a group is called a cluster. This cluster can repeat itself and hence the same set of channels can be used again and again. Each cell has a low power transmitter with a coverage area equal to the area of the cell. This technique of substituting a single high powered transmitter by several low powered transmitters to support many users is the backbone of the cellular concept.

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Operational Channels In each cell, there are four types of channels that take active part during a mobile call. These are: • Forward Voice Channel (FVC): This channel is used for the voice transmission from the BS to the MS. • Reverse Voice Channel (RVC): This is used for the voice transmission from the MS to the BS. • Forward Control Channel (FCC): Control channels are generally used for controlling the activity of the call, i.e., they are used for setting up calls and to divert the call to unused voice channels. Hence these are also called setup channels. These channels transmit and receive call initiation and service request messages. The FCC is used for control signaling purpose from the BS to MS. • Reverse Control Channel (RCC): This is used for the call control purpose from the MS to the BS. Control channels are usually monitored by mobiles



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Page: 19 Making a Call

When a mobile is idle, i.e., it is not experiencing the process of a call, then it searches all the FCCs to determine the one with the highest signal strength. The mobile then monitors this particular FCC. However, when the signal strength falls below a particular threshold that is insufficient for a call to take place, the mobile again searches all the FCCs for the one with the highest signal strength. For a particular country or continent, the control channels will be the same. So all mobiles in that country or continent will search among the same set of control channels. However, when a mobile moves to a different country or continent, then the control channels for that particular location will be different and hence the mobile will not work. Each mobile has a mobile identification number (MIN). When a user wants to make a call, he sends a call request to the MSC on the reverse control channel. He also sends the MIN of the person to whom the call has to be made. The MSC then sends this MIN to all the base stations. The base station transmits this MIN and all the mobiles within the coverage area of that base station receive the MIN and match it with their own. If the MIN matches with a particular MS, that mobile sends an acknowledgment to the BS. The BS then informs the MSC that the mobile is within its coverage area. The MSC then instructs the base station to access specific unused voice channel pair. The base station then sends a message to the mobile to move to the particular channels and it also sends a signal to the mobile for ringing. In order to maintain the quality of the call, the MSC adjusts the transmitted power of the mobile which is usually expressed in dB or dBm. When a mobile moves from the coverage area of one base station to the coverage area of another base station i.e., from one cell to another cell, then the signal strength of the initial base station may not be sufficient to continue the call in progress. So the call has to be transferred to the other base station. This is called handoff. In such cases, in order to maintain the call, the MSC transfers the call to one of the unused voice channels of the new base station or it transfers the control of the current voice channels to the new base station.

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Fundamentals of optical fibre communication

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks in the developed world. Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Researchers at Bell Labs have reached internet speeds of over 100 petabits per second using fiber-optic communication. The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal.

Technology Modern fiber-optic communication systems generally include an optical transmitter to convert an electrical signal into an optical signal to send into the optical fiber, a cable containing bundles of multiple optical fibers that is routed through underground conduits and buildings, multiple kinds of amplifiers, and an optical receiver to recover the signal as an electrical signal. The information transmitted is typically digital information generated by computers, telephone systems, and cable television companies. Transmitters The most commonly used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and laser diodes. The difference between LEDs and laser diodes is that LEDs



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produce incoherent light, while laser diodes produce coherent light. For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient, and reliable, while operating in an optimal wavelength range, and directly modulated at high frequencies. A transceiver is a device combining a transmitter and a receiver in a single housing (see picture on right). Receivers The main component of an optical receiver is a photodetector, which converts light into electricity using the photoelectric effect. The primary photodetectors for telecommunications are made from Indium gallium arsenide The photodetector is typically a semiconductor-based photodiode. Several types of photodiodes include p-n photodiodes, p-i-n photodiodes, and avalanche photodiodes. Metal-semiconductor-metal (MSM) photodetectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers. Optical-electrical converters are typically coupled with a transimpedance amplifier and a limiting amplifier to produce a digital signal in the electrical domain from the incoming optical signal, which may be attenuated and distorted while passing through the channel. Further signal processing such as clock recovery from data (CDR) performed by a phase-locked loop may also be applied before the data is passed on. Fiber cable types An optical fiber cable consists of a core, cladding, and a buffer (a protective outer coating), in which the cladding guides the light along the core by using the method of total internal reflection. The core and the cladding (which has a lower-refractive-index) are usually made of high-quality silica glass, although they can both be made of plastic as well. Connecting two optical fibers is done by fusion splicing or mechanical splicing and requires special skills and interconnection technology due to the microscopic precision required to align the fiber cores. Two main types of optical fiber used in optic communications include multi-mode optical fibers and single-mode optical fibers. A multi-mode optical fiber has a larger core (â 50 micrometers), allowing less precise, cheaper transmitters and receivers to connect to it as well as cheaper connectors. However, a multi-mode fiber introduces multimode distortion, which often limits the bandwidth and length of the link. Furthermore, because of its higher dopant content, multi-mode fibers are usually expensive and exhibit higher attenuation. The core of a single-mode fiber is smaller (¡10 micrometers) and requires more expensive components and interconnection methods, but allows much longer, higher-performance links

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'

Communication'System'MCQs'

Communication*System:*MCQs* ' 1.''Modulation'is'primarily'accomplished'to' (a)' produce'sidebands' (b)' mix'two'waves'of'different' frequencies' (c)' transmit'audioDfrequency'signals' (d)' improve'transmission'efficiency' over'long'distance' ' 2.''In'AM'wave' (a)' RF'and'AF'waves'are'sent' (b)' carrier'wave'magnitude'varies'with' alternately' AF'signal' (c)' RF'signal'should'be'an'even' (d)' RF'signal'should'be'an'even'multiple' multiple'of'AF'signal' of'AF'signal' ' 3.''The'disadvantage'of'low'level'modulation'system'is' (a)' High'modulating'power' (b)' Linear'device'is'to'be'used'after' modulation' (c)' amplifier'of'large'power'capacity' (d)' amplifier'of'large'bandwidth'is'to' is'to'be'used'after'modulation' used'after'modulation' ' 4.''Limitation'of'AM'modulation'is/are' (a)' Noisy'reception' (b)' Low'transmission'efficiency'and'small' operating'range' (c)' Poor'audio'quality' (d)' All'of'the'above''' ' 5.''In'an'AM'system,'for'satisfactory'operation,'carrier'frequency'must'be'n'times'the' bandwidth'of'message'signal.'What'is'the'value'of'n'?' (a)' >2'''''''''''''' (b)' >5' (c)' >10' (d)' >50' ' 6.''In'a'100%'amplitude'modulated'signal,'if'the'total'transmitted'power'is'P,'then' carrier'power'will'be' (a)' 2/3'P' (b)' 1/2'P' (c)' 1/3'P' (d)' 1/4'P' ' 07.''Which'one'of'the'following'is'considered'as'an'AM'signal?' ' (a)' Binary'phase'shift'keying'(BPSK)' (b)' Differential'phase'shift'keying'(DPSK)' (c)' Differential'encoded'PSK' (d)' Quadrature'PSK'


' 08.''A'modulator'is'a'device'to' (a)' Separate'two'frequencies' (c)' Extract'information'from'the' carrier'

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(b)' Impress'the'information'on'to'a'radio' frequency'carrier' (d)' Amplify'the'audio'frequency'signal'

' '09.'The'collector'modulation'is'commonly'used'because'of'its'following'advantage(s)' (a)' Good'linearity'and'high'collector' (b)' Low'modulating'power'requirement' circuit'efficiency' (c)' Hundred'percent'modulation'can' (d)' All'of'the'above' be'achieved' ' ' ' 10.''Which'of'the'following'modulated'signals'can'be'detected'by'an'envelope'detector?' (a)' DSBDsuppressed'carrier' (b)' DSBDfull'carrier' (c)' Frequency'modulated'signal' (d)' SSBDsupported'carrier' ' 11.'One'of'the'advantage'of'base'modulation'over'collector'modulation'of'a'transistor' Class'C'amplifier'is' (a)' the'lower'modulating'power' (b)' higher'power'output'per'transistors' required' (c)' better'efficiency' (d)' better'linearity' ' ' 12.'The'demodulation'of'a'delta'modulated'signal'is'achieved'by:' (a)' integration' (b)' differentiation' (c)' sampling' (d)' band'pass'filtering' ' 13.'“Slope'overload”'occurs'in'delta'modulation'when'the'' (a)' frequency'of'the'clock'pulses'is' (b)' rate'of''change'of'analog'waveform'is' too'low' too'large' (c)' step'size'is'too'small' (d)' analog'signal'varies'very'slowly'with' time' ' ' '


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14.''The'most'useful'modulation'technique'for'high'fidelity'audio'broadcasting'on'radio' in'current'practices'is' (a)' amplitude'modulation' (b)' frequency'modulation' (c)' pulse'amplitude'modulation' (d)' pulse'code'modulation' ' 15.''In'frequency'modulation' (a)' the'frequency'of'the'carrier' (b)' the'amplitude'of'carrier'remains' remains'constant' constant' ' (c)' the'amplitude'of'the'carrier'wave' (d)' the'frequency'of'the'signal'is'made' is'varied' equal'to'the'carrier'frequency' ' 16.'Consider'the'following'statements'about'FM:' '' 1.! Modulation'index'determines'the'number'of'significant'sideband'components.' 2.! Theoretical'bandwidth'is'infinite.' 3.! Carrier'suppression'is'not'possible.' 4.! Sidebands'are'not'symmetric'about'carrier.' Which'of'the'above'statements'is/are'correct?' (a)' 1,2,3'and'4' (b)' 1'and'2'only' (c)' 3'and'4'only' (d)' 3'only' ' 17.'Which'one'of'the'following'factors'is'limited'in'case'of'F.M.?' (a)' Maximum'frequency'deviation' (b)' Maximum'permissible'modulation' index' (c)' Signal'to'noise'voltage'ration' (d)' Minimum'permissible'modulation' index' ' 18.'Which'of'the'following'are'the'advantages'of'FM'broadcasting'over'AM' broadcasting?' 1.! Better'S/N'radio' 2.! Not'subject'to'signal'fading' 3.! Power'efficiency'is'superior' 4.! Demodulation'is'simpler' Select'the'correct'answer'from'the'code'given'below:' (a)' 1'and'2' (b)' 1,2'and'4' (c)' 2,3'and'4' (d)' 1'and'3'


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' 19.'Why'does'an'FM'radio'station'perform'better'than'an'AM'station'radiating'the'same' total'power?' (a)' FM'is'immune'to'noise' (b)' AM'has'only'two'sidebands'while'FM' has'more' (c)' FM'uses'large'bandwidth'for'large' (d)' Capture'effect'appears'in'FM' modulation'depth' ' ' 20.'In'phase'modulation,'phase'deviation'is'proportional'to'' (a)' carrier'amplitude' (b)' carrier'phase' (c)' message'signal' (d)' message'signal'frequencies' ' 21.'Which'one'of'the'following'in'an'indirect'way'of'generating'FM?' (a)' Reactance'FET'modulator' (b)' Varactor'diode'modulator' (c)' Armstrong'modulator' (d)' Reactance'tube'modulator' ' 22.'The'most'common'detector'used'in'an'AM'radio'broadcast'receiver'is' (a)' envelope'detector' (b)' coherent'detector' (c)' discriminator' (d)' ratio'detector'' ' 23.'What'is'the'automatic'frequency'control'voltage'of'the'FM'transmitter'VCO?' (a)' DC'voltage' (b)' Sine'wave'voltage' (c)' Square'wave'voltage' (d)' Ramp'voltage' ' 24.'The'main'advantage'of'preDemphasis'circuit'in'FM'transmitter'is' (a)' to'increase'the'carrier'power' (b)' to'improve'the'signal'to'noise'ratio'at' low'audio'frequencies' (c)' to'increase'the'bandwidth'of'side' (d)' to'improve'the'signal'to'noise'ratio'at' band' high'audio'frequencies' 25.'PLL'demodulators'are'now'used'in'commercial'receivers'because'of'which'of'the' following:' 1.! PLL'demodulators'do'not'exhibit'threshold'in'S/N'performance'' 2.! No'requirement'of'preDemphasis'and'deDemphasis' 3.! Cheap'PLL'ICs'are'available' Select'the'correct'answer'using'the'code'given'below:' (a)' 1'and'2'only' (b)' 2'and'3'only' (c)' 1'and'3'only' (d)' 1,'2'and'3' '


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26.''MSK'(Minimum'Shift'Keying)'is'an'orthogonal'FSK'scheme'that'gets'its'name'from' the'fact'that' (a)' the'phase'shift'is'minimum' (b)' the'error'probability'is'minimum' (c)' the'transmission'power'required' (d)' the'transmission'bandwidth'required' is'minimum' is'minimum' ' 27.''Which'one'of'the'following'is'a'disadvantage'of'digital'transmission'as'compared'to' analog'transmission?' (a)' Digital'signals'cannot'be' (b)' Digital'transmission'is'less'immune'to' multiplexed'efficiently' channel'noise' (c)' Digital'signals'needs'to'be'coded' (d)' Digital'transmission'needs'more' before'transmission' bandwidth' ' 28.''Which'one'of'the'following'pulse'communications'systems'is'digital?' (a)' PAM' (b)' PCM' (c)' PPM' (d)' PWM' ' 29.'PPM'signal'is' (a)' differentiation'of'PWM' (b)' integration'PWM' (c)' differentiation'of'PAM' (d)' not'related'to'PWM'or'PAM' ' 30.''In'digital'communication'system,'the'data'transmission'rate'is'specified'in' (a)' MHz' (b)' bits/second' (c)' bytes/seconds' (d)' bauds' ' 31.'In'differential'PCM,'each'word'indicates' (a)' difference'between'a'sample' (b)' difference'in'amplitude'between'a' amplitude'and'a'reference'signal' sample'and'the'previous'sample.' (c)' addition'of'a'sample'amplitude' (d)' addition'of'amplitude'of'a'sample' and'a'reference'signal' and'the'previous'sample' ' 32.'Consider'the'following'statements:' The'thermal'noise'power'generated'by'a'resistor'is'proportional'to'' 1.! the'value'of'the'resistor' 2.! the'absolute'temperature' 3.! the'bandwidth'over'which'it'is'measured' 4.! the'Boltzmann’s'constant'


'


which'of'the'above'statement'is/are'correct?' (a)' 1,2'and'3' (b)' 2'only' (c)' 2'and'3'only' (d)' 2,3'and'4'' ' 33.''Quantizing'noise'occurs'in' (a)' Pulse'width'modulation' (b)' Frequency'division'multiplexing' (c)' Pulse'code'modulation' (d)' Time'division'multiplexing' ' 34.'For'which'of'the'following'systems,'the'signal'to'noise'ratio'is'the'highest?' (a)' PAM' (b)' PWM' (c)' PPM' (d)' PAM'and'PWM' ' 35.''The'most'noise'immune'system'is' (a)' SSB' (b)' PCM' (c)' PDM' (d)' PWM' ' ' 36.''Which'one'of'the'following'pairs'is'not'correctly'matched?' (a)' DSMDSC'modulation:'balanced' (b)' PCM:'PreDemphasis' modulator' (c)' FM:'Reactance'modulator' (d)' SSB'modulation:'Weaver’s'method' ' ' 37.''The'types'of'modulation'used'generally'in'TV'transmission'for'video'and'audio' signals,'respectively,'are' (a)' FM'and'AM' (b)' FM'and'FM' (c)' AM'and'AM' (d)' AM'and'FM' ' 38.''Consider'the'following'statements:' ' 1.! An'active'satellite'is'one'carrying'a'receiver,'a'transmitter'and'power'supplies' 2.! A'passive'satellite'is'simply'a'metallized'sphere'reflecting'radio'signals'back'to'the' earth' ' Which'of'the'statements'given'above'is/are'correct?' (a)' 1'only' (b)' 2'only' (c)' Both'1'and'2' (d)' Neither'1'nor'2' '


'


39.'What'is'the'reason'for'using'frequencies'of'the'order'of'few'GHz'in'satellite' communication?' (a)' Antenna'sizes'are'small'and' (b)' Helical'antennas'can'be'used'at'these' ionosphere'does'not'reflect' frequencies' frequencies' (c)' Frequencies'can'pass'through' (d)' Easy'availability'of'components'at' ionosphere'without'attenuation' these'frequencies' ' 40.''Which'one'of'the'following'is'correct?'In'satellite'communication'links,'generally,' (a)' the'uplink'carrier'frequencies'are' (b)' the'uplink'carrier'frequencies'are' greater'than'downlink'carrier' lesser'than'downlink'carrier' frequencies' frequencies' (c)' both'uplink'and'downlink'carrier' (d)' it'is'not'necessary'to'use'carrier'at'all' frequencies'are'same' ' 41.'Which'one'of'the'following'is'the'correct'statement?'If'the'value'of'a'resistor' creating'thermal'noise'is'doubled,'the'noise'generated'is' (a)' halved' (b)' doubled' (c)' unchanged' (d)' slightly'changed' ' 42.'Which'one'of'the'following'is'the'correct'statement?'If'the'channel'bandwidth'is' doubled,'the'S/N'ratio'becomes' (a)' double'of'the'former'S/N'ratio' (b)' double'of'the'former'S/N'ratio' (c)' half'of'the'former'S/N'ratio' (d)' None'of'the'above' ' 43.'Which'one'of'the'following'is'correct?' (a)' Coding'reduces'the'noise'in'the' (b)' Coding'reduces'the'noise'in'the'signal' signal' (c)' Coding'increases'the'information' (d)' Coding'increases'the'channel'band' rate' bandwidth' ' 44.'The'capacity'of'a'channel'is'given'by'the' (a)' number'of'digits'used'in'coding' (b)' volume'of'information'it'can'take' (c)' maximum'rate'of'information' (d)' bandwidth'required'for'information' transmitted' ' '


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45.''If'large'amount'of'information'is'to'be'transmitted'in'a'small'amount'of'time,'we' require' (a)' LowDfrequency'signals' (b)' Narrowband'signals' (c)' Wideband'signals' (d)' HighDfrequency'signals' ' ' 46.''Cavity'resonators'are'used'in' (a)' MF'band' (b)' HF'band' (c)' VHF'band' (d)' SHF'band' ' 47.'What'is'the'main'objective'of'trellis'coding?' (a)' To'narrow'the'bandwidth' (b)' To'simplify'modulation'' (c)' To'increase'the'data'rate' (d)' To'reduce'the'error'rate' ' 48.'Light'travels'along'the'optical'fibres'by'which'mechanism?' (a)' Refraction' (b)' Reflection' (c)' Scattering' (d)' Total'internal'reflection' ' 49.'A'single'mode'fibre'does'not'suffer'from'which'type'of'dispersion?' (a)' Waveguide'dispersion' (b)' Material'dispersion' (c)' Intermodal'dispersion' (d)' Polarization'mode'dispersion' ' 50.''Which'of'the'following'introduces'mode'partition'noise?' (a)' Coaxial'line' (b)' Waveguide' (c)' Fibre'transmission'line' (d)' Both'coaxial'line'and'waveguide' ' 51.''In'FDM'systems'used'for'telephone,'which'modulation'scheme'is'adopted?' (a)' AM' (b)' DSBDSC' (c)' SSBDSC' (d)' FM' ' 52.''Consider'the'following'statements:'If'the'maximum'range'of'a'radar'has'to'be' doubled,' (a)' the'peak'transmitted'power'may' (b)' the'antenna'diameter'may'be' be'increased'16'fold' doubled' ' (c)' the'sensitivity'of'the'receiver'may' (d)' the'transmitted'pulse'width'may'be' be'doubled' doubled' '


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' 53.''Telemetry'processes'the'information'from'a'remote'location'by'means'of'' (a)' mechanical'means' (b)' electrical'means' (c)' CRO' (d)' All'of'the'above' ' 54.''The'most'commonly'used'transmission'channels'are' (a)' cables' (b)' radio'links' (c)' pneumatic' (d)' both'(a)'and'(b)' ' ' 55.'The'position'telemetering'system'using'synchros'is' (a)' a'pulse'telemetering'system' (b)' a'rf'telemetering'system' (c)' a'dc'telemetering'system' (d)' an'ac'telemetering'system' ' 56.''Which'one'of'the'following'telemetering'system'is'a'digital'system?' (a)' Pulse'code'modulation'(PCM)' (b)' Position'telemetering'system'using' system' synchros' (c)' DC'voltage'telemetering'system' (d)' Pulse'duration'modulation'(PDM)' ' ' 57.''What'are'the'three'steps'in'generating'PCM'in'the'correct'sequence?' (a)' Sampling,'quantizing'and' (b)' Encoding,'sampling'and'quantizing' encoding' (c)' Sampling'encoding'and'quantizing' (d)' Quantizing,'sampling'and'encoding' ' 58.''Which'one'of'the'following'modulation'techniques'is'the'most'efficient'for'pulse' telemetry?' (a)' PAM' (b)' PCM' (c)' PDM' (d)' PPM' ' 59.'When'system'noise'is'large'and'signal'power'is'low'in'telemetry'system,'what'is'the' preferred'form'of'modulation?' (a)' PulseDwidth'modulation' (b)' PulseDamplitude'modulation' (c)' PulseDcode'modulation' (d)' PulseDposition'modulation' ' ' '


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60.'Which'signaling'scheme'is'most'affected'by'noise?' (a)' ASK' (b)' FSK' (c)' PSK' (d)' QAM' ' 61.''Which'one'of'the'following'modulation'technique'is'most'affected'by'noise?' (a)' ASK' (b)' PSK' (c)' FSK' (d)' MSK' ' 62.''Which'one'of'the'following'systems'offers'the'best'trade'off'between'bandwidth' and'S/N'ratio' (a)' PAM' (b)' PDM' (c)' PPM' (d)' PCM' ' 63.'Which'of'the'following'pulse'communication'system'is'inherently'immune'to'noise?' (a)' PPM' (b)' PCM' (c)' PWM' (d)' PAM' ' 64.''Compounding'is'used' (a)' to'overcome'quantisting''noise'in' (b)' in'PWM'receivers'to'reduce'impulse' PCM' noise' (c)' to'protect'small'signal'in'PC'from' (d)' none'of'the'above' quantisting'noise' ' 65.''PDM'is'generated'by'using' (a)' monostable'multivibrator' (b)' free'running'multivibrator' (c)' bistable'multivibrator' (d)' JK'flip'flop' ' 66.''If'large'amount'of'information'is'to'be'transmitted'in'a'small'amount'of'time,'we' require' (a)' lowDfrequency'signals' (b)' narrowband'signals' (c)' wideband'signals' (d)' highDfrequency'signals' ' ' 67.''In'comparison'to'PPM,'the'PDM'has'the'disadvantage'of'requiring'' (a)' more'samples'per'second' (b)' powerful'transmitter' (c)' pulses'of'larger'widths' (d)' none'of'the'above'' ' '


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68.''In'comparison'of'PPM,'which'of'the'following'statements'is/are'true'for'PDM?' (a)' The'pulse'amplitude'in'PDM' (b)' The'PDM'transmitter'should'be'able' remains'constant' to'handle'maximum'width'pulse' (c)' PDM'will'still'work'if' (d)' all'of'the'above' synchronization'between' transmitter'and'receiver'fails' ' 69.'PPM' (a)' needs'constant'transmitter'power' (b)' can'be'generated'from'PDM' output' (c)' depends'upon'transmitter' (d)' all'of'the'above' receiver'synchronization' ' ' 70.'Which'of'the'following'pulse'systems'needs'higher'bandwidth?' (a)' PPM' (b)' PAM' (c)' PDM' (d)' none'of'these' ' 71.''PCM' (a)' is'a'digital'system' (b)' is'inherently'most'noise'resistant' (c)' has'no'carrierDwave'equivalent' (d)' all'of'the'above' ' 72.''Which'of'the'following'pulse'modulations'are'digital?' 1.! PCM' 2.! Differential'PCM' 3.! PWM' Select'the'correct'answer'using'the'code'given'below:' (a)' 1'and'2'only' (b)' 2'and'3'only' (c)' 1'and'3'only' (d)' 1,2'and'3' ' 73.''Which'one'of'the'following'circuits'transmits'two'messages'simultaneously'in'one' direction?' (a)' Duplex' (b)' Diplex' (c)' Simplex' (d)' Quadruplex' ' 74.''A'PWM'signal'can'be'generated'by' (a)' an'astable'multivibrator'' (b)' a'monostable'multivibrator' (c)' integrating'a'PPM'signal' (d)' differentiating'a'PPM'signal' '


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75.''In'PCM' (a)' noise'is'removed'by'regenerating' (b)' noiseDfree'signal'is'transmitted'at' pulses'at'each'repeater'station' each'repeater'station' (c)' only'noise'on'the'link'between' (d)' all'of'the'above' repeater'stations'is'to'be' ' considered' ' 76.''Which'one'of'the'following'statement'is'correct?' Quantising'noise'is'produced'in' (a)' all'pulse'modulation'systems' (b)' PCM' (c)' All'modulation'systems' (d)' PDM' ' 77.''The'noise'is'reduced'by' (a)' using'redundancy' (b)' increasing'the'transmitted'power' (c)' reducing'the'signaling'rate' (d)' all'of'the'above' ' 78.''Which'one'of'the'following'multiplexing'technique'involves'signal'composed'of'light' beams?' (a)' CDM' (b)' FDM' (c)' TDM' (d)' WDM' ' 79.''In'case'of'data'transmission,'which'one'of'the'following'systems'will'give'the' maximum'probability'error?' (a)' ASK' (b)' FSK' (c)' PSK' (d)' DPSK' ' 80.''A'handshake'signal'in'a'data'transfer'is'transmitted' (a)' along'with'the'data'bits' (b)' before'the'data'transfer' (c)' after'the'data'transfer' (d)' either'along'with'the'data'bits'or' after'the'data'transfer'' ' 81.''Which'one'of'the'following'transmission'systems'for'telemetry'has'largest' bandwidth?' (a)' FM/FM'radio'transmission'system' (b)' CoDaxial'copper'cables'transmission' system' (c)' FiberDoptic'data'transmission' (d)' SynchroDposition'repeater'system' system' '


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82.'In'an'optical'fibre,'the'light'beam'propagates'due'to'which'one'of'the'following?' (a)' Simple'reflection'of'light'at'a' (b)' Refraction'of'light'in'the'medium' boundary'between'two'media' (c)' Total'internal'reflection'at'the' (d)' Scattering'of'light'in'the'medium' boundary'of'the'fibre' ' ' 83.'Losses'in'optical'fibres'can'be'caused'by'which'of'the'following?' ' 1.! Impurities' 2.! Micro'bending' 3.! Stepped'index'operation' Select'the'correct'answer'using'the'code'given'below:' (a)' 1'and'3' (b)' 2'and'3' (c)' 1'and'2' (d)' 3'only' ' 84.''Dispersion'in'an'optical'fiber'used'in'a'communication'link'is'of'which'type?' (a)' Angular'dispersion' (b)' Modal'dispersion' (c)' Chromatic'dispersion' (d)' Dispersion'arising'due'to'structural' irregularities'in'the'fiber' ' * *


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Microwave Engineering

Contents 1 What is a Waveguide 1.1 Principle of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Uses of Waveguide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 2 2

2 Klystron 2.1 How it works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 3

1

What is a Waveguide

A waveguide is a structure that guides waves, such as electromagnetic waves or sound waves. For example you want to propagate a signal at a perticular house, if you relay that signal in open space without using any guide, other may hear your signal as your singal will spread in all direction. To avoid this problem you can use a wave guide to propagate your in the direction of that perticular house. • There are different types of waveguides for each type of wave. The original and most common meaning is a hollow conductive metal pipe used to carry high frequency radio waves, particularly microwaves.

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• The frequency of the transmitted wave also dictates the shape of a waveguide:

Figure 1: One of the commercially available waveguides in market.

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• An optical fiber guiding high-frequency light will not guide microwaves of a much lower frequency. As a rule of thumb, the width of a waveguide needs to be of the same order of magnitude as the wavelength of the guided wave.

1.1

Principle of operation

• Waves propagate in all directions in open space as spherical waves.

• The power of the wave falls with the distance R from the source as the square of the distance(inverse square law). • A waveguide confines the wave to propagate in one dimension, so that, under ideal conditions, the wave loses no power while propagating. • The conductors generally used in waveguides have small skin depth and hence large surface resistance. • Due to total reflection at the walls, waves are confined to the interior of a waveguide. The propagation inside the waveguide, hence, can be described approximately as a ”zigzag” between the walls. This description is exact for electromagnetic waves in a hollow metal tube with a rectangular or circular cross-section.

1.2

Uses of Waveguide

The uses of waveguides for transmitting signals were known even before the term was coined. The phenomenon of sound waves guided through a taut wire have been known for a long time, as well as sound through a hollow pipe such as a cave or medical stethoscope. Other uses of waveguides are in transmitting power between the components of a system such as radio, radar or optical devices. Waveguides are the fundamental principle of guided wave testing (GWT), one of the many methods of non-destructive evaluation.

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• Optical fibers transmit light and signals for long distances and with a high signal rate.

• In a microwave oven a waveguide transfers power from the magnetron, where waves are formed, to the cooking chamber. • In a radar, a waveguide transfers radio frequency energy to and from the antenna, where the impedance needs to be matched for efficient power transmission (see below). • A waveguide called a stripline can be created on a printed circuit board, and is used to transmit microwave signals on the board. This type of waveguide is very cheap to manufacture and has small dimensions which fit inside printed circuit boards. • Waveguides are used in scientific instruments to measure optical, acoustic and elastic properties of materials and objects. • The waveguide can be put in contact with the specimen (as in a medical ultrasonography), in which case the waveguide ensures that the power of the testing wave is conserved, or the specimen may be put inside the waveguide (as in a dielectric constant measurement), so that smaller objects can be tested and the accuracy is better.



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Klystron • A klystron is a specialized linear-beam vacuum tube which is used as an amplifier for high radio frequencies, from UHF up into the microwave range. • Low-power klystrons are used as oscillators in terrestrial microwave relay communications links, • High-power klystrons are used as output tubes in UHF television transmitters, satellite communication, and radar transmitters, and to generate the drive power for modern particle accelerators.

2.1

How it works

• Klystrons amplify RF signals by converting the kinetic energy in a DC electron beam into radio frequency power. • A beam of electrons is produced by a thermionic cathode (a heated pellet of low work function material), and accelerated by high-voltage electrodes (typically in the tens of kilovolts). • This beam is then passed through an input cavity resonator. RF energy is fed into the input cavity at, or near, its resonant frequency, creating standing waves, which produce an oscillating voltage which acts on the electron beam. The electric field causes the electrons to ”bunch”: electrons that pass through when the electric field opposes their motion are slowed, while electrons which pass through when the electric field is in the same direction are accelerated, causing the previously continuous electron beam to form bunches at the input frequency. To reinforce the bunching, a klystron may contain additional ”buncher” cavities.

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• The beam then passes through a ”drift” tube in which the faster electrons catch up to the slower ones, creating the ”bunches”, then through a ”catcher” cavity. In the output ”catcher” cavity, each bunch enters the cavity at the time in the cycle when the electric field opposes the electrons’ motion, decelerating them. • Thus the kinetic energy of the electrons is converted to potential energy of the field, increasing the amplitude of the oscillations. The oscillations excited in the catcher cavity are coupled out through a coaxial cable or waveguide. The spent electron beam, with reduced energy, is captured by a collector electrode. • To make an oscillator, the output cavity can be coupled to the input cavity(s) with a coaxial cable or waveguide. Positive feedback excites spontaneous oscillations at the resonant frequency of the cavities.

Application • In modern systems, they are used from UHF (hundreds of MHz) up through hundreds of gigahertz (as in the Extended Interaction Klystrons in the CloudSat satellite). • Klystrons can be found at work in radar, satellite and wideband high-power communication (very common in television broadcasting and EHF satellite terminals), medicine (radiation oncology), and high-energy physics (particle accelerators and experimental reactors).



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shop.ssb cra ck.com Figure 2: A 325 Mhz klystron




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Microwave'Engineering'MCQs'

Microwave*Engineering*MCQs* ! 1.''Loss'angle'of'a'good'quality'cable'is'about' (a)' 1°' (b)' 30°' (c)' 70°' (d)' 90°' ' 2.''Which'of'the'following'lines'is'nonHradiating?' (a)' Open'two'wire' (b)' Coaxial' (c)' Both' (d)' None'of'the'above' ' 3.''Skin'effect'is'more'pronounced'at'high'frequencies.' (a)' True' (b)' False' (c)' Depends'on'the'voltage' (d)' Depends'on'the'current' ' 4.''A'10'km'long'line'has'a'characteristic'impedance'of'400'ohms.'If'line'length'is' 100'km,'the'characteristic'impedance'is' (a)' 4000'Ω' (b)' 400'Ω' (c)' 40'Ω' (d)' 4'Ω' ' 5.''The'correct'sequence'of'parts'in'klystron'amplifier'are' (a)' anode,'catcher'cavity,'cathode,' (b)' cathode,'buncher'cavity,'catcher' buncher'cavity' cavity,'cavity' (c)' anode,'buncher'cavity,'catcher' (d)' cathode,'catcher'cavity,'anode,' cavity,'cathode' buncher'cavity' ' 6.''A'cavity'resonator'is' (a)' a'hollow'metallic'enclosure' (b)' a'hollow'enclosure'having' magnetic'material'as'its'walls' (c)' a'hollow'enclosure'having' (d)' either'(b)'or'(c)' dielectric'material'as'its'walls' ' ' 7.''If'antenna'diameter'is'increased'four'times,'the'maximum'range'is'increased' by'a'factor'of' (a)' 2' (b)' 2' (c)' 4' (d)' 0.2' '

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8.''If'the'minimum'range'of'a'radar'is'to'be'doubled,'the'peak'power'has'to'be' increased'by'a'factor'of' (a)' 2' (b)' 4' (c)' 8' (d)' 16' ' 9.''The'Wavelength'correspond'to'Microwave'frequency'range'is' (a)' 30'to'300GHz' (b)' 3'''to'30'GHz' (c)' 0.3'to'3'Ghz' (d)' 300'to'3oooGHz' ' 10.'The'main'advantage'of'microwave'is'thatH' (a)' Highly'Directive' (b)' Moves'at'the'speed'of'light' (c)' S/N'ratio'greater' (d)' High'penetration'power' ' ' 11.''Reflex'Klystron'is'a'–' (a)' Ampilfier' (b)' Oscillator' (c)' Attenuator' (d)' Filter' ' 12.'Klystron'operates'on'the'principle'ofH' (a)' Amplitude'Modulation' (b)' Frequency'Modulation' (c)' Pulse'Modulation' (d)' Velocity'modulation' ' 13.'In'multicavity'Klystron'additional'cavities'are'inserted'between'buncher'and' catcher'cavities'to'achieveH' (a)' Higher'Gain' (b)' Higher'Efficiency' (c)' Higher'Frequency' (d)' Higher'Bandwidth' ' 14.'The'modes'in'the'reflex'Klystron'–' (a)' give'same'frequency'but' (b)' are'caused'by'spurious'frequency' different'transit'time' modulation' (c)' are'just'for'theoretical' (d)' result'from'excessive''transit'time' consideration' across'resonator'gap' 15.''A'reflex'Klystron'function'as' (a)' Microwave'Oscillator' (b)' Amplifier' (c)' Phase'shifter' (d)' Both'amplifier'and'phase'shifter' ' 16.'A'space'between'two'cavities'in'two'cavity'klystron'is'

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(a)' Drift'space' (c)' Running'space'

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(b)' Free'space' (d)' Normal'space'

' 17.'Magnetron'is'an' (a)' Amplifier' (b)' Oscillator' (c)' 'Phase'shifter' (d)' Both'phase'shifter'and'amplifier' ' 18.'TWT'is' (a)' Oscillator' (b)' Tuned'Amplifier' (c)' Wide'band'Amplifier' (d)' Both'amplifier'and'Oscillator' ' 19.''In'a'communication'system'noise'is'most'likely'to'affect'the'signal' (a)' at'the'transmitter' (b)' in'the'channel' (c)' in'the'information'source' (d)' at'the'destination' ' 20.''Indicate'the'false'statement'.modulation'is'used'to' (a)' reduce'the'bw'used' (b)' separate'different'transmissions' (c)' ensure' that' intelligence' may' (d)' allow'the'use'of'practical'antenna' be' transmitted' over' long' ' distances' ' 21.''One'of'the'following'noise'become'of'great'importance'at'high'frequency.it'is' the' (a)' shot'noise' (b)' random'noise' (c)' impulse'noise' (d)' transit'time'noise' ' ' 22.''The'value'of'the'resistor'creating'thermal'noise'is'doubled'.the'noise'power'is' (a)' halved' (b)' quadrupled' (c)' doubled' (d)' unchanged' ' 23.''The'o/p'stage'of'a'television'transmitter'is'most'likely'to'be'a' (a)' plate'modulated'class'c' (b)' grid'modulated'class'c'amplifier' amplifier' (c)' screen'modulated'class'c' (d)' grid'modulated'class'a'amplifier' amplifier' '

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24.'The'modulation'index'of'an'am'is'changed'from'0'to'1'.the'transmitted'power' is' (a)' unchanged' (b)' halved' (c)' doubled' (d)' increased'by'50%' ' 25.'AM''is'used'for'broadcasting'because' (a)' it'is'more'noise'immune'than' (b)' compared'with'other'it'requires' other'information'system' less'transmitting'power' (c)' its'use'avoids'receiver' (d)' no'other'modulation'system'can' complexity' provide'the'necessary'bw'for'high' fidelity' 26.''In'the'spectrum'of'a'FM'wave' (a)' the'carrier'frequency' (b)' the'amplitude'of'any'side'band' disappears'when'the' depends'on'the'modulation'index' modulation'index'is'large' (c)' the'total'number'of'sidebands' (d)' the'carrier'frequency'cannot' depends'on'the'modulation' disappear' index' ' 27.''The'difference'b/w'phase'n'frequency'modulation' (a)' is'purely'theoretical'because' (b)' ia'too'great'to'make'the'two' they'are'same'in'practice' system'compatible' (c)' lies'in'the'poorer'audio' (d)' lies'in'different'definitions'of'the' response'of'phase'modulation' modulation'index' ' 28.''Indicate'which'of'the'following'is'not'a'advantage'of'FM'over'AM' (a)' better'noise'immunity'is' (b)' lower'bw'is'required' provided' (c)' the'transmitted'power'is'more' (d)' less'modulating'power'is'required' useful' ' 29.''indicate'which'of'the'following'statements'about'the'advantage'of'the'phase' discriminator'over'the'slope'detector'is'false' (a)' much'easier'alignment' (b)' better'linearity' (c)' greater'limiting' (d)' fewer'tuned'circuit' ' 30.''In'a'ratio'detector'

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(a)' the'linearity'is'worse'than'in'a' phase'discriminator' (c)' the'o/p'is'twice'obtainable' from'a'similar'phase' discriminator'

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(b)' stabilization'against'signal' strength'variation'is'provided' (d)' the'o/p'is'twice'obtainable'from'a' similar'phase'discriminator'

' '31.''If'an'amplifier'is'used'as'the'first'af'amplifier'in'a'transistor'receiver,'this'will' have'the'effect'of' (a)' improving'the'effectiveness'of' (b)' reducing'the'effect'of'Hve'peak' the'agc' clipping' (c)' reducing'the'effect'of'noise'at' (d)' improving'the'selectivity'of'the' low'modulation'depths' receiver' ' 32.''The'image'frequency'of'an'superhetrodyne'receiver'is' (a)' is'created'within'the'receiver'it' (b)' is'due'to'insufficient'adjacent' self' channel'rejection' (c)' is'not'rejected'by'if'tuned' (d)' is'independent'of'the'frequency'at' circuits' which'the'receiver'is'tuned' ' 33.''One'of'the'main'function'of'the'rf'amplifier'in'superhetrodyne'receiver'is'to' (a)' provide'improve'tracking' (b)' permit'better'adjacent'channel' rejection' (c)' increase'the'tuning'range'of' (d)' improve'the'rejection'of'the' the'receiver' image'frequency' ' 34.'Indicate'the'false'statement.thw'swr'on'a'transmission'line'is'infinity',the'line' is'terminated'in' (a)' a'short'circuit' (b)' a'complex'impedance' (c)' an'open'circuit' (d)' a'pure'reactance' ' 35.''The'velocity'factor'of'a'transmission'line' (a)' depends'on'the'dielectric' (b)' increases'the'velocity'along'the' constant'of'the'material'used' transmission'line' (c)' is'governed'by'skin'effect' (d)' is'higher'for'a'solid'dielectric'than' for'air' '

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36.''For'transmission'line'load'matching'over'a'range'of'frequencies,'it'is'best'to' use'a' (a)' balun' (b)' broadband'directional'coupler' (c)' double'stab' (d)' single'stub'of'adjustable'position' ' 37.''The'main'disadvantage'of'the'two'hole'directional'coupler'is' (a)' low'directional'coupling' (b)' poor'directivity' (c)' high'swr' (d)' narrow'bw' ' 38.''To'couple'a'coaxial'line'to'a'parallelHwire',it'is'best'to'use'a' (a)' slotted'line' (b)' balun' (c)' directional'coupler' (d)' quarter'wave'transformer' ' 39.'Indicate'which'of'the'following'term'applies'to'troposcatter'propagation' (a)' sids' (b)' fading' (c)' atmospheric'storm' (d)' Faraday'rotation' ' 40.''VLF'waves'are'used'for'some'types'of'services'because' (a)' of'the'low'power'required' (b)' the'transmitting'antennas'are'of' convenient'size' (c)' they'r'very'reliable' (d)' they'penetrate'the'ionosphere' easily' ' 41.'High'frequency'waves'are' (a)' absorbed'by'the'f2'layer' (b)' reflected'by'the'd'layer' (c)' capable'of'use'for'long'distance' (d)' are'affected'by'solar'cycle' communication'on'the'moon' ' ' '42.''A'ship'to'ship'communication'plagnued'by'fading'.the'best'solution'seems'to' be'the'use'of' (a)' a'more'directional'antenna' (b)' a'broad'band'antenna' (c)' frequency'diversity' (d)' space'diversity' ' '43.''A'range'of'microwave'frequency'more'easily'passed'by'the'atmosphere'than' the'others'is'called'a' (a)' window' (b)' critical'frequency'

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(c)' gyro'frequency'range'

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(d)' resonance'in'atmosphere'

' 44.''Frequency'in'uhf'range'normally'propagate'by'means'of' (a)' ground'wave' (b)' sky'wave' (c)' surface'wave' (d)' space'wave' ' 45.''Tropospheric'scatter'is'used'with'frequency'in'the'following'range' (a)' HF' (b)' VHF' (c)' UHF' (d)' VLF' ' 46.''The'ground'waves'eventually'disappears',as'one'moves'away'from'the' transmitter'because'of' (a)' interference'from'the'sky'wave' (b)' loss'of'los'condition' (c)' maximum'single'hop'distance' (d)' tilting' limitation' ' 47.''In'em'waves',polarization' (a)' is'caused'by'reflection' (b)' is'due'to'inverse'nature'of'the' waves' (c)' result'from'the'longitudinal' (d)' is'always'vertical'in'an'isotropic' nature'of'the'waves' medium' ' 48.''An'em'wave'travels'in'the'free'space'only'one'of'the'following'can'happen'to' them' (a)' absorption' (b)' attenuation' (c)' refraction' (d)' reflection' ' '49.''The'absorption'of'radio'waves'by'the'atmosphere'depends'on' (a)' their'frequency' (b)' their'distance'from'the' transmitter' (c)' the'polarisation'of'the'wave' (d)' the'polarisation'of'the' atmosphere' ' 50.'em'waves'are'refracted'when'they' (a)' pass'in'to'medium'of'different' (b)' r'polarised'at'right'angles'to'the' dielectric'constants' direction'of'propagation' (c)' encounter'a'perfectly' (d)' pass'through'a'small'slot'in'a'

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conducting'surface'

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conducting'plane'

' '51.''Diffraction'of'em'waves' (a)' is'caused'by'reflections'from' (b)' arises'only'with'spherical'wave' the'ground' fronts' (c)' will'occur'when'the'waves'pas' (d)' may'occur'around'the'edges'of'a' through'a'large'slot' sharp'obstacle' ' 52.''When'mw'signals'follow'the'curvature'of'the'earth',this'is'known'as' (a)' the'Faraday'effect' (b)' ducting' (c)' tropospheric'scatter' (d)' ionospheric'reflection' ' '53.''Helical'antenna'r'often'used'for'satellite'tracking'at'vhf'due'to' (a)' troposcatter' (b)' superrefraction' (c)' ionospheric'refraction' (d)' the'faraday'effect' ' 54.''An'ungrounded'antenna'near'the'ground'' (a)' acts'as'a'single'antenna'of' (b)' is'unlikely'to'need'an'earth'mat' twice'the'height' (c)' acts'as'an'antenna'array' (d)' must'be'horizontally'polarised' ' 55.''Which'of'the'following'antenna'is'best'excited'from'a'wave'guide?' (a)' biconical' (b)' horn' (c)' helical' (d)' discone' ' '56.''Indicate'the'antenna'that'is'not'wideband' (a)' dicone' (b)' folded'dipole' (c)' helical' (d)' marconi' ' 57.''Which'one'of'the'following'is'not'apply'to'the'yagi'uda'antenna' (a)' good'bw' (b)' parasitic'elements' (c)' folded'dipole' (d)' high'gain' ' 58.''An'antenna'that'is'circularly'polarised'is'the' (a)' helical' (b)' small'circular'loop' (c)' parabolic'reflector' (d)' yagi'uda' '

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'59.''The'standard'reference'antenna'for'the'directive'gain'is'the' (a)' infinitesimal'dipole' (b)' isotropic'antenna' (c)' elementary'doublet' (d)' half'wave'dipole' ' 60.''Top'loading'is'done'with'an'antenna'in'order'to'increase'its' (a)' effective'height' (b)' bw' (c)' beam'width' (d)' i/p'capacitance' ' 61.''cassegrain'feed'is'used'with'a'parabolic'reflector'to' (a)' increase'the'gain'of'the'system' (b)' increase'the'beamwith'of'the' system' (c)' reduce'the'size'of'the'main' (d)' allow'the'feed'to'be'placed'at'a' reflector' convenient'point' ' 62.''Zoning'is'used'with'a'dielectric'antenna'in'order'to' (a)' reduce'the'bulk'of'the'lens' (b)' increase'the'bw'of'the'lens' (c)' permit'point'to'point'focusing' (d)' correct'the'curvature'of'the' wavefront'from'a'horn'that'is'too' short' ' 63.''A'helical'antenna'is'used'in'satellite'tracking'because'of'its' (a)' circular'polarisation' (b)' maneuverability' (c)' broad'bw' (d)' good'front'to'back'ratio' ' ' '64.''The'discone'antenna'is' (a)' a'useful'direction'finding' (b)' used'as'a'radar'receiving'antenna' antenna' (c)' circularly'polarised'like'other' (d)' useful'as'a'uhf'receiving'antenna' circular'antennas' ' '65.'One'of'the'following'is'not'a'omnidirectional'antenna' (a)' half'wave'dipole' (b)' logHpereodic' (c)' discone' (d)' marconi' ' '66.''When'em'wave'are'propagated'in'a'waveguide' (a)' they'travel'along'the'broader' (b)' the'reflected'from'the'wall'but'do'

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walls'of'the'guide' not'travel'along'them' (c)' they'travel'through'the' (d)' they'travel'along'all'4'walls'of'the' dielectric'without'touching'the' waveguide' wall' ' 67.''Waveguides'r'used'mainly'for'microwave'signals'because' (a)' they' depend' on' straight' line' (b)' losses'would'be'too'heavy'at' propagation' which' applies' to' lower'frequencies' microwaves'only' ' (c)' there' are' no' generators' (d)' they'would'be'too'bulky'at'lower' powerful' enough' to' excite' frequency' them'at'lower'frequency' ' '68.''The'wavelength'of'a'wave'in'a'waveguide' (a)' is'greater'than'in'free'space' (b)' depends'only'on'the'waveguide' dimensions'and'the'free'space' wavelength' (c)' is'inversely'proportional'to'the' (d)' is'directly'proportional'to'the' phase'velocity' group'velocity' ' 69.''Compared'with'the'equivalent'transmission'lines',3ghz'waveguides(indicate' false'statement)' (a)' r'less'lossy' (b)' can'carry'high'powers' (c)' r'less'bulky' (d)' have'lower'attenuation' ' '70.''When'a'particular'mode'is'excited'in'a'waveguide',there'appears'an'extra' electric'component'in'the'direction'of'propagation.'The'resulting'mode'is' (a)' transverse'electric' (b)' transverse'magnetic' (c)' longitudinal' (d)' transverse'electromagnetic' ' '71.''When'em'waves'are'reflected'at'an'angle'from'a'wall,their'wavelength'along' the'wall'is' (a)' same'as'in'free'space' (b)' the'same'as'the'wavelength' perpendicular'to'the'wall' (c)' shorter'because'of'the'doppler' (d)' greater'in'the'actual'direction'of' effect' propagation' '

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72.''As'a'result'of'reflections'from'a'plane'conducting'wall',em'waves'acquire'an' apparent'velocity'greater'than'the'velocity'of'light'in'space.'This'is'called'the' (a)' velocity'of'propagation' (b)' normal'velocity' (c)' group'velocity' (d)' phase'velocity' ' '73.'Indicate'the'false'statement'.when'the'free'space'wavelength'of'a'signal' equals'the'cutoff'wavelength'of'the'guide' (a)' the'group'velocity'becomes' (b)' phase'velocity'becomes'infinite' zero' (c)' the'characteristic'impedence'of' (d)' the'wavelength'within'the' the'guide'becomes'infinite' waveguide'becomes'infinite' ' '74.''The'dominant'mode'of'propagation'is'preferred'with'rectangular'wave' guides'because(indicate'the'false'statement)' (a)' it'leads'to'the'smallest' (b)' it'resulting'impedance'can'be' waveguide'dimensions' matched'directly'to'coaxial'lines' (c)' it'is'easier'ti'exite'than'the' (d)' propagation'of'it'without'any' other'modes' spurious'generation'can'be' ensured' ' 75.'A'choke''flange'may'be'used'to'couple'two'waveguides' (a)' to'help'in'alignment'of'the' (b)' because'it'is'simpler'than'any' waveguides' other'join' (c)' to'compensate'for' (d)' to'increase'the'bw'of'the'system' discontinuity'at'the'join' ' '76.''In'order'to''couple'two'generators'to'a'waveguide'system'without'coupling' them'to'each'other',one'could'not'use'a' (a)' rat'race' (b)' e'plane't' (c)' hybrid'ring' (d)' magic't' ' 77.''Which'of'the'following'waveguide'tuning'is'not'easily'adjustable' (a)' screw' (b)' stub' (c)' iris' (d)' plunger' ' 78.''A'piston'attenuator'is'a' (a)' vane'attenuator' (b)' waveguide'below'cutoff'

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(c)' mode'filter'

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(d)' flap'attenuator'

' 79.''Cylindrical'cavity'resonator'r'not'used'with'klystron'because'they'have' (a)' a'q'taht'is'too'low' (b)' a'shape'whose'resonant' frequency'is'too'difficult'to' calculate' (c)' harmonically'related'resonant' (d)' too'heavy'looses' frequency' ' 80.''A'directional'coupler'with'three'or'more'holes'is'sometimes'preferred'to'two' hole'coupler' (a)' because'it'is'more'efficient' (b)' to'increase'coupling'of'the'signal' (c)' to'reduce'spurious'mode' (d)' to'increase'the'bw'of'the'system' generation' ' 81.''A'ferrite'is' (a)' a' nonconductor' with' magnetic' (b)' an' inter' metallic' compound' with' properties' particularly'good'conductivity' (c)' an' insulator' with' heavily' (d)' a'microwave'semiconductor' attenuates'magnetic'fields' invented'by'faraday' ' 82.''A'manganese'ferrite'may'be'used'as'a'(indicate'false'statement)' (a)' circulator' (b)' isolator' (c)' garnet' (d)' phase'shifter' ' 83.''A'pin'diode'is' (a)' a'metal'semiconductor'point' (b)' a'microwave'mixer'diode' contact'diode' (c)' often'used'as'a'microwave' (d)' suitable'for'use'as'a'microwave' detector' switch' ' 84.''A'duplexer'is'used' (a)' to'couple'two'different' (b)' to'allow'the'one'antenna'to'be' antennas'to'a'transmitter' used'for'reception'or'transmission' without'mutual'interference' without'mutual'interference' (c)' to'prevent'interference'b/w' (d)' to'increases'the'speed'of'the' two'antennas'when'they'are' pulses'in'a'pulsed'radar'

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connected'to'a'receiver' ' 85.''For'some'application'circular'waveguide'may'be'preferred'over'rectangular' one'because'of' (a)' the'smaller'cross'section' (b)' lower'attenuation' needed'at'any'frequency' (c)' freedom'from'spurious'modes' (d)' rotation'of'polarisation' ' 86.''Indicate'which'of'the'following'cannot'be'followed'by'the'word'waveguide' (a)' elliptical' (b)' flexible' (c)' coaxial' (d)' ridged' ' 87.''In'order'to'reduce'cross'sectional'dimensions,the'waveguide'to'use'is' (a)' circular' (b)' ridged' (c)' rectangular' (d)' flexible' ' 88.''For'low'attenuation'best'transmission'medium'is' (a)' flexible'waveguide' (b)' ridged'waveguide' (c)' rectangular'waveguide' (d)' coaxial'line' ' '89.''A'microwave'tube'amplifier'uses'an'axial'magnetic'field'and'a'radial'electric' field'.'This'is'a' (a)' reflex'klystron' (b)' coaxial'magnetron' (c)' travelling'wave'magnetron' (d)' cfa' ' ' 90.''One'of'the'reason'why'vaccum'tubes'eventually'fail'at'''microwave' frequencies'is'that'their' (a)' nf'increase' (b)' transit'time'become'too'short' (c)' shunt'capacitive'reactances' (d)' series'inductive'reactances' become'too'large' become'too'small' ' 91.'Indicate'the'false'statement'.transit'time'in'microwave'tube'will'be'reduced'if' (a)' the'electrodes'are'brought' (b)' a'higher'anode'current'is'used' together' (c)' multiple'or'coaxial'leads'r'used' (d)' the'anode'voltage'is'made'large' '

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92.''The'multicavity'klystron' (a)' is'not'a'good'low'level' amplifier'because'of'noise' (c)' is'not'suitable'for'pulsed' operation'

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(b)' has'a'high'repeller'voltage'to' ensure'a'rapid'transit'time' (d)' needs' a' long' transit' time' through' the' buncher' cavity' to' ensure' current'modulation'

' 93.''Indicate'the'false'statement.'Klystron'amplifiers'may'use'intermediate' cavities'to' (a)' prevent' the' oscillations' that' (b)' increase'the'bw' occurs'in'two'cavity'klystron' (c)' improve'the'power'gain' (d)' increase'the'efficiency'of'the' klystron' ' 94.'The'cavity'magnetron'use'strapping'to' (a)' prevent'mode'jumping' (b)' prevent'cathod'back'heating' (c)' ensure'bunching' (d)' improve'the'phase'focusing' ' 95.''A'magnetic'field'is'used'in'the'cavity'magnetron'to' (a)' prevent'anode'current'in'the' (b)' ensure'that'the'oscillations'r' absence'of'oscillations' pulsed' (c)' help'in'focusing'the'electron' (d)' ensure'that'the'electrones'will' beam,'thus'preventing' orbit'around'the'cathod' spreading' ' '96.'The'primary'purpose'PF'the'helix'in'the'TWT'is' (a)' prevent'the'electron'beam' (b)' reduce'axial'velocity'of'the'rf'field' spreading'in'the'long'tube' (c)' ensure'broadband'operation' (d)' reduce'the'noise'figure' ' 97.'The'attenuator'in'the'TWT'is'used'for' (a)' help'focusing' (b)' prevent'oscillations' (c)' prevent'saturatuion' (d)' increase'gain' ' 98.'Periodic'permanent'magnet'focusing'is'used'with'TWT'to' (a)' allow'pulsed'operation' (b)' improve'electron'bunching' (c)' avoid'the'bulk'of'an' (d)' allow'coupled'cavity'operation'at'

'


electromagnet'

'


the'high'frequency'

' 99.''A'magnetron'whose'oscillating'frequency'is'electronically'adjustable'over'a' wide'range'is'called' (a)' coaxial'magnetron' (b)' ditcher'tuned'magnetron' (c)' frequency'agile'magnetron' (d)' vtm' ' 100.'A'ruby'maser'amplifier'must'be'cooled' (a)' because'maser'amplifiers' (b)' to'increase'bw' generats'a'lot'of'heat' (c)' because'it'can'not'operate'at' (d)' to'improve'the'noise'performance' room'temp' ' ' ' 101.'The'transmission'system'using'two'ground'planes'is' (a)' microstrip' (b)' elliptical'waveguide' (c)' parallel'wire'line' (d)' stripline' ' 102.'Surface'acoustic'wave'propagate'in' (a)' gallium'arsenide' (b)' indium'phosphste' (c)' stripline' (d)' quartz'crystal' ' 103.'Saw'devices'may'be'used'as' (a)' transmission'media'like' (b)' filters' stripline' (c)' UHF'amplifiers' (d)' oscillator'at'milimiter'frequency' ' 104.'Indicate'the'false'statement.'Fet's'r'preferred'to'bipolar'transistor'at'the' highest'frequencies'because'they'are' (a)' less'noisy' (b)' lend'themselves'more'readily'to' integration' (c)' are'capable'of'higher' (d)' can'provide'higher'gain' efficiencies' ' 105.'The'biggest'advantage'of'the'trapatt'diode'over'the'impatt'diode'is'it's' (a)' lower'noise' (b)' higher'efficiency'

'


(c)' ability'to'operate'at'higher' frequency'

'


(d)' lesser'sensitivity'to'harmonics'

' '106.'Indicate'which'of'the'following'diode'will'produce'the'highest'pulsed'power' o/p' '' (a)' varactor' (b)' gunn' (c)' schottky'diode' (d)' rimpatt'diode' ' 107.'Indicate'which'of'the'following'diode'does'not'uses'Hve'resistance'in'it's' operation' (a)' backward' (b)' gunn' (c)' impatt' (d)' tunnel' ' 108.''One'of'the'following'is'not'used'as'a'microwave'mixer'or'detector' (a)' crystal'diode' (b)' schottky'barrier'diode' (c)' backward'diode' (d)' pin'diode' ' 109.'One'of'the'following'microwave'diode'is'suitable'for'very'low'power' oscillator'only' (a)' tunnel' (b)' avalanche' (c)' gunn' (d)' impatt' ' 110.'The'gain'bw'frequency'of'a'microwave'transistor,'is'the'frequency'at'which' (a)' alpha'of'the'transistor'falls'by' (b)' beta'of'the'transistor'falls'by'3'db' 3db' (c)' power'gain'of'the'transistor' (d)' beta'of'the'transistor'falls'to'unity' falls'to'unity' ' 111.''A'varactor'diode'may'be'useful'at'microwave'frequency(indicate'the'false' statement)' (a)' for'electronic'tunning' (b)' for'frequency'multiplication' (c)' as'an'oscillator' (d)' as'a'paramatric'amplifier' ' '' 112.'For'a'microwave'transistor'to'operate'at'the'highest'frequency(indicate'the' false'statement)'

'


'


(a)' collector'voltage'must'be'large' (b)' collector'current'must'be'large' (c)' base'should'be'thin' (d)' emitter'area'must'be'large' ' '113.'If'high'order'frequency'multiplication'is'required'from'a'diode'multiplier' (a)' the'resistive'cutoff'frequency' (b)' a'small'value'of'base'resistance'is' must'be'high' required' (c)' a'step'recovery'diode'must'be' (d)' a'large'range'of'capacitance' used' variation'is'needed' 114.'The'tunnel'diode' (a)' has' a' tiny' hole' through' it's' (b)' is'a'point'contact'diode'with'a' center'to'facilitate'tunneling' very'high'reverse'resistance' (c)' uses'a'high'doping'level'to' (d)' works'by'quantam'tunneling' provide'a'narrow'junction' exhibited'by'gallium'arsenide'only' ' 115.'A'tunnel'diode'is'losely''coupled'to'it's'cavity'in'order'to' (a)' increase'the'frequency'stability' (b)' increase'the'available'Hve' resistance' (c)' faciliting'tunning' (d)' allow'operation'at'the'high' frequency' ' '116.'The'Hve'resistance'in'a'tunnel'diode' (a)' is'a'maximum'at'the'peak'point' (b)' is'available'b/w'peak'n'vally'point' of'the'characteristics' (c)' is'maximum'at'valley'point' (d)' may'be'improved'by'use'of' reverse'bias' ! ! !

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Answers:*Microwave*Engineering*MCQs*

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Antenna and Wave Propagation

Contents 1 Antenna parameters 1.1 Self impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Mutual impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 5 6

2 Wave propagation

7

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1

Page: 2

1

Antenna parameters

Antennas are metallic structures designed for radiating and receiving electromagnetic energy. An antenna acts as a transitional structure between the guiding device. Antenna: That part of a transmitting or receiving system that is designed to radiate or receive electromagnetic waves The radiation from an antenna can be explained with the help of Figure shown below a voltage source connected to a two conductor transmission line. When a sinusoidal voltage is applied across the transmission line, an electric field is created which is sinusoidal in nature and these results in the creation of electric lines of force which are tangential to the electric field. The magnitude of the electric field is indicated by the bunching of the electric lines of force. The free electrons on the conductors are forcibly displaced by the electric lines of force and the movement of these charges causes the flow of current which in turn leads to the creation of a magnetic field.

shop.ssb cra ck.com Due to the time varying electric and magnetic fields, electromagnetic waves are created and these travel between the conductors. As these waves approach open space, free space waves are formed by connecting the open ends of the electric lines. Since the sinusoidal source continuously creates the electric disturbance, electromagnetic waves are created continuously and these travel through the transmission line, through the antenna and are radiated into the free space. Inside the transmission line and the antenna, the electromagnetic waves are sustained due to the charges, but as soon as they enter the free space, they form closed loops and are radiated.

Effective length For antennas which are not defined by a physical area, such as monopoles and dipoles consisting of thin rod conductors, the aperture bears no obvious relation to the size or area of the antenna. An alternate measure of antenna gain that has a greater relationship to the physical structure of such antennas is effective length Ief f measured in meters, which is defined for a receiving antenna as: Ief f = V0 /Es where, V0 is the open circuit voltage appearing across the antenna’s terminals. Es is the electric field strength of the radio signal, in volts per meter, at the antenna. The longer the effective length the more voltage and therefore the more power the antenna will receive. Note, however, that an antenna’s gain or Aef f increases according to the square of lef f , and that this proportionality also involves the antenna’s radiation resistance.



Page: 3

Effective Aperture Antenna aperture or effective area is a measure of how effective an antenna is at receiving the power of radio waves. The aperture is defined as the area, oriented perpendicular to the direction of an incoming radio wave, which would intercept the same amount of power from that wave as is produced by the antenna receiving it. At any point, a beam of radio waves has an irradiance or power flux density (PFD) which is the amount of radio power passing through a unit area. If an antenna delivers an output power of Po watts to the load connected to its output terminals when irradiated by a uniform field of power density PFD watts per square meter, the antenna’s aperture Aef f in square meters is given by Po PFD So the power output of an antenna in watts is equal to the power density of the radio waves in watts per square meter, multiplied by its aperture in square meters. The larger an antenna’s aperture is, the more power it can collect from a given field of radio waves. To actually obtain the predicted power available Po , the polarization of the incoming waves must match the polarization of the antenna, and the load (receiver) must be impedance matched to the antenna’s feed point impedance. Aef f =

Aperture and Gain The directivity of an antenna, its ability to direct radio waves in one direction or receive from a single direction, is measured by a parameter called its gain, which is the ratio of the power received by the antenna to the power that would be received by a hypothetical isotropic antenna, which receives power equally well from all directions. It can be shown that the aperture of a lossless isotropic antenna, which by definition has unity gain, is: ⁄2 4fi where, ⁄ is the wavelength of the radio waves. So the gain of any antenna is proportional to its aperture: Aef f =

shop.ssb cra ck.com G=

4fiAef f ⁄2

Beamwidth Half Power Beam Width (HPBW) of an antenna The main beam is the angular region where primarily the radiation goes. The effective width of the antenna mainÔ beam called the HPBW is defined as the angular separation between directions where the field reduces to 1/ 2 of its maximum value. Since the power density of a wave is proportional to the square of the electric Ô field, when the electric field reduces to 1/ 2 of its maximum value, the power density reduces to 1/2 of its maximum value. That is, the power density reduces by 3-dB. The HPBW therefore is also referred to as the 3-dB Beam width. There two HPBWs, one for the E-plane pattern and other for the H-plane pattern. For the Hertz dipole, the E-plane HPBW is 900 and the H-plane HPBW is not defined since the radiation pattern is constant in the H-plane. The HPBW is a better measure of the effective width of the main beam of the antenna compared to BWFN because there are situations when the effective width of the antenna beam changes but the BWFN remains same.

Polarization The polarization of the EM field describes the orientation of its vectors at a given point and how it varies with time. In other words, it describes the way the direction and magnitude of the field vectors (usually E) change in time. Polarization is associated with TEM time-harmonic waves where the H vector relates to the E vector simply by H = r¯ ◊


E ÷


Page: 4 In antenna theory, we are concerned with the polarization of the field in the plane orthogonal to the direction of propagation-this is the plane defined by the vectors of the far field. The polarization is the locus traced by the extremity of the time-varying field vector at a fixed observation point. According to the shape of the trace, three types of polarization exist for harmonic fields: linear, circular and elliptical. Any polarization can be represented by two orthogonal linear polarizations, (Ex , Ey ) or (EH , EV ), whose fields are out of phase by an angle of ”L .

Directivity The directivity of an antenna is the maximum value of its directive gain. Directive gain is represented as D(◊„) and compares the radiation intensity (power per unit solid angle) that an antenna creates in a particular direction against the average value over all directions: D(◊, „) =

U T otal radiated power/(4fi)

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where, ◊ and „ are the standard spherical coordinates angles U is the radiation intensity The beam solid angle, represented as A , is defined as the solid angle which all power would flow through if the antenna radiation intensity were constant and maximum value. If the beam solid angle is known, then directivity can be calculated as: D=

4fi A

which simply calculates the ratio of the beam solid angle to the total surface area of the sphere it intersects.

Gain Analogously to the directivity factor, the gain G is the ratio of the radiation intensity Fmax obtained in the main direction of radiation to the radiation intensity Fi0 that would be generated by a loss-free isotropic radiator with the same input power Pt0 G = Fmax /Fi0 Where, G = Fmax /Fi0 In contrast to the directivity factor, the antenna efficiency ÷ is taken into account in the above equation since the following applies: G = ÷D Gain and directivity factor are often expressed in a logarithmic form: g = 10logG[dB]


and

d = 10logD[dB]


Page: 5

Radiation Resistance In general, an antenna radiates power into free space in the form of electromagnetic waves. So the power dissipated is given by, W Õ = I 2 .R Assuming all the power dissipated in the form of electromagnetic waves, then we can write, WÕ R2 The resistance which relates power radiated by radiating antenna and the current flowing through the antenna is a fictitious resistance. Such resistance is called radiation resistance of antenna and it is denoted by Rrad or Rr or Ro . The radiation resistance is a fictitious resistance such that when it is connected in series with antenna dissipates same power as the antenna actually radiates. But practically the energy supplied to the antenna is not completely radiated in the form of electromagnetic waves, but there are certain radiation losses due to the loss resistance denoted by Rloss . Thus the total power is given by, R=

W = I 2 (Rrad + Rloss ) Note: The radiation resistance of antenna depends on antenna configuration, ratio of length and diameter of conductor used, location of the antenna with respect to ground and other objects.

Antenna efficiency In antenna theory, radiation efficiency, which is often abbreviated to just efficiency is a figure of merit for an antenna. It is a measure of the electrical losses that occur in the antenna. Radiation efficiency is defined as ”The ratio of the total power radiated by an antenna to the net power accepted by the antenna from the connected transmitter.” It is sometimes expressed as a percentage. It will be frequency dependent. The gain of an antenna is the directivity multiplied by the radiation efficiency. Antenna efficiency is the ratio between its radiation resistance and its total resistance:

shop.ssb cra ck.com Eradiation ≠

P P Rradiation ≠ ≠ Po P +P Rtotal

Where, Po = active power P = radiation power P = power of losses Efficiency of a transmitting antenna is the ratio of power actually radiated (in all directions) to the power absorbed by the antenna terminals. The power supplied to the antenna terminals which is not radiated is converted into heat. This is usually through loss resistance in the antenna’s conductors. The efficiency of an antenna is equal to Rradiation Rradiation + Rtotal

Impedance and Directional characteristics 1.1

Self impedance

The impedance of antenna measured at the terminals where transmission line carrying R.F. power connected is called antenna input impedance. These terminals are nothing but feed points of the antenna, the impedance is also called feed point impedance or terminal impedance. As the R.F. power carried by the transmission line from the transmitter, excites or drives the antenna, the antenna input impedance can be alternatively called driving point impedance of antenna.



Page: 6

When the antenna is lossless and isolated from ground and other objects, the impedance offered by antenna to the transmission line is represented by two terminal networks with impedance ZL as shown in the figure above. ZL represents that the antenna impedance acts as load to the transmission line driving antenna. With a lossless and isolated antenna, the antenna terminal impedance is same as the self impedance of the antenna, which is represented by Z11 . The self impedance of the antenna is a complex quantity given by, Z11 = R11 + jX11 The real part of Z11 i.e. R11 is called self resistance or radiation resistance of antenna, while the imaginary part of Z11 i.e. X11 is called self reactance of antenna.

1.2

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Mutual impedance

While considering the self impedance of antenna, we assumed that the antenna is lossless and isolated from the other objects and ground. But many times in the large antenna systems, any antenna may be placed in the close vicinity of other active antennas. In such cases, the antenna terminal impedance is not simply equal to the self impedance of the antenna but another impedance gets introduced due to the currents flowing in other active antennas placed close to the antenna considered. Such impedance is called mutual impedance of antenna. Before discussing mutual impedance of antenna, let us consider the coupled circuits with two circuits kept very closed to each other. When current flows in circuit-1, the voltage is induced at the open terminals of circuit-2. Similarly the current flowing in circuit-2 induces voltage at the open terminals of circuit-1

Thus the mutual impedance of the coupled circuit is defined as negative ratio of the voltage induced at the open terminals of once circuit to the current in other circuit. Mathematically we can write, Z21 = ≠

V2 1 I1

Z12 = ≠

V1 2 I2

Let us consider two antennas kept very closed to each other (such antennas may be called coupled antennas) as shown in below



Page: 7

Exactly on the similar lines to the coupled circuits, the mutual impedance of the antenna is given by Z21 = ≠

V2 1 I1

Z12 = ≠

V1 2 I2

But according to reciprocity theorem, we can write mutual impedance of antenna as, Zm =

V21 V12 = I1 I2

Mutual impedance depends on: • Magnitude of induced voltage

• Phase difference between induced voltage and input current, • Tuning conditions of coupled antennas.

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Charecteristics

A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources. Directional antennas likeYagi-Uda antennas provide increased performance over dipole antennas when a greater concentration of radiation in a certain direction is desired. All practical antennas are at least somewhat directional, although usually only the direction in the plane parallel to the earth is considered, and practical antennas can easily be omnidirectional in one plane. The main characteristics of antenna are the radiation pattern. The antenna pattern is a graphical representation in three dimensions of the radiation of the antenna as a function of angular direction. Antenna radiation performance is usually measured and recorded in two orthogonal principal planes (E-Plane and Hplane or vertical and horizontal planes). The pattern of most base station antennas contains a main lobe and several minor lobes, termed side lobes.

2

Wave propagation

Reflection Reflection of light is an everyday occurrence. Mirrors are commonplace and can be seen in houses and many other places. Shop windows also provide another illustration for this phenomenon, as do many other areas. Radio waves are similarly reflected by many surfaces. When reflection occurs, it can be seen that the angle of incidence is equal to the angle of reflection for a conducting surface as would be expected for light. When a signal is reflected there is normally some loss of the signal, either through absorption, or as a result of some of the signal passing into the medium. A variety of surfaces can reflect radio signals. For long distance communications, the sea provides one of the best reflecting surfaces. Other wet areas provide good reflection of radio signals. Desert areas are poor reflectors and other types of land fall in between these two extremes. In general, though, wet areas provide better reflectors.



Page: 8 For relatively short range communications, many buildings, especially those with metallic surfaces provide excellent reflectors of radio energy. There are also many other metallic structures such as warehouses that give excellent reflecting surfaces. As a result of this signals travelling to and from cellular phones often travel via a variety of paths. Similar effects are noticed for Wi-Fi and other short range wireless communications. An office environment contains many surfaces that reflect radio signals very effectively.

Refraction It is also possible for radio waves to be refracted. The concept of light waves being refracted is very familiar, especially as it can be easily demonstrated by placing a part of stick or pole in water and leaving the remaining section in air. It is possible to see the apparent change or bend as the stick enters the water. Mirages also demonstrate refraction and a very similar effect can be noticed on hot days when a shimmering effect can be seen when looking along a straight road. Radio waves are affected in the same way. It is found that the direction of an electromagnetic wave changes as it moves from an area of one refractive index to another. The angle of incidence and the angle of refraction are linked by Snell’s Law that states: n1 sin(◊1 ) = n2 sin(◊2 ) For radio signals there are comparatively few instances where the signals move abruptly from a region with one refractive index, to a region with another. It is far more common for there to be comparatively gradual change. This causes the direction of the signal to bend rather than undergo an immediate change in direction.

Diffraction Radio signals may also undergo diffraction. It is found that when signals encounter an obstacle they tend to travel around them. This can mean that a signal may be received from a transmitter even though it may be ”shaded” by a large object between them. This is particularly noticeable on some long wave broadcast transmissions. For example the BBC long wave transmitter on 198 kHz is audible in the Scottish glens where other transmissions could not be heard. As a result the long wave transmissions can be heard in many more places than transmissions on VHF FM. To understand how this happens it is necessary to look at Huygen’s Principle. This states that each point on a spherical wave front can be considered as a source of a secondary wave front. Even though there will be a shadow zone immediately behind the obstacle, the signal will diffract around the obstacle and start to fill the void. It is found that diffraction is more pronounced when the obstacle becomes sharper and more like a ”knife edge”. For a radio signal a mountain ridge may provide a sufficiently sharp edge. A more rounded hill will not produce such a marked effect. It is also found that low frequency signals diffract more markedly than higher frequency ones. It is for this reason that signals on the long wave band are able to provide coverage even in hilly or mountainous terrain where signals at VHF and higher would not.

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Ground wave propagation The ground wave is actually composed of two separate component waves. These are known as the SURFACE WAVE and the SPACE WAVE.



Page: 9 The determining factor in whether a ground wave component is classified as a space wave or a surface wave is simple. A surface wave travels along the surface of the Earth. A space wave travels over the surface. The surface wave reaches the receiving site by travelling along the surface of the ground as shown in figure below. A surface wave can follow the contours of the Earth because of the process of diffraction. When a surface wave meets an object and the dimensions of the object do not exceed its wavelength, the wave tends to curve or bend around the object. The smaller the object, the more pronounced the diffractive action will be.

As a surface wave passes over the ground, the wave induces a voltage in the Earth. The induced voltage takes energy away from the surface wave, thereby weakening, or attenuating, the wave as it moves away from the transmitting antenna. To reduce the attenuation, the amount of induced voltage must be reduced. This is done by using vertically polarized waves that minimize the extent to which the electric field of the wave is in contact with the Earth. When a surface wave is horizontally polarized, the electric field of the wave is parallel with the surface of the Earth and, therefore, is constantly in contact with it. The wave is then completely attenuated within a short distance from the transmitting site. On the other hand, when the surface wave is vertically polarized, the electric field is vertical to the Earth and merely dips into and out of the Earth’s surface. For this reason, vertical polarization is vastly superior to horizontal polarization for surface wave propagation. Space wave follows two distinct paths from the transmitting antenna to the receiving antennaâ one through the air directly to the receiving antenna, the other reflected from the ground to the receiving antenna.

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Sky wave Skywave refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the short-wave frequency bands. As a result of skywave propagation, a signal from a distant AM broadcasting station, a short-wave station, or during sporadic E propagation conditions (principally during the summer months in both hemispheres)-a low frequency television station can sometimes be received as clearly as local stations. Most long-distance short-wave (high frequency) radio communication between 3 and 30 MHz is a result of skywave propagation.

Troposcatter propagation Tropospheric scatter (also known as troposcatter) is a method of communicating with microwave radio signals over considerable distances - often up to 300 km, and further depending on terrain and climate factors. This method of propagation uses the tropospheric scatter phenomenon, where radio waves at particular frequencies are randomly scattered as they pass through the upper layers of the troposphere. Radio signals are transmitted in a tight beam aimed at the highest point on the horizon in the direction of the receiver station. As the signals pass through the troposphere, some of the energy is scattered back toward the Earth, allowing the receiver station to pick up the signal. Normally, signals in the microwave frequency range used, around 2 GHz, travel in straight lines, and so are limited to line of sight applications, in which the receiver can be ’seen’ by the transmitter. So commu-



Page: 10 nication distances are limited by the visual horizon to around 30-40 miles. Troposcatter allows microwave communication beyond the horizon. Because the troposphere is turbulent and has a high proportion of moisture the tropospheric scatter radio signals are refracted and consequently only a proportion of the radio energy is collected by the receiving antennas. Frequencies of transmission around 2 GHz are best suited for tropospheric scatter systems as at this frequency the wavelength of the signal interacts well with the moist, turbulent areas of the troposphere, improving signal to noise ratios.

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'

Antenna'and'Wave'Propagation'MCQs'

Antenna&and&Wave&Propagation&MCQs& Antenna&Propagation! 1.'If'an'antenna'is'too'short'for'the'wavelength'being'used,'the'effective'length'can'be' increased'by'adding:'

'

(a)' capacitance'in'series' (c)' resistance'in'parallel'

(b)' inductance'in'series' (d)' resistance'in'series'

2.''Which'of'the'following'antennas'is'used'for'testing'and'adjusting'a'transmitter'for' proper'modulation,'amplifier'operation'and'frequency'accuracy?' (a)' Elementary' (c)' Isotropic'

(b)' Real' (d)' Dummy'

' 3.''The'power'fed'to'a'twoNbay'turnstile'antenna'is'100'watts.'If'the'antenna'has'a'2'dB' power'gain,'what'is'the'effective'radiated'power?'

'

(a)' 317'watts' (c)' 200'watts'

(b)' 158'watts' (d)' 400'watts'

4.''Which'of'the'following'antennas'receive'signals'in'the'horizontal'plane'equality'well' from'all'directions?' (a)' Horizontal'Hertz'antenna' (c)' Vertical'Yagi'antenna' '

(b)' Vertical'loop'antenna' (d)' A'vertical'antenna'which'is'a'quarterN wavelength'long'

5.''The'parasitic'element'of'an'antenna'system'will' (a)' decrease'its'directivity' (c)' give'the'antenna'unidirectional' properties' ' '

'

'

(b)' increase'its'directivity' (d)' both'B'and'C'


'


6.''A'vertical'loop'antenna'has'a'

'

(a)' unidirectional'radiation'pattern'in' (b)' unidirectional'radiation'pattern'in' the'horizontal'plane' the'vertical'plane' (c)' omnidirectional'radiation'pattern' (d)' a'bidirectional'radiation'pattern'in' in'the'horizontal'plane' the'horizontal'plane'

7.''What'is'the'electrical'wavelength'of'a'500'MHz'signal?'

'

(a)' 60'centimeters' (c)' 0.06'meter'

(b)' 6'meters' (d)' 60'meters'

8.''If'the'antenna'current'is'doubled,'the'field'strength'at'a'particular'position'is'

'

(a)' doubled' (c)' multiplied'by'a'factor'of'four'

(b)' halved' (d)' divided'by'a'factor'of'four'

9.''Which'one'of'the'following'antennas'radiates'equally'in'all'directions?'

'

(a)' Vertical'antenna' (c)' Horizontal'antenna'

(b)' isotropic'antenna' (d)' Dipole'antenna'

10.''Actual'height'of'antenna'should'be'at'least'

'

(a)' one'wavelength' (c)' quarter'wavelength'

(b)' half'wavelength' (d)' threeNfourth'wavelength'

11.''Which'antenna'is'not'properly'terminated?'

'

(a)' Resonant' (c)' Isotropic'

(b)' NonNresonant' (d)' Whip'

12.''______'is'an'antenna'array'which'is'highly'directional'at'right'angles'to'the'plane'of' the'array?'

' '

(a)' Broadside'array' (c)' Turnstile'array'

(b)' EndNfire'array' (d)' LogNperiodic'array'


'


13.''The'purpose'of'stacking'elements'on'an'antenna.'

'

(a)' Sharper'directional'pattern' (c)' Improved'bandpass'

(b)' Increased'gain' (d)' All'of'the'above'

14.''A'theoretical'reference'antenna'that'provides'a'comparison'for'antenna' measurements.'

'

(a)' Marconi'antenna' (c)' YagiNUda'array'

(b)' Isotropic'radiator' (d)' Whip'antenna'

15.''A'Hertz'antenna'is'operating'on'a'frequency'of'2182'kHz'and'consists'of'a'horizontal' wire'that'is'hanged'between'two'towers.'What'is'the'frequency'of'its'third'harmonic?'

'

(a)' 727'kHz' (c)' 436'kHz'

(b)' 6546'kHz' (d)' 6.546'kHz'

16.'Increasing'the'electrical'length'of'an'antenna'means'

'

(a)' add'an'inductor'in'parallel' (c)' add'an'inductor'series'

(b)' add'a'capacitor'in'series' (d)' add'a'resistor'is'series'

17.''What'is'antenna'bandwidth?' (a)' Antenna'length'divided'by'the' number'of'elements' (c)' The'angle'formed'between'two' imaginary'lines'drawn'through' '

(b)' The'angle'between'the'halfNpower' radiation'points' (d)' The'frequency'range'over'which'an' antenna'can'be'expected'to'operate' satisfactorily'

18.''To'lengthen'an'antenna'electrically,'add'a'

' '

'

(a)' resistor' (c)' condult'

(b)' battery' (d)' coil' '


'


19.''What'is'the'usual'electrical'length'of'a'driven'element'in'an'HF'beam'antenna?'

'

(a)' 1/4''wavelength' (c)' 1/2'wavelength'

(b)' 3/4'wavelength' (d)' 1'wavelength'

20.''What'happens'to'the'bandwidth'of'an'antenna'as'it'is'shortened'through'the'use'of' loading'coils?'

'

(a)' It'is'increased' (c)' No'change'occurs'

(b)' It'is'decreased' (d)' It'becomes'flat'

21.'It'is'useful'to'refer'to'an'isotropic'radiator.' (a)' when'comparing'the'gains'of' directional'antennas' (c)' when'(in'the'northern' hemisphere)'directing'the' transmission'

(b)' when'testing'a'transmission'line'for' standing'wave'ratio' (d)' when'using'a'dummy'load'to'tune'a' transmitter'

' 22.''A'disadvantage'of'using'a'trap'antenna.' (a)' It'will'radiate'harmonics'

'

(c)' It'is'too'sharply'directional'at' lower'frequencies'

(b)' It'can'only'be'used'for'singleNbad' operation' (d)' It'must'be'neutralized'

23.''The'input'terminal'impedance'at'the'center'of'a'folded'dipole'antenna'is'

'

(a)' 72'Ω' (c)' 50'Ω'

(b)' 300'Ω' (d)' 73'Ω'

24.'For'a'shortened'vertical'antenna,'where'should'a'loading'coil'be'placed'to'minimize' losses'and'produce'the'most'effective'performance?' (a)' As'low'as'possible'on'the'vertical' radiator' (c)' As'close'to'the'transmitter'as' possible' '

(b)' Near'the'center'of'the'vertical' radiator' (d)' At'a'voltage'node'


'


' 25.'The'effect'of'adding'parasitic'elements'of'a'Hertz'dipole'is'to'

'

(a)' make'the'antenna'more' (b)' reduce'its'resonant'frequency' omnidirectional' (c)' increase'the'antenna’s'power'gain' (d)' All'of'these'

26.''The'antenna'efficiency'of'an'HF'grounded'vertical'antenna'can'be'made' comparable'to'that'of'a'halfNwave'antenna'

'

(a)' By'installing'a'good'ground'radial' system' (c)' By'shortening'the'vertical'

(b)' By'isolating'the'coax'shield'from' ground' (d)' By'lengthening'the'vertical'

27.''An'antenna'“efficiency”'is'computed'by'using'one'of'the'following'equations.' (a)' Efficiency'='(radiation'resistance'/' (b)' Efficiency'='(total'resistance'/' transmission'resistance)' radiation'resistance)'x'100%' (c)' Efficiency'='(effective'radiated' (d)' Efficiency'='(radiation'resistance'/' power'/'transmitter'output)'x' total'resistance)'x'100%' 100%' ' 28.''Factors'that'determine'the'radiation'resistance'of'an'antenna'

'

(a)' Transmission'line'length'and' height'of'antenna' (c)' It'is'a'constant'for'all'antennas' since'it'is'physical'

(b)' The'location'of'the'antenna'with' respect'to'nearby'objects' (d)' Sunspot'activity'and'the'time'of'day'

29.'''_____'is'the'angle'between'the'halfNpower'radiation'points'

' '

'

(a)' Critical'angle' (c)' Angle'of'elevation' '

(b)' Beamwidth' (d)' Azimuth'


'


30.'What'is'the'ratio'of'the'maximum'radiation'intensity'to'the'average'radiation' intensity?'

'

(a)' Aperture'gain' (c)' Transmission'gain'

(b)' Directivity'gain' (d)' Power'gain'

31.''Good'grounding'is'important'for'

'

(a)' horizontal'antennas' (c)' vertical'antennas'

(b)' broadside'array'antennas' (d)' YagiNUda'antennas'

32.''Which'one'of'the'following'is'very'useful'as'a'multiband'HF'receiving'antenna.'

'

(a)' Parabolic'antenna' (c)' LogNperiodic'

(b)' Elementary'doublet' (d)' Square'loop'

33.''Which'one'of'the'following'is'not'a'reason'for'the'use'of'an'antenna'coupler.'

'

(a)' To'make'the'antenna'look' (b)' To'provide'the'output'amplifier'with' resistive' the'correct'load'impedance' (c)' To'discriminate'against'harmonics' (d)' To'prevent'reNradiation'of'the'local' oscillator'

34.''Which'antenna'is'not'a'wideband?'

'

(a)' Discone' (c)' Helical'

(b)' Folded'dipole' (d)' Marconi'

35.''One'of'the'following'makes'an'antenna'physically'long'but'electrically'short'

'

(a)' Adding'L'in'series' (c)' Top'loading'

(b)' Adding'C'in'series' (d)' Both'A'and'C'

36.''When'antennas'are'closed'to'the'ground,'_______'polarization'is'ideal'

' '

(a)' horizontally'polarized' (c)' circularly'polarized'

(b)' vertically'polarized' (d)' both'A'and'B'


'


37.''Any'energy'which'radiates'in'the'form'of'radio'waves,'infrared'waves,'light'waves,' xNrays,'etc.'

'

(a)' Radiant'energy' (c)' Heat'

(b)' Electromagnetic' (d)' Ultraviolet'

38.''Which'one'is'an'antenna'coupling'unit?'

'

(a)' Coupler' (c)' Lecher'wire'

(b)' Diplexer' (d)' Duplexer'

39.'''______'polarization'is'employed'in'FM'broadcasting'

'

(a)' Horizontal' (c)' Circular'

(b)' Vertical' (d)' Bidirectional'

40.''To'achieve'maximum'possible'energy'transfer'between'transmitting'and'receiving' stations'at'practical'distances,'_______'are'used.'

'

(a)' High'gain' (c)' Director'

(b)' Parabolic'reflector' (d)' secret'

41.''Impedance'transformation'between'a'balanced'and'unbalanced'impedances.'

'

(a)' Gamma'match' (c)' Decca'match'

(b)' Eslun'transformer' (d)' Match'box'

42.'''_______'is'an'instrument'that'measures'the'radiated'field'from'an'antenna.'

'

(a)' Field'strength'meter' (c)' Strength'meter'

(b)' Field'meter' (d)' Intensity'meter'

43.''This'resistance'is'a'hypothetical'concept'that'accounts'for'the'fact'that'rF'power'is' radiated'by'the'antenna.' (a)' Ohmic'resistance' (c)' Radiation'resistance' '

(b)' Resistance' (d)' None'of'these'


'


' 44.''Antenna'theory'recognizes'a'point'of'reference'called'the'_________.' (a)' HalfNwave'dipole' (c)' Isotropic'radiator'

(b)' Full'wave'dipole' (d)' Image'antenna'

' 45.'Quarter'wavelength'vertical'antenna'is'basically'a'dipole'placed'vertically,'with'the' other'half'of'the'dipole'being'the'____________.'

'

(a)' Gain' (c)' Ground'

(b)' Radials' (d)' Reflector'

46.'The'change'in'velocity'resulting'from'a'stray'capacitance'is'called'_________.'

'

(a)' End'effect' (c)' Proximity'effect'

(b)' Skin'effect' (d)' No'effect'

47.''Orientation'of'the'electric'field'signal'propagated'from'the'antenna.'

'

(a)' Directivity' (c)' Side'lobes'

(b)' Polarization' (d)' Gain'

48.''Is'not'included'in'the'group.' (a)' Slot' (c)' Helix'

(b)' Horn' (d)' Marconi'

' 49.''Impedance'for'free'space'is'_______.'

'

(a)' 120'π'' (c)' 180'π'

(b)' 30'π' (d)' None'of'these'

50.'''________'is'elective'means'to'generate'circular'polarization.' (a)' Folded'antenna' (c)' Helix'antenna' ' '

(b)' Marconi'antenna' (d)' Any'antenna'


'


51.''Is'used'to'increase'the'current'at'the'base'of'the'antenna,'and'also'to'make'the' current'distribution'more'uniform.'

'

(a)' Amplifier' (c)' Booster'

(b)' Top'loading' (d)' None'of'these'

52.''The'variation'of'the'slot'antenna'is'_________.'

'

(a)' Isotropic'antenna' (c)' Lenz'antenna'

(b)' Notch'antenna' (d)' Horn'antenna'

53.'The'property'of'an'antenna'that'causes'it'to'receive'signal'better'from'one'direction' than'from'another.'

'

(a)' Gain' (c)' Dipole'

(b)' Directivity' (d)' Reflector'

54.''A'helical'antenna'is'used'for'satellite'tracking'because'of'its'

'

(a)' Circular'polarization' (c)' Broad'bandwidth'

(b)' Maneuverability' (d)' Good'frontNtoNback'ratio'

55.''The'rhombic'antenna'is'primarily'used'for'

'

(a)' Ground'wave'propagation' (c)' Space'wave'propagation'

(b)' Skywave'propagation' (d)' Tropospheric'propagation'

56.''Calculate'the'angle'of'declination'for'an'antenna'using'a'polar'mount'at'a'latitude' of'45'degrees' (a)' 3.2'degrees' (b)' 1.3'degrees' (c)' 4.2'degrees' (d)' 6.81'degrees' 57.''The'size'of'antenna'is'inversely'proportional'to'_______.'

'

'

(a)' frequency' (c)' radiation'resistance'

(b)' power' (d)' wavelength'


'


58.''A'popular'half'–'wave'antenna'is'the'

'

(a)' Ground'plane' (c)' Collinear'

(b)' EndNfire' (d)' Dipole'

59.''______'is'the'ratio'of'the'power'radiated'by'an'antenna'to'the'sum'of'the'power' radiated'and'the'power'dissipated.'

'

(a)' radiation'resistance' (c)' antenna'efficiency'

(b)' coupling'coefficient' (d)' antenna'beamwidth'

60.''When'the'energy'is'applied'to'the'antenna'at'a'point'of'high'–'circulating'current,'it' is'called'_____.' (a)' voltageNfed'antenna' (c)' currentNfed'antenna'

(b)' powerNfed'antenna' (d)' impedanceNfed'antenna' ' 61.''The'fields'surrounding'the'antenna'do'not'collapse'their'energy'back'into'the' antenna'but'rather'radiate'it'out'in'space.'

'

(a)' induction'field' (c)' radiation'field'

(b)' near'field' (d)' magnetic'field'

62.'Zoning'is'used'with'a'dielectric'antenna'in'order'to' (a)' reduce'the'bulk'of'the'lens' (c)' permit'pinNpoint'focusing' '

(b)' increase'the'bandwidth'of'the'lens' (d)' correct'the'curvature'of'the' wavefront'from'a'horn'that'is'too' short' 63.''A'convenient'method'of'determining'antenna'impedance.'

'

(a)' Trial'and'error' (c)' Smith'chart'

(b)' Stub'matching' (d)' Reactance'circle'

64.''In'high'frequency'radio'transmission,'the'lower'the'radio'frequency'the' _______________'of'the'antenna.' (a)' Longer'the'length' (c)' Shorter'length' '

(b)' Bigger'the'diameter' (d)' Smaller'the'diameter'


'


! Wave&Propagation& 65.''Indicate'which'one'of'the'following'terms'applies'to'troposcatter'propagation' (a)' SIDs' (b)' fading' (c)' atmospheric'storms' (d)' faraday'rotation' 66.''VLF'waves'are'used'for'some'types'of'services'because' (a)' of'the'low'power'required' '

(c)' they'are'very'reliable'

(b)' the'transmitting'antennas'are'of' convenient'size' (d)' they'penetrate'the'ionosphere'easily'

67.''HighNfrequency'waves'are'

'

(a)' absorbed'by'the'F2'layer' (c)' capable'of'use'for'longNdistance' communications'on'the'moon'

(b)' reflected'by'the'D'layer' (d)' affected'by'the'solar'cycle'

68.''A'range'of'microwave'frequencies'more'easily'passed'by'the'atmosphere'than'are' the'others'is'called'a'

'

(a)' Window' (c)' gyro'frequency'range'

(b)' critical'frequency' (d)' resonance'in'the'atmosphere'

69.'Frequencies'in'the'UHF'range'normally'propagate'by'means'of'

'

(a)' ground'waves' (c)' surface'waves'

(b)' sky'waves' (d)' space'waves'

70.''Tropospheric'scatter'is'used'with'frequencies'in'the'following'range'

' '

'

(a)' HF' (c)' UHF'

(b)' VHF' (d)' VLF' '


'


71.''The'ground'wave'eventually'disappears'as'one'moves'away'from'the'transmitter' because'of'

'

(a)' interference'from'the'sky'wave' (c)' maximum'singleNhop'distance' limitation'

(b)' loss'of'line'–'of'–'sight'conditions' (d)' tilting'

72.''In'electromagnetic'waves,'polarization'means___.' (a)' the'physical'orientation'of' magnetic'field'in'space' (c)' ionization' '

(b)' the'physical'orientation'of'electric' field'in'space' (d)' the'presence'of'positive'and'negative' ions'

73.'An'electromagnetic'waves'travel'in'free'space,'only'one'of'the'following'can'happen' to'them.'

'

(a)' absorption' (c)' refraction'

(b)' attenuation' (d)' reflection'

74.'Diffraction'of'electromagnetic'waves' (a)' is'caused'by'reflections'from'the' ground' (c)' will'occur'when'the'waves'pass' through'a'large'slot' 75.''The'highest'frequencies'are'found'in'

'

(a)' XNrays' (c)' Ultraviolet'rays'

(b)' arises'only'with'spherical'wavefronts' (d)' may'occur'around'the'edge'of'a' sharp'object' (b)' Radio'waves' (d)' Radar'waves'

76.''Electromagnetic'waves'transport'

' '

'

(a)' Wavelength' (c)' Frequency'

(b)' Charge' (d)' Energy' '


'


77.''Light'of'which'the'following'colors'has'the'shortest'wavelength'

'

(a)' Red' (c)' Blue'

(b)' Yellow' (d)' Green'

78.'''The'quality'in'sound'that'corresponds'to'color'in'light'is'

'

(a)' Amplitude' (c)' Waveform'

(b)' Resonance' (d)' Pitch'

79.''When'a'beam'of'light'enters'one'medium'from'another,'a'quality'that'never' changes'is'its'

'

(a)' Direction' (c)' Speed'

(b)' Frequency' (d)' Wavelength'

80.''Relative'to'the'angle'of'incidence,'the'angle'of'refraction'

'

(a)' Is'smaller' (c)' Is'the'same'

(b)' Is'larger' (d)' Either'A'or'B'above'

81.''A'light'ray'enters'one'medium'from'another'along'the'normal.'The'angle'of' refraction'is' (a)' 0' (c)' Equal'to'the'critical'angle' 82.''Dispersion'is'the'term'used'to'describe'

' '

'

(b)' 90'degrees' (d)' Dependent'on'the'indexes'of' refraction'of'the'two'media'

(a)' The'splitting'of'white'light'into'its' (b)' The'propagation'of'light'in'straight' component'colors'in'refraction' lines' ' (c)' The'bending'of'a'beam'of'light' (d)' The'bending'of'a'beam'of'light'when' when'it'goes'from'one'medium'to' it'strikes'a'mirror' another' '


'


83.''Microwave'signals'propagate'by'way'of'the'

'

(a)' Direct'wave' (c)' Surface'wave'

(b)' Sky'wave' (d)' Standing'wave'

84.''The'ionosphere'causes'radio'signals'to'be'

'

(a)' Diffused' (c)' Refracted'

(b)' Absorbed' (d)' Reflected'

85.'Ground'wave'communications'is'most'effective'in'what'frequency'range?'

'

(a)' 300'KHz'to'3'MHz' (c)' 30'to'300'MHz'

(b)' 3'to'30'MHz' (d)' Above'300'MHz'

86.'Which'of'the'following'uses'surface'wave'propagation?' (a)' ELF' (c)' MF'

(b)' VLF' (d)' All'of'the'above'

' 87.'The'ability'of'the'ionosphere'to'reflect'a'radio'wave'back'to'the'earth'is'determined' by'

'

(a)' Operating'frequency' (c)' Angle'of'incidence'

(b)' Ion'density' (d)' All'of'the'above'

88.'A'means'beyond'the'line'of'sight'propagation'of'UHF'signals.'

'

(a)' Microwave'propagation' (c)' Troposcatter'propagation'

(b)' Space'wave'propagation' (d)' Surface'wave'propagation'

89.'Transequatorial'propagation'is'best'during'

'

(a)' Night'time' (c)' Noontime'

90.''What'is'a'doubleNhop'signal?' '

(b)' Afternoon'or'early'evening' (d)' Morning'


(a)' ground,'ionosphere,'ground'and' back'to'ionosphere' (c)' ionosphere,'ionosphere,'ground' and'ground' 91.''What'wave'is'the'same'day'or'night?'

'

(a)' sky' (c)' direct'

'


(b)' ground,'ground,'ionosphere,'and' ionosphere' (d)' ionosphere,'ground,'ionosphere'and' back'to'ground' (b)' space' (d)' ground'

92.''Polarization'named'for'_________'component'of'the'wave?'

'

(a)' static' (c)' direction'

(b)' magnetic' (d)' propagation'

93.''What'polarization'is'employed'in'an'AM'broadcasting?'

'

(a)' horizontal' (c)' transverse'

(b)' parallel' (d)' vertical'

94.''What'propagation'condition'is'usually'indicated'when'a'VHF'signal'is'received'from' a'station'500'miles'away?'

'

(a)' DNlayer'absorption' (c)' Tropospheric'ducting'

(b)' Faraday'rotation' (d)' Moonbounce'

95.''Why'does'the'radio'path'horizon'distance'exceed'the'geometric'horizon?'

'

(a)' ENlayer'skip' (c)' Auroral'skip'

(b)' DNlayer'skip' (d)' Radio'waves'may'be'bent'

96.''What'is'a'wavefront?' (a)' A'voltage'pulse'in'a'conductor' (c)' A'voltage'pulse'across'a'resistor' '

'

(b)' A'current'pulse'in'a'conductor' (d)' A'fixed'point'in'an'electromagnetic' wave'


'


97.''When'the'electric'field'is'parallel'to'the'surface'of'the'earth,'what'is'the'polarization' of'the'electromagnetic'wave?'

'

(a)' Vertical' (c)' Circular'

(b)' Horizontal' (d)' Elliptical'

98.''________'states'that'a'semirough'surface'will'reflect'as'if'it'were'a'smooth'surface' whenever'the'cosine'of'the'angle'of'incidence'is'greater'than'1/8d,'where'd'is'the'depth' of'the'surface'irregularity'and'I'is'the'wavelength'of'the'incident'wave.'

'

(a)' Rayleigh'criterion' (c)' Linear'superposition'

(b)' Huygen’s'principle' (d)' Reflection'coefficient'

99.''Energy'that'has'neither'been'radiated'into'space'nor'completely'transmitted' (a)' Modulated'waves' (c)' Standing'waves'

(b)' Captured'waves' (d)' Incident'waves'

' ' 100.'At'frequencies'below'1.5'MHz,'what'propagation'provides'the'best'coverage?'

'

(a)' Ground'wave' (c)' Sky'wave'

(b)' Space'wave' (d)' All'of'the'above'

101.''A'special'condition'which'occurs'when'the'density'of'the'lower'atmosphere'is'such' that'electromagnetic'waves'are'trapped'between'it'and'earth’s'surface'

' !

'

(a)' Duct'propagation' (c)' Space'wave'propagation' !

(b)' Sky'wave'propagation' (d)' Ground'wave'propagation'


'


Answers:&Antenna&and&Wave&Propagation&MCQs& ! 1.''(b)'

2.'(d)'

3.'(b)'

4.'(d)'

5.'(d)'

6.'(d)'

7.'(a)'

8.'(a)'

9.'(b)'

10.'(c)'

11.'(a)' 12.'(a)' 13.'(d)' 14.'(b)' 15.'(b)' 16.'(c)' 17.'(d)' 18.'(d)' 19.'(c)' 20.'(a)' 21.'(a)' 22.'(a)' 23.'(b)' 24.'(b)' 25.'(c)' 26.'(a)' 27.'(d)' 28.'(b)' 29.'(b)' 30.'(b)' 31.'(c)' 32.'(c)' 33.'(d)' 34.'(d)' 35.'(b)' 36.'(b)' 37.'(b)' 38.'(b)' 39.'(a)' 40.'(b)' 41.'(b)' 42.'(a)' 43.'(c)' 44.'(c)' 45.'(c)' 46.'(a)' 47.'(b)' 48.'(d)' 49.'(a)' 50.'(c)' 51.'(b)' 52.'(b)' 53.'(b)' 54.'(a)' 55.'(b)' 56.'(d)' 57.'(a)' 58.'(d)' 59.'(c)' 60.'(c)' 61.'(c)' 62.'(a)' 63.'(c)' 64.'(a)' 65.'(a)' 66.'(c)' 67.'(d)' 68.'(a)' 69.'(d)' 70.'(c)' 71.'(d)' 72.'(b)' 73.'(b)' 74.'(d)' 75.'(a)' 76.'(d)' 77.'(c)' 78.'(d)' 79.'(b)' 80.'(d)' 81.'(d)' 82.'(a)' 83.'(a)' 84.'(c)' 85.'(b)' 86.'(d)' 87.'(d)' 88.'(c)' 89.'(b)' 90.'(d)' 91.'(d)' 92.'(a)' 93.'(d)' 94.'(c)' 95.'(d)' 96.'(d)' 97.'(b)' 98.'(a)' 99.'(c)' 100.(a)' 101.(a)' ' '

'

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'

'

'

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Instrumentation

Contents 1 Accuracy, precision and repeatability

2

2 Electronic instruments for measuring basic parameters

2

3 Oscilloscope

2

4 Signal generators

3

5 Spectrum analyzer

4

6 Transducers

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7 Transducer construction

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8 Characteristics of transducer

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Accuracy, precision and repeatability

Accuracy T he amount of uncertainty in a measurement with respect to an absolute standard. Accuracy specifications usually contain the effect of errors due to gain and offset parameters. Offset errors can be given as a unit of measurement such as volts or ohms and are independent of the magnitude of the input signal being measured. An example might be given as ±1.0 millivolt (mV) offset error, regardless of the range or gain settings. In contrast, gain errors do depend on the magnitude of the input signal and are expressed as a percentage of the reading, such as ±0.1 percentage. Total accuracy is therefore equal to the sum of the two: ±(0.1 percentage of input + 1.0 mV ). Precision Precision describes the reproducibility of the measurement. For example, measure a steady state signal many times. In this case if the values are close together then it has a high degree of precision or repeatability. Repeatability Closeness of the agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement is called repeatability. Reproducibility Closeness of the agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement is called reproducibility.

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Electronic instruments for measuring basic parameters

Ammeters Ammeters are devices that measure current. Current in electronics is usually measured in mA which are called milliamperes, which are 1/1000s of an ampere. Basically an ammeter consists of a coil that can rotate inside a magnet, but a spring is trying to push the coil back to zero. The larger the current that flows through the coil, the larger the angle of rotation, the torque created by the current being counteracted by the return torque of the spring. Ammeters are connected in parallel with various switched resistors that can extend the range of currents that can be measured. To use that ammeter to read 10 mA full-scale it is shunted with another resistance, so that when 10 mA flows, 9 mA will flow through the shunt, and only 1 mA will flow through the meter. Similarly, to extend the range of the ammeter to 100 mA the shunt will carry 99 mA, and the meter only 1 mA. Ohmmeters Ohmmeters are basically ammeters that are connected to an internal battery, with a suitable resistance in series. Assume that the basic ammeter is ”1000 ohms per volt”, meaning that 1 mA is needed for full-scale deflection. When the external resistance that is connected to its terminals is zero, then the internal, variable, resistor in series with the ammeter is adjusted so that 1 mA will flow; that will depend on the voltage of the battery, and as the battery runs down that setting will change. The full scale point is marked as zero resistance. If an external resistance is then connected to the terminals that causes only half of the current to flow (0.5 mA in this example), then the external resistance will equal the internal resistance, and the scale is marked accordingly. When no current flows, the scale will read infinity resistance. The scale of an ohmmeter is NOT linear.Ohmmeters are usually useful in checking the short circuit and open circuit in boards. Multimeters Multimeters contain Ohmeters, Voltmeters, Ammeters and a variety of capabilities to measure other quantities. AC and DC voltages are most often measurable. Frequency of AC voltages. Multimeters also feature a continuity detector, basically an Ohmmeter with a beeper if the multimeter sees less than 100 then it beeps otherwise it is silent. Multimeters are also often able to measure capacitance and inductance. This may be achieved using a Wien bridge. A diode tester is also generally onboard, this allows one to determine the anode and cathode of an unknown diode. A LCD display is also provided for easily reading of results.

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Oscilloscope

The oscilloscope, or scope for short, is a device for drawing calibrated graphs of voltage vs time very quickly and conveniently.

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At the left side of the instrument, the CRT screen is divided into a one centimeter grid, ruled on the inside surface of the tube. Each solid line is one division for the horizontal and vertical deflection. The dotted lines are provided for pulse rise-time measurements. Moving across the panel, we come to the power switch and the CRT controls. The trace rotation and probe adjust are used only when repairing the instrument. The intensity control should be set to give a visible trace, but excessive brightness will defocus the spot and may damage the screen. Both the intensity and focus may need to be adjusted when the sweep rate is changed drastically. The beam finder is provided as an aid to setting the scope. When pushed, it reduces the deflection voltages enough that the beam will always appear on the screen. The position controls are then used to center the spot, and you should obtain a display suitable for final adjustments when the beam finder button is released.

shop.ssb cra ck.com The vertical system accepts input signals and develops appropriate deflection voltages for the CRT. Because this is a two-channel scope there are two identical sets of vertical controls, one for each trace. Voltages are applied between a grounded terminal labeled GND and either CH 1 or CH 2 for the channel desired. The coupling switch allows the input circuit to accept all signals when set at DC, or only the timevarying part when set for AC. The middle position, GND, connects the vertical amplifier input to ground, so that you can see where the zero-voltage height is on the screen. (Using the GND setting does not connect the external input terminal to ground, so your circuit will not be disturbed.) The position control allows you to place the trace on the screen as desired, for example aligning the zero-voltage position with one of the grid lines.

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Signal generators

Signal generators, also known variously as function generators, RF and microwave signal generators, etc. They are electronic devices that generate repeating or non-repeating electronic signals (in either the analog or digital domains). There are many different types of signal generators: 1. function generator : A function generator is a device which produces simple repetitive waveforms. Such devices contain an electronic oscillator, a circuit that is capable of creating a repetitive waveform. Simple function generators usually generate triangular waveform whose frequency can be controlled smoothly as well as in steps.[3] This triangular wave is used as the basis for all of its other outputs. Instrumentation

Instrumentation

Page: 4 The triangular wave is generated by repeatedly charging and discharging a capacitor from a constant current source. This produces a linearly ascending or descending voltage ramp. As the output voltage reaches upper and lower limits, the charging and discharging is reversed using a comparator, producing the linear triangle wave. By varying the current and the size of the capacitor, different frequencies may be obtained. Sawtooth waves can be produced by charging the capacitor slowly, using a current, but using a diode over the current source to discharge quickly - the polarity of the diode changes the polarity of the resulting sawtooth, i.e. slow rise and fast fall, or fast rise and slow fall. 2. Arbitrary waveform generators: It is a piece of electronic test equipment used to generate electrical waveforms. These waveforms can be either repetitive or single-shot (once only) in which case some kind of triggering source is required (internal or external). The resulting waveforms can be injected into a device under test and analyzed as they progress through it, confirming the proper operation of the device or pinpointing a fault in it. Unlike function generators, AWGs can generate any arbitrarily defined waveshape as their output. The waveform is usually defined as a series of ”waypoints” (specific voltage targets occurring at specific times along the waveform) and the AWG can either jump to those levels or use any of several methods to interpolate between those levels. • Analog signal generators based on a sine-wave oscillator were common before the inception of digital electronics, and are still used. There was a sharp distinction in purpose and design of radio-frequency and audio-frequency signal generators. • Vector signal generators are the signal generators are that capable of generating digitallymodulated radio signals that may use any of a large number of digital modulation formats • Logic signal generators also known as ’data pattern generator’ or more often ’digital pattern generator’, this type of signal generators produces logic types of signals - that is logic 1s and 0s in the form of conventional voltage levels.

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3. Special purpose signal generators: are designed for specific applications.

A pitch or audio generator is a type of signal generator optimized for use in audio and acoustics applications. Pitch generators typically include sine waves over the audio frequency range (20 Hzâ 20 kHz). Sophisticated pitch generators will also include sweep generators (a function which varies the output frequency over a range, in order to make frequency-domain measurements), multipitch generators (which output several pitches simultaneously, and are used to check for intermodulation distortion and other non-linear effects), and tone bursts (used to measure response to transients). Pitch generators are typically used in conjunction with sound level meters, when measuring the acoustics of a room or a sound reproduction system, and/or with oscilloscopes or specialized audio analyzers. A video signal generator is a device which outputs predetermined video and/or television waveforms, and other signals used to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use.

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Spectrum analyzer

A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal that a spectrum analyzer measures is electrical, however, spectral compositions of other signals, such as acoustic pressure waves and optical light waves, can be considered through the use of an appropriate transducer. Optical spectrum analyzers also exist, which use direct optical techniques such as a monochromator to make measurements. Form factor Spectrum analyzers tend to fall into four form factors: benchtop, portable, handheld and networked. • Benchtop: This form factor is useful for applications where the spectrum analyzer can be plugged into AC power, which generally means in a lab environment or production/manufacturing area.

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• Portable: This form factor is useful for any applications where the spectrum analyzer needs to be taken outside to make measurements or simply carried while in use. • Handheld: This form factor is useful for any application where the spectrum analyzer needs to be very light and small. Handheld analyzers offer a limited capability relative to larger systems. • Networked: This form factor does not include a display and these devices are designed to enable a new class of geographically-distributed spectrum monitoring and analysis applications. The key attribute is the ability to connect the analyzer to a network and monitor such devices across a network. While many spectrum analyzers have an Ethernet port for control, they typically lack efficient data transfer mechanisms and are too bulky and/or expensive to be deployed in such a distributed manner. Spectrum Analyzer Functionality • In a typical spectrum analyzer there are options to set the start, stop, and center frequency. The frequency halfway between the stop and start frequencies on a spectrum analyzer display is known as the center frequency. This is the frequency that is in the middle of the displayâ ès frequency axis. Span specifies the range between the start and stop frequencies. These two parameters allow for adjustment of the display within the frequency range of the instrument to enhance visibility of the spectrum measured. • The resolution bandwidth filter or RBW filter is the bandpass filter in the IF path. It’s the bandwidth of the RF chain before the detector (power measurement device).It determines the RF noise floor and how close two signals can be and still be resolved by the analyzer into two separate peaks. Adjusting the bandwidth of this filter allows for the discrimination of signals with closely spaced frequency components, while also changing the measured noise floor. Decreasing the bandwidth of an RBW filter decreases the measured noise floor and vice versa. This is due to higher RBW filters passing more frequency components through to the envelope detector than lower bandwidth RBW filters, therefore a higher RBW causes a higher measured noise floor.

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• Detectors are used in an attempt to adequately map the correct signal power to the appropriate frequency point on the display. There are in general three types of detectors: sample, peak, and average Sample detection : sample detection simply uses the midpoint of a given interval as the display point value. While this method does represent random noise well, it does not always capture all sinusoidal signals. Peak detection : peak detection uses the maximum measured point within a given interval as the display point value. This insures that the maximum sinusoid is measured within the interval; however, smaller sinusoids within the interval may not be measured. Also, peak detection does not give a good representation of random noise. Average detection : average detection uses all of the data points within the interval to consider the display point value. This is done by power (rms) averaging, voltage averaging, or log-power averaging. Optical spectrum analyzer An optical spectrum analyzer uses reflective and/or refractive techniques to separate out the wavelengths of light. An electro-optical detector is used to measure the intensity of the light, which is then normally displayed on a screen in a similar manner to a radio- or audio-frequency spectrum analyzer. The input to an optical spectrum analyzer may be simply via an aperture in the instrument’s case, an optical fiber or an optical connector to which a fiber-optic cable can be attached.

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Transducers

A transducer is any device that converts one form of energy into another. Piezoelectric effect is a phenomenon of physics characterized by the conversion of pressure energy into electrical energy. Converse effect is the production of mechanical (ultrasound) energy when an electrical impulse is applied to certain crystals or composite materials. Types of crystals: Instrumentation

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• Isotropic refers to the characteristic of a substance possessing molecular symmetry, or equal physical properties, along all axes. • Anisotropic crystals do not have centers of symmetry, so their properties, and response to external forces, are different in different directions. When a voltage is applied to an anisotropic piezoelectric crystal, the element will contract or expand depending on the polarity of the voltage. When such a crystal is compressed by a pressure wave such as a returning echo, a voltage will be produced across the piezoelectric element.

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Transducer construction

• Damping material: The damping block, which usually is made of an epoxy-like material, is glued to the inner surface of the crystal. It serves to absorb the ”reverse” ultrasound waves that are transmitted to the back of the crystal.

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• Insulating ring: It is known as a sidewall acoustic insulator, this part of a transducer is made of the same material as the damping block. It serves primarily to absorb energy generated from the sides of the crystal. • Tuning coil The crystal is a capacitative device forming part of the pulser and receiver circuits. (Capacitors are electronic devices that can store electrical charges.) The tuning coil serves to offset the capacitative effect of the crystal by removing residual electrical charges. Just as defogging the bathroom mirror improves the ”efficiency” of the mirror in reflecting your morning face, the tuning coil, by ”dusting off” excess electrical charges, improves the transmitting and receiving functions of the transducer. • Electric shield: The electric shield is an isolation barrier that serves to eliminate unwanted, stray signals known as ”noise’. It does this by detecting, isolating and sending them to ground. NOISE is any unwanted vibration that interferes with the efficient production of a sonographic image. • Electric connectors: These connectors serve to electrically link the transducer to the ultrasound instrument. It is through these connectors that the electrical impulse that rings the crystal is delivered and the returning echoes are received. Generally they are a pair of very thin wires attached to each crystal. • Matching layers: The primary objective in designing transducers for diagnostic ultrasound imaging systems includes achieving the highest sensitivity, penetration, optimal focal characteristics, and best possible resolution all at low acoustic power levels. Quality factor The Q-factor is a unitless number that represents the ability of the transducer to emit a ”clean” or ”quality” ultrasound frequency. Q ≠ f actor =

Instrumentation

resonantf requency(M Hz) f requencybandwidth(M Hz)

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Characteristics of transducer • accuracy: It is the conformity of an indicated value to an accepted standard, or true value. It defines the limit the errors will not exceed when the instrument is used under stated operating conditions. • resolution: The smallest difference between measured values that can be discriminated. For example, it corresponds to the last stable figure on a digital display. • calibration: The degree to which an instrument is known to conform to an accepted standard is termed as its calibration. Both the accuracy and reliability of an instrument depends on its construction and on how well it holds its calibration. • repeatability: The repeatability is the agreement among a number of consecutive measurements of the output for the same value of the input â under the same operating conditions and when approached from the same direction. • reproducibility: It is known as the agreement among repeated measurements of the output for the same value of the input over a period of time under the same operating conditions and when approached from either direction. • hysteresis: The effect in which a measured value differs for the same value of the input if the input is applied in an increasing direction versus a decreasing direction, is called hysteresis • linearity: For successive equal increments of the input, the linearity is the deviation of the plotted transducer output from a straight line. This is often defined in terms of a percentage of the maximum or full scale output. • sensitivity: It is the ratio of the change in the magnitude of the output to the change in the input which caused it after the steady state has been reached.

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• noise: Noise (in the transducer) consists of signals generated within the transducer, independent of the input signal, which contribute to the output. Such signals may be intrinsic to the transducer (for example, due to thermal fluctuations of carrier concentrations in a semiconductor), or be generated by interaction with the environment (for example, by RF pickup). • threshold: The minimum value for which a noticeable or measurable response is produced. A relevant consideration especially for active elements (as opposed to passive). • noise floor: The lower limit of what can be measured set by the noise levels of the transducer.

• saturation level: The maximum input level before significant non-linearities in the output appear.

• maximum input: The highest input signal which gives a calibrated output. This level can be set due to saturation, damage to the transducer, safety, output signal degradation. • dynamic range: The ratio of the maximum input signal to the noise floor or threshold. Often reported in decibels: DR = 10log10

max min

• response time (tr ) it is the time interval between a change in the measured quantity and the time an instrument reads a new equilibrium value. • dead time (td ): time during which a new signal or variation in a signal cannot be detected due to some physical characteristic of the system or the transducer • rise time (tr ): the time taken by the instrument to respond to a step change in a measured quantity, often defined as the time taken to change from 10 • settling time (ts ): the time required for an instrument to attain a stable reading within a stated percentage of its equilibrium output, often taken to be the time to the first minimum of the oscillation.

Instrumentation

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Instrumentation'MCQs'

Instrumentation,MCQs, ' 1.'The'use'of'_____'instruments'is'merely'confined'within'laboratories'as'standardizing' instruments.' (a)' 'absolute' (b)' indicating' (c)' recording' (d)' integrating' ' 2.'Which'of'the'following'instruments'indicate'the'instantaneous'value'of'the'electrical' quantity' being'measured'at'the'time'at'which'it'is'being'measured'?' (a)' Absolute'instruments' (b)' Indicating'instruments' (c)' Recording'instruments' (d)' Integrating'instruments' ' 3.'_____'instruments'are'those'which'measure'the'total'quantity'of'electricity'delivered' in'a' particular'time.' (a)' Absolute' (b)' Indicating' (c)' Recording' (d)' Integrating' ' 4.'Which'of'the'following'are'integrating'instruments?' (a)' Ammeters' (b)' Voltmeters' (c)' Wattmeters' (d)' AmpereMhour'and'wattMhour'meters' ' 5.'Resistances'can'be'measured'with'the'help'of' (a)' wattmeters' (b)' voltmeters' (c)' ammeters' (d)' ohmmeters'and'resistance'bridges' ' 6'According'to'application,'instruments'are'classified'as' (a)' switch'board' (b)' portable' (c)' both'(a)'and'(b)' ' ' ' 7.'Which'of'the'following'essential'features'is'possessed'by'an'indicating'instrument?' (a)' Deflecting'device' (b)' Controlling'device' (c)' 'Damping'device' (d)' )'All'of'the'above' ' 8.'A'_____'device'prevents'the'oscillation'of'the'moving'system'and'enables'the'latter' to' reach'its'final'position'quickly' (a)' deflecting' (b)' controlling' (c)' damping' (d)' any'of'the'above' '


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' 9.'The'spring'material'used'in'a'spring'control'device'should'have'the'following' property.' (a)' Should'be'nonMmagnetic' (b)' Most'be'of'low'temperature'coM efficient' (c)' Should'have'low'specific' (d)' 'All'of'the'above' resistance' ' 10.'Which'of'the'following'properties'a'damping'oil'must'possess'?' (a)' 'Must'be'a'good'insulator' (b)' Should'be'nonMevaporating' (c)' Should'not'have'corrosive'action' (d)' All'of'the'above' upon'the'metal'of'the'vane' ' ' 11.'A'movingMcoil'permanentMmagnet'instrument'can'be'used'as'_____'by'using'a'low' resistance'shunt.' (a)' ammeter' (b)' voltmeter' (c)' 'fluxMmeter' (d)' ballistic'galvanometer' ' 12.'A'movingMcoil'permanentMmagnet'instrument'can'be'used'as'fluxMmeter' (a)' by'using'a'low'resistance'shunt' (b)' by'using'a'high'series'resistance' (c)' by'eliminating'the'control'springs' (d)' by'making'control'springs'of'large' moment'of'inertia' ' 13.'Which'of'the'following'devices'may'be'used'for'extending'the'range'of'instruments?' (a)' 'Shunts' (b)' Multipliers' (c)' Current'transformers' (d)' All'of'the'above' ' 14.'An'induction'meter'can'handle'current'upto' (a)' 10'A' (b)' 30'A' (c)' 60'A' (d)' 100'A' ' 15.'For'handling'greater'currents'induction'wattmeters'are'used'in'conjunction'with' (a)' potential'transformers' (b)' current'transformers' (c)' power'transformers' (d)' either'of'the'above' ' 16.'Induction'type'single'phase'energy'meters'measure'electric'energy'in' (a)' kW' (b)' Wh' (c)' kWh' (d)' VAR' ' 17.'Most'common'form'of'A.C.'meters'met'with'in'every'day'domestic'and'industrial' '


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Installations'are' (a)' mercury'motor'meters' (b)' 'commutator'motor'meters' (c)' induction'type'single'phase' (d)' all'of'the'above' energy'meters' ' 18.'Which'of'the'following'meters'are'not'used'on'D.C.'circuits' (a)' Mercury'motor'meters' (b)' Commutator'motor'meters' (c)' Induction'meters' (d)' None'of'the'above' ' 19.'Which'of'the'following'is'an'essential'part'of'a'motor'meter'?' (a)' An'operating'torque'system' (b)' A'braking'device' (c)' Revolution'registering'device' (d)' All'of'the'above' ' 20.'A'potentiometer'may'be'used'for' (a)' measurement'of'resistance' (b)' measurement'of'current' (c)' calibration'of'ammeter' (d)' all'of'the'above' ' 21__________'is'an'instrument'which'measures'the'insulation'resistance'of'an'electric' circuit'relative'to' earth'and'one'another,' (a)' Tangent'galvanometer' (b)' Meggar' (c)' Current'transformer' (d)' None'of'the'above' ' '22.'The'household'energy'meter'is' (a)' an'indicating'instrument' (b)' a'recording'instrument' (c)' an'integrating'instrument' (d)' none'of'the'above' ' 23.'The'pointer'of'an'indicating'instrument'should'be' (a)' very'light' (b)' very'heavy' (c)' either'(a)'or'(b)' (d)' neither'(a)'nor'(b)' ' 24.The'chemical'effect'of'current'is'used'in' (a)' D.C.'ammeter'hour'meter' (b)' D.C.'ammeter' (c)' D.C.'energy'meter' (d)' none'of'the'above' ' 25.'In'majority'of'instruments'damping'is'provided'by' (a)' fluid'friction' (b)' spring' (c)' eddy'currents' (d)' all'of'the'above' ' 26.'An'ammeter'is'a' '


(a)' secondary'instrument' (c)' recording'instrument'

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(b)' absolute'instrument' (d)' integrating'instrument'

' 27.'In'a'portable'instrument,'the'controlling'torque'is'provided'by' (a)' spring' (b)' gravity' (c)' eddy'currents' (d)' all'of'the'above' ' 28.'The'disc'of'an'instrument'using'eddy'current'damping'should'be'of' (a)' conducting'and'magnetic'material' (b)' nonMconducting'and'magnetic' material' (c)' conducting'and'nonMmagnetic' (d)' none'of'the'above' material' ' 29.'The'switch'board'instruments' (a)' should'be'mounted'in'vertical' (b)' should'be'mounted'in'horizontal' position' position' (c)' either'(a)'or'(b)' (d)' neither'(a)'nor'(b)' ' 30.'The'function'of'shunt'in'an'ammeter'is'to' (a)' by'pass'the'current' (b)' increase'the'sensitivity'of'the' ammeter' (c)' increase'the'resistance'of' (d)' none'of'the'above' ammeter' ' 31.'The'multiplier'and'the'meter'coil'in'a'voltmeter'are'in' (a)' series' (b)' parallel' (c)' seriesMparallel' (d)' none'of'the'above' ' 32.'A'moving'iron'instrument'can'be'used'for' (a)' D.C.'only' (b)' A.C.'only' (c)' both'D.C.'and'A.C.' (d)' ' ' 33.'The'scale'of'a'rectifier'instrument'is' (a)' linear' (b)' nonMlinear' (c)' either'(a)'or'(b)' (d)' neither'(a)'nor'(b)' ' '34.'For'measuring'current'at'high'frequency'we'should'use' (a)' moving'iron'instrument' (b)' electrostatic'instrument' (c)' thermocouple'instrument' (d)' none'of'the'above' ' '


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35.'The'resistance'in'the'circuit'of'the'moving'coil'of'a'dynamometer'wattmeter'should' be' (a)' 'almost'zero' (b)' low' (c)' high' (d)' none'of'the'above' ' 36.'A'dynamometer'wattmeter'can'be'used'for' ' (a)' 'both'D.C.'and'A.C.' (b)' D.C.'only' (c)' A.C.'only' (d)' any'of'the'above' ' 37.'An'induction'wattmeter'can'be'used'for' (a)' both'D.C.'and'A.C.' (b)' D.C.'only' (c)' A.C.'only' (d)' any'of'the'above' ' 38.'The'pressure'coil'of'a'wattmeter'should'be'connected'on'the'supply'side'of'the' current'coil' When' (a)' load'impedance'is'high' (b)' load'impedance'is'low' (c)' supply'voltage'is'low' (d)' none'of'the'above' ' 39.'In'a'low'power'factor'wattmeter'the'pressure'coil'is'connected' (a)' to'the'supply'side'of'the'current' (b)' to'the'load'side'of'the'current'coil' coil' (c)' in'any'of'the'two'meters'at' (d)' none'of'the'above' connection' ' 40.'In'a'low'power'factor'wattmeter'the'compensating'coil'is'connected' (a)' in'series'with'current'coil' (b)' in'parallel'with'current'coil' (c)' in'series'with'pressure'coil' (d)' in'parallel'with'pressure'coil' ' 41.'In'a'3Mphase'power'measurement'by'two'wattmeter'method,'both'the'watt'meters' had' identical'readings.'The'power'factor'of'the'load'was' (a)' unity' (b)' 0.8'lagging' (c)' 0.8'leading' (d)' zero' ' 42.'In'a'3Mphase'power'measurement'by'two'wattmeter'method'the'reading'of'one'of' the' wattmeter'was'zero.'The'power'factor'of'the'load'must'be' (a)' unity' (b)' 0.5' (c)' 0.3' (d)' zero' '


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' 43.'The'adjustment'of'position'of'shading'bands,'in'an'energy'meter'is'done'to'provide' (a)' friction'compensation' (b)' creep'compensation' (c)' braking'torque' (d)' 'none'of'the'above' ' 44.'An'ohmmeter'is'a' (a)' moving'iron'instrument' (b)' moving'coil'instrument' (c)' dynamometer'instrument' (d)' none'of'the'above' ' 45.'When'a'capacitor'was'connected'to'the'terminal'of'ohmmeter,'the'pointer'indicated' a'low' resistance'initially'and'then'slowly'came'to'infinity'position.'This'shows'that'capacitor'is' (a)' shortMcircuited' (b)' all'right' (c)' faulty' (d)' ' ' 46.'For'measuring'a'very'high'resistance'we'should'use' (a)' Kelvin's'double'bridge' (b)' Wheat'stone'bridge' (c)' Meggar' (d)' None'of'the'above' ' 47.'The'electrical'power'to'a'meggar'is'provided'by' (a)' battery' (b)' permanent'magnet'D.C.'generator' (c)' AC.'generator' (d)' any'of'the'above' ' 48.'In'a'meggar'controlling'torque'is'provided'by' (a)' spring' (b)' gravity' (c)' coil' (d)' 'eddy'current' ' 49.'The'operating'voltage'of'a'meggar'is'about' (a)' 6'V' (b)' 12'V' (c)' 40'V' (d)' 100'V' ' 50.'Murray'loop'test'can'be'used'for'location'of' (a)' ground'fault'on'a'cable(b)'short' (b)' both'the'ground'fault'and'the'shortM circuit'fault'on'a'cable' circuit'fault' (c)' none'of'the'above' (d)' ' ' 51.'Which'of'the'following'devices'should'be'used'for'accurate'measurement'of'low' D.C.' voltage'?' (a)' Small'range'moving'coil'voltmeter' (b)' D.C.'potentiometer' '


(c)' Small'range'thermocouple' voltmeter'

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(d)' None'of'the'above'

' 52.'It'is'required'to'measure'the'true'open'circuit'e.m.f.'of'a'battery.'The'best'device'is' (a)' D.C.'voltmeter' (b)' Ammeter'and'a'known'resistance' (c)' D.C.'potentiometer' (d)' 'None'of'the'above' ' 53.'A'voltage'of'about'200'V'can'be'measured' (a)' directly'by'a'D.C.'potentiometer' (b)' a'D.C.'potentiometer'in'conjunction' with'a'volt'ratio'box' (c)' a'D.C.'potentiometer'in' (d)' none'of'the'above' conjunction'with'a'known' resistance' ' 54.'A'direct'current'can'be'measured'by' (a)' a'D.C.'potentiometer'directly' (b)' a'D.C.'potentiometer'in'conjunction' with'a'standard'resistance' (c)' a'D.C.'potentiometer'in' (d)' none'of'the'above' conjunction'with'a'volt'ratio'box' ' ' 55.'To'measure'a'resistance'with'the'help'of'a'potentiometer'it'is' (a)' necessary'to'standardise'the' (b)' not'necessary'to'standardise'the' potentiometer' potentiometer' (c)' necessary'to'use'a'volt'ratio'box' (d)' none'of'the'above' in'conjunction'with'the' potentiometer' ' 56.'A'phase'shifting'transformer'is'used'in'conjunction'with' (a)' D.C.'potentiometer' (b)' Drysdale'potentiometer' (c)' A.C.'coMordinate'potentiometer' (d)' Crompton'potentiometer' ' 57.'Basically'a'potentiometer'is'a'device'for' (a)' comparing'two'voltages' (b)' measuring'a'current' (c)' comparing'two'currents' (d)' measuring'a'voltage' ' 58.'In'order'to'achieve'high'accuracy,'the'slide'wire'of'a'potentiometer'should'be' (a)' as'long'as'possible' (b)' as'short'as'possible' (c)' neither'too'small'not'too'large' (d)' very'thick' ' ' '


'


' ' ' 59.'To'measure'an'A.'C.'voltage'by'using'an'A.C.'potentiometer,'it'is'desirable'that'the' supply' for'the'potentiometer'in'taken' (a)' from'a'source'which'is'not'the' (b)' from'a'battery' same'as'the'unknown'voltage' (c)' from'the'same'source'as'the' (d)' any'of'the'above' unknown'voltage' ' 60.'The'stator'of'phase'shifting'transformer'for'use'in'conjunction'with'an'A.C.' potentiometer' usually'has'a' (a)' singleMphase'winding' (b)' twoMphase'winding' (c)' )'threeMphase'winding' (d)' any'of'the'above' ' 61.'In'an'AC.'coMordinate'potentiometer,'the'currents'in'the'phase'and'quadrature' Potentiometer'are'adjusted'to'be' (a)' out'of'phase'by'90°' (b)' out'of'phase'by'60°' (c)' out'of'phase'by'30°' (d)' out'of'phase'by'0°' ' 62.'A'universal'RLC'bridge'uses' (a)' 'Maxwell' bridge' configuration' for' (b)' Maxwell'Wein'bridge'for' measurement' of' inductance' and' measurement'of'inductance'and' De' Santas' bridge' for' modified'De'Santy's'bridge'for' measurement'of'capacitance' measurement'of'capacitance' ' (c)' Maxwell'Wein'bridge'for' (d)' Any'of'the'above' measurement'of'inductance'and' Wein'bridge'for'measurement'of' capacitance' ' 63.'For'measurements'on'high'voltage'capacitors,'the'suitable'bridge'is' (a)' Wein'bridge' (b)' Modified'De'Santy's'bridge' (c)' Schering'bridge' (d)' None'of'the'above' ' 64.'In'an'Anderson'bridge,'the'unknown'inductance'is'measured'in'terms'of' (a)' known'inductance'and'resistance' (b)' 'known'capacitance'and'resistance' (c)' known'resistance' (d)' known'inductance' '


'


' 65.'Wagner'earthing'device'is'used'to'eliminate'errors'due'to' (a)' electrostatic'coupling' (b)' electromagnetic'coupling' (c)' both'(a)'and'(b)' (d)' none'of'the'above' ' 66.'For'measurement'of'mutual'inductance'we'can'use' (a)' Anderson'bridge' (b)' Maxwell's'bridge' (c)' Heaviside'bridge' (d)' Any'of'the'above' ' 67.'For'measurement'of'inductance'having'high'value,'we'should'use' (a)' Maxwell's'bridge' (b)' Maxwell'Wein'bridge' (c)' Hay's'bridge' (d)' Any'of'the'above' ' 68.'If'the'current'in'a'capacitor'leads'the'voltage'by'80°,'the'loss'angle'of'the'capacitor'is' (a)' 10°' (b)' 80°' (c)' 120°' (d)' 170°' ' ' 69.'In'a'Schering'bridge'the'potential'of'the'detector'above'earth'potential'is' (a)' a'few'volts'only' (b)' 1'kV' (c)' 5'kV' (d)' 10'kV' ' 70.'To'avoid'the'effect'of'stray'magnetic'field'in'A.C.'bridges'we'can'use' (a)' magnetic'screening' (b)' Wagner'earthing'device' (c)' wave'filters' (d)' any'of'the'above' ' 71.'If'an'inductance'is'connected'in'one'arm'of'bridge'and'resistances'in'the'remaining' three' Arms' (a)' the'bridge'can'always'be'balanced' (b)' the'bridge'cannot'be'balanced' (c)' the'bridge'can'be'balanced'if'the' ' ' resistances'have'some'specific' values' ' 72.'A'power'factor'meter'has' (a)' one'current'circuit'and'two' (b)' one'current'circuit'and'one'pressure' pressure'circuits' circuit' (c)' two'current'circuits'and'one' (d)' none'of'the'above' pressure'circuit' ' '


'


73.'The'two'pressure'coils'of'a'single'phase'power'factor'meter'have' (a)' the'same'dimensions'and'the' (b)' the'same'dimension'but'different' same'number'of'turns' number'of'turns' (c)' the'same'number'of'turns'but' (d)' none'of'the'above' different'dimensions' ' 74.'In'a'single'phase'power'factor'meter'the'phase'difference'between'the'currents'in' the'two' pressure'coils'is' (a)' exactly'0°' (b)' approximately'0°' (c)' exactly'90°' (d)' approximately'90°' ' 75.'In'a'dynamometer'3Mphase'power'factor'meter,'the'planes'of'the'two'moving'coils' are'at' (a)' 0°' (b)' 60°' (c)' 90°' (d)' 120°' ' 76.'In'a'vibrating'reed'frequency'meter'the'natural'frequencies'of'two'adjacent'reeds' have'a' difference'of' (a)' 0.1'Hz' (b)' 0.25'Hz' (c)' 0.5'Hz' (d)' 1.5'Hz' ' 77.'In'a'Weston'frequency'meter,'the'magnetic'axes'of'the'two'fixed'coils'are' (a)' parallel' (b)' perpendicular' (c)' inclined'at'60°' (d)' inclined'at'120°' ' 78.'A'Weston'frequency'meter'is' (a)' moving'coil'instrument' (b)' moving'iron'instrument' (c)' dynamometer'instrument' (d)' none'of'the'above' ' 79.'A'Weston'synchronoscope'is'a' (a)' moving'coil'instrument' (b)' moving'iron'instrument' (c)' dynamometer'instrument' (d)' none'of'the'above' ' 80.'In'a'Weston'synchronoscope,'the'fixed'coils'are'connected'across' (a)' busMbars' (b)' 'incoming'alternator' (c)' a'lamp' (d)' none'of'the'above' ' 81.'In'Weston'synchronoscope'the'moving'coil'is'connected'across' '


(a)' busMbars' (c)' fixed'coils'

'


(b)' incoming'alternator' (d)' any'of'the'above'

' 82.'The'power'factor'of'a'single'phase'load'can'be'calculated'if'the'instruments' available'are' (a)' one'voltmeter'and'one'ammeter' (b)' one'voltmeter,'one'ammeter'and'one' wattmeter' (c)' one'voltmeter,'one'ammeter'and' (d)' any'of'the'above' one'energy'meter' ' 83.'The'desirable'static'characteristics'of'a'measuring'system'are' (a)' accuracy'and'reproducibility' (b)' accuracy,'sensitivity'and' reproducibility' (c)' drift'and'dead'zone' (d)' static'error' ' 84.'The'ratio'of'maximum'displacement'deviation'to'full'scale'deviation'of'the' instrument'is' Called' (a)' static'sensitivity' (b)' dynamic'deviation' (c)' 'linearity' (d)' precision'or'accuracy' ' 85.'Systematic'errors'are' (a)' instrumental'errors' (b)' environmental'errors' (c)' observational'errors' (d)' all'of'the'above' ' 86.'Standard'resistor'is'made'from' (a)' platinum' (b)' maganin' (c)' silver' (d)' nichrome' ' 87.'Commonly'used'standard'capacitor'is' (a)' spherical'type' (b)' concentric'cylindrical'type' (c)' electrostatic'type' (d)' multilayer'parallel'plate'type' ' 88.'Operating'torques'in'analogue'instruments'are' (a)' deflecting'and'control' (b)' deflecting'and'damping' (c)' deflecting,'control'and'damping' (d)' vibration'and'balancing' ' 89.'Commonly'used'instruments'in'power'system'measurement'are' (a)' induction' (b)' moving'coil'or'iron' (c)' rectifier' (d)' electrostatic' '


'


' 90.'Damping'of'the'Ballistic'galvanometer'is'made'small'to' (a)' get'first'deflection'large' (b)' make'the'system'oscillatory' (c)' make'the'system'critically' (d)' get'minimum'overshoot' damped' ' 91.'If'an'instrument'has'cramped'scale'for'larger'values,'then'it'follows' (a)' square'law' (b)' logarithmic'law' (c)' uniform'law' (d)' none'of'the'above' ' ' 92.'Volt'box'is'a'component'to' (a)' extend'voltage'range' (b)' measure'voltage' (c)' compare'voltage'in'a'box' (d)' none'of'the'above' ' 93.'E.m.f.'of'a'Weston'cell'is'accurately'measured'by' (a)' electrostatic'voltmeter' (b)' hot'wire'voltmeter' (c)' isothermal'voltmeter' (d)' )'electrodynamic'voltmeter' ' 94.'A'sensitive'galvanometer'produces'large'deflection'for'a' (a)' small'value'of'current' (b)' large'value'of'current' (c)' large'value'of'power' (d)' large'value'of'voltage' ' 95.'A'multirange'instrument'has' (a)' multiple'shunt'or'series' (b)' multicoil'arrangement' resistances'inside'the'meter' (c)' variable'turns'of'coil' (d)' multi'range'meters'inside'the' measurement'system' ' 96.'The'rectifier'instrument'is'not'free'from' (a)' temperature'error' (b)' wave'shape'error' (c)' frequency'error' (d)' all'of'the'above' ' 97.'Alternating'current'is'measured'by' (a)' induction'ammeter' (b)' permanent'magnet'type'ammeter' (c)' electrostatic'ammeter' (d)' moving'iron'repulsion'type'voltmeter' ' 98.'Most'sensitive'galvanometer'is' (a)' elastic'galvanometer' (b)' vibration'galvanometer' (c)' Duddlb'galvanometer' (d)' spot'ballistic'galvanometer' '


'


' 99.'Instrument'transformers'are' (a)' potential'transformers' (b)' current'transformers' (c)' both'(a)'and'(b)' (d)' power'transformers' ' 100.'An'instrument'transformer'is'used'to'extend'the'range'of' (a)' induction'instrument' (b)' 'electrostatic'instrument' (c)' moving'coil'instrument' (d)' any'of'the'above' ' 101.'Wattmeter'cannot'be'designed'on'the'principle'of' (a)' electrostatic'instrument' (b)' thermocouple'instrument' (c)' moving'iron'instrument' (d)' electrodynamic'instrument' ' 102.'In'an'energy'meter'braking'torque'is'produced'to' (a)' safe'guard'it'against'creep' (b)' brake'the'instrument' (c)' bring'energy'meter'to'stand'still' (d)' maintain'steady'speed'and'equal'to' driving'torque' ' 103.'Various'adjustments'in'an'energy'meter'include' (a)' 'light'load'or'friction' (b)' lag'and'creep' (c)' overload'and'voltage' (d)' all'of'the'above' compensation' ' ' 104.'The'power'of'a'nMphase'circuit'can'be'measured'by'using'a'minimum'of' (a)' (n'M'1)'wattmeter'elements' (b)' n'wattmeter'elements' (c)' (n'+'1)'wattmeter'elements' (d)' 2n'wattmeter'elements' ' 105.'Two'holes'in'the'disc'of'energy'meter'are'drilled'at'the'opposite'sides'of'the' spindle'to' (a)' improve'its'ventilation' (b)' eliminate'creeping'at'no'load' (c)' increase'its'deflecting'torque' (d)' increase'its'braking'torque' ' 106.'Which'of'the'following'is'measured'by'using'a'vector'voltmeter?' (a)' Amplifier'gain'and'phase'shift' (b)' 'Filler'transfer'functions' (c)' Complex'insertion'loss' (d)' All'of'the'above' ' 107.'The'principle'on'which'vector'voltmeter'is'based'is' (a)' that'it'works'on'the'principle'of' (b)' that'it'measures'the'response'of' complex'variation' linear'ramp'voltage' '


'


(c)' same'as'digital'meter'

(d)' that'it'measures'the'amplitude'of'a' single'at'two'points'and'at'the'same' time'measures'their' phase'difference' 108.'To'measure'radio'frequency,'the'suitable'frequency'meter'is' (a)' Weston'frequency'meter' (b)' reed'vibrator'frequency'meter' (c)' 'heterodyne'frequency'meter' (d)' electrical'resonance'frequency'meter' ' ' ' Answers:(Instrumentation(MCQs( ( 1.(((a)(

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Network Theory Design Contents 1 Thevenin’s Theorem

2

2 Norton’s theorem

3

3 Reciprocity theorem

5

4 Superposition theorem

5

5 Compensation theorem

6

6 Millers theorem

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7 Tellegen’s theorem

8

8 Maximum power transfer theorems 8.1 Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 9

9

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Response of First-order circuit

10

10 Response of Second-order circuit

13

11 Two port parameters

14

12 Application of Laplace transform

17

13 Inverse Laplace transform

18

14 Application of Fourier series

19

1

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1

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Thevenin’s Theorem 1. Given any linear circuit, rearrange it in the form of two networks, (say) A and B, connected by two wires. Network A is the network to be simplified; B will be left untouched. 2. Disconnect network B. Define a voltage voc as the voltage now appearing across the terminals of network A. 3. Turn off or ”zero out” every independent source in network A to form an inactive network. Leave dependent sources unchanged. 4. Connect an independent voltage source with value vo c in series with the inactive network. Do not complete the circuit; leave the two terminals disconnected. 5. Connect network B to the terminals of the new network A. All currents and voltages in B will remain unchanged.

Example: Consider the circuit shown in Figure shown below. Determine the Thevenin equivalent of network A.

Solution:

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• Treat the 12 V source and the 3 resistor as a practical voltage source and replace it with a practical current source consisting of a 4 A source in parallel with 3 3 .

• The parallel resistances are then combined into 2

• The practical current source that results is transformed back into a practical voltage source


Network Theory Design

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• The final result is shown as

Note: • The only restriction that we must impose on A or B is that all dependent sources in A have their control variables in A, and similarly for B.

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• No restrictions are imposed on the complexity of A or B; either one may contain any combination of independent voltage or current sources, linear dependent voltage or current sources, resistors, or any other circuit elements which are linear. • The dead network A can be represented by a single equivalent resistance RT H , which we will call the Thevenin equivalent resistance. This holds true whether or not dependent sources exist in the inactive A network, an idea we will explore shortly. • A Thevenin equivalent consists of two components: a voltage source in series with a resistance. Either may be zero, although this is not usually the case.

2

Norton’s theorem 1. Given any linear circuit, rearrange it in the form of two networks, A and B, connected by two wires. Network A is the network to be simplified; B will be left untouched. As before, if either network contains a dependent source, its controlling variable must be in the same network. 2. Disconnect network B, and short the terminals of A. Define a current isc as the current now flowing through the shorted terminals of network A. 3. Turn off or ”zero out” every independent source in network A to form an inactive network. Leave dependent sources unchanged. 4. Connect an independent current source with value isc in parallel with the inactive network. 5. Connect network B to the terminals of the new network A. All currents and voltages in B will remain unchanged.



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Example: Find the Norton equivalent circuits for the network faced by the 1K

resistor in figure below

From the wording of the problem statement, network B is the 1k resistor, so network A is everything else. Choosing to find the Thevenin equivalent of network A first, we apply superposition, noting that no current flows through the 3k resistor once network B is disconnected. With the current source set to zero, Voc |4v = . With the voltage source set to zero, Voc |2mA = (0.002)(2000) = 4V. T hus, Voc = 4 + 4 = 8V.

To find RT H , set both sources to zero as shown below

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By inspection, RT H = 2k + 3k = 5k . The complete Thevenin equivalent, with network B reconnected, is shown in figure below

The Norton equivalent is found by a simple source transformation of the Thevenin equivalent, resulting 8 in a current source of 5000 = 1.6mA in parallel with a 5k resistor.

Removing the 1k

resistor and shorting the terminals of network A, we find Is c as shown in figure



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Isc = Isc |4V +Isc |2mA =

3

4 2 + (2) = 0.8 + 0.8 = 1.6mA 2+3 2+3

Reciprocity theorem

Reciprocity theorem states that if an emf E in one branch of a reciprocal network produces a current I in another, then if the emf E is moved from the first to the second branch, it will cause the same current in the first branch, where the emf has been replaced by a short circuit.

4

Superposition theorem 1. Select one of the independent sources. Set all other independent sources to zero. This means voltage sources are replaced with short circuits and current sources are replaced with open circuits. Leave dependent sources in the circuit. 2. Relabel voltages and currents using suitable notation (e.g., v, i2 ). Be sure to relabel controlling variables of dependent sources to avoid confusion.

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3. Analyze the simplified circuit to find the desired currents and/or voltages.

4. Repeat steps 1 through 3 until each independent source has been considered. 5. Add the partial currents and/or voltages obtained from the separate analyses. Pay careful attention to voltage signs and current directions when summing. 6. Do not add power quantities. If power quantities are required, calculate only after partial voltages and/or currents have been summed. Example: Use the superposition principle to determine the value of ix .

Solution: First open-circuit the 3 A source.



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The single mesh equation is â ä10 + 2ix + ix + 2ix = 0 so that, iÕx = 2A Next, short-circuit the 10 V source

Single node equation

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v” v” ≠ 2i”x + =3 2 1 and relate the dependent-source-controlling quantity to v”: v” = 2(≠i”x ) Solving, we find ix = ≠0.6A

and thus,

ix = ix + ix = 2 + (≠0.6) = 1.4A

5

Compensation theorem

According to this theorem, any resistance in a network may be replaced by a voltage source that has zero internal resistance and a voltage equal to the voltage drop across the replace resistance due to the current which was flowing through it. This imaginary voltage source is directed opposite to the voltage source of that replaced resistance. Think about a resistive branch of any complex network that’s resistance value is R. Let’s assume current I is flowing through that resistor R and voltage drops due to this current across the resistor is V = I.R. According to compensation theorem, this resistor can be replaced by a voltage source that’s generated voltage will be V ( = IR) and will be directed against the direction of network voltage or direction of current I.



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Here in the network for 16 V source, all the currents flowing through the different resistive branches are shown in the first figure. The current through the right most branch in the figure is 2A and its resistance is 2 . If this right most branch of the network is replaced by a voltage source V = 2 ◊ 2A = 4V directed as shown in the second figure, then current through the other branches of the network will remain the same as shown in the second figure.

6

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Millers theorem

The Miller theorem establishes that in a linear circuit, if there exists a branch with impedance Z, connecting two nodes with nodal voltages V1 and V2, we can replace this branch by two branches connecting the corresponding nodes to ground by impedances respectively Z/(1 - K) and KZ/(K - 1), where K = V2/V1. The Miller theorem may be proved by using the equivalent two-port network technique to replace the two-port to its equivalent and by applying the source absorption theorem. Miller theorem implies that an impedance element is supplied by two arbitrary (not necessarily dependent) voltage sources that are connected in series through the common ground. In practice, one of them acts as a main (independent) voltage source with voltage V1 and the other - as an additional (linearly dependent) voltage source with voltage V2 = KV1 . The idea of Miller theorem (modifying circuit impedances seen from the sides of the input and output sources) is revealed below by comparing the two situations - without and with connecting an additional voltage source V2 . If V2 was zero (there was not a second voltage source or the right end of the element with impedance Z was just grounded), the input current flowing through the element would be determined, according to Ohm’s law, only by V1 Iin0 = VZ1 and the input impedance of the circuit would be 1 =Z Zin0 = IVin0 As a second voltage source is included, the input current depends on both the voltages. According to its polarity, V2 is subtracted from or added to V1 ; so, the input current decreases/increases 2 Iin = V1 ≠V = (1≠K) V1 = (1 ≠ K)Iin0 Z Z and the input impedance of the circuit seen from the side of the input source accordingly increases / decreases Z Zin = IVin1 = 1≠K So, Miller theorem expresses the fact that connecting a second voltage source with proportional voltage V2 = KV1 in series with the input voltage source changes the effective voltage, the current and respectively, the circuit impedance seen from the side of the input source. Depending on the polarity, V2 acts as a



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supplemental voltage source helping or opposing the main voltage source to pass the current through the impedance.

7

Tellegen’s theorem

The Tellegen theorem is applicable to a multitude of network systems. The basic assumptions for the systems are the conservation of flow of extensive quantities (Kirchhoff’s current law, KCL) and the uniqueness of the potentials at the network nodes (Kirchhoff’s voltage law, KVL). The Tellegen theorem provides a useful tool to analyze complex network systems including electrical circuits, biological and metabolic networks, pipeline transport networks, and chemical process networks. Consider an arbitrary lumped network whose graph G has b branches and nt nodes. In an electrical network, the branches are two-terminal components and the nodes are points of interconnection. Suppose that to each branch of the graph we assign arbitrarily a branch potential difference Wk and a branch current Fk f or k = 1, 2, . . . , b, and suppose that they are measured with respect to arbitrarily picked associated reference directions. If the branch potential differences W1 , W2 , . . . , Wb satisfy all the constraints imposed by KVL and if the branch currents F1 , F2 , . . . , Fb satisfy all the constraints imposed by KCL, then b ÿ

W k Fk = 0

k=1

Tellegen’s theorem is extremely general; it is valid for any lumped network that contains any elements, linear or nonlinear, passive or active, time-varying or time-invariant. The generality is extended when Wk and Fk are linear operations on the set of potential differences and on the set of branch currents (respectively) since linear operations don’t affect KVL and KCL. Incidence matrix: The nt ◊nf matrix Aa is called node-to-branch incidence matrix for the matrix elements aij being Y _1, if flow j leaves node i ] aij = ≠1, if flow j enters node i _ [ 0, if flow j is not incident with node i A reference or datum node P0 is introduced to represent the environment and connected to all dynamic nodes and terminals. The (nt ≠1)◊nf matrixA, where the row that contains the elements a0j of the reference node P0 is eliminated, is called reduced incidence matrix. The conservation laws (KCL) in vector-matrix form:

shop.ssb cra ck.com AF = 0

The uniqueness condition for the potentials (KVL) in vector-matrix form: W = AT w where wk are the absolute potentials at the nodes to the reference node P0 . Using KVL: WT F = (AT w)T F = (wT A)F = wT AF = 0

(1)

because AF = 0 by KCL. So: b ÿ

W k Fk = W T F = 0

k=1

8

Maximum power transfer theorems

A very useful power theorem may be developed with reference to a practical voltage or current source. For the practical voltage source, the power delivered to the load RL is



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PL = i2L RL =

vs2 RL (Rs + RL )2

To find the value of R L that absorbs maximum power from the given practical source, we differentiate with respect to RL : dPL (Rs + RL )2 vs2 ≠ vs2 RL (2)(Rs + RL ) = dRL (Rs + RL )2 and equate the derivative to zero, obtaining 2RL (Rs + RL ) = (Rs + RL )2 or Rs = R L

Definition An independent voltage source in series with a resistance Rs , or an independent current source in parallel with a resistance Rs , delivers maximum power to a load resistance RL such that RL = Rs . maximum power transfer requirement that RL = Rs = RT H will provide Pmax |deliveredtoload =

8.1

vs2 v2 = TH 4Rs 4RT H

Example:

Choose a load resistance so that maximum power is transferred to it from the amplifier, and calculate the actual power absorbed.

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Solution: Since it is the load resistance we are asked to determine, the maximum power theorem applies. The first step is to find the Thevenin equivalent of the rest of the circuit. We first determine the Thevenin equivalent resistance, which requires that we remove RL and short-circuit the independent source as in figure below

Since vfi = 0, the dependent current source is an open circuit, and RT H = 1k . This can be verified by connecting an independent 1 A current source across the 1 k resistor; vfi will still be zero, so the dependent source remains inactive and hence contributes nothing to RT H . In order to obtain maximum power delivered into the load, RL should be set to RT H = 1k . To find vT H we consider the circuit shown in figure, which is figure with RL removed. vo c = ≠0.03vfi (1000) = ≠30vfi

where the voltage vfi may be found from simple voltage division:



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3864 ) 300 + 3864 so that our Thevenin equivalent is a voltage ≠69.6sin440tmV in series with 1 k The maximum power is given by vfi = (2.5 ◊ 10≠3 sin440t)(

Pm ax =

9

.

vT2 H = 1.211sin2 440tµW 4RT H

Response of First-order circuit

Impulse response of RL circuit

The impulse response for each voltage is the inverse Laplace transform of the corresponding transfer function. It represents the response of the circuit to an input voltage consisting of an impulse or Dirac delta function. The impulse response for the inductor voltage is

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R ≠t R 1 1 e L u(t) = ”(t) ≠ e≠ · t u(t) L · where u(t) is the Heaviside step function and hL (t) = ”(t) ≠

·=

L R

is the time constant. Similarly, the impulse response for the resistor voltage is hR (t) =

R ≠t R 1 1 e L u(t) = e≠ · t u(t) L ·

Step response of an RL Circuit

After the above switch is closed Kirchoff’s voltage law can be applied which gives: di dt Then rearranging the above we obtain the following equation: Vs = Ri + L



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di R = ≠ dt Vs L i≠(R)

We now integrate each side and using x and y as variables for the integration we get: ⁄

i(t)

0

thus integrating we get

ln

dx R =≠ L x ≠ ( VRs ) i(t) ≠ ( VRs ) I0 ≠

( VRs )

=≠

⁄

t

0

dt

R t L

where I0 is the current at time t=0 and i(t) is the current at any time after 0. Taking inverse logs and rearranging gives us the following equation: Vs Vs + (I0 ≠ )e≠(R/L)t R R When the initial energy in the inductor is 0, I0 is zero hence the above becomes: i(t) =

i(t) =

Vs Vs ≠ e≠(R/L)t R R

Ramp response of an RL Circuit With an applied ramp voltage, the RL circuit equation is di + Ri = bt + c dt The solution (current) for the LR circuit with an applied ramp voltage is always of the form: L

shop.ssb cra ck.com i(t) = Ae≠kt + Bt = C

It contains two parts: 1. The Complementary Function (CF), Ae≠kt , is the transient. -kt depends on the circuit parameters L and R only, so dictating that the time for transient decay is dependent only on the circuit itself. 2. The Particular Integral (PI), Bt + C, a ramp output, is the steady state. Note again, the type of steady state solution (long-term output) depends directly upon the type of applied voltage (input). Note: • If b and c are both zero (zero applied voltage), the steady state is zero. (Zero input implies zero steady state output) • If b = 0 and c is not zero, the steady state solution is constant. (Constant input implies constant steady state output) • If b is not zero, the steady state solution is a ramp. (Ramp input implies ramp steady state output)



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Sinusoidal response of an RL Circuit Consider the series RL circuit shown below

The sinusoidal source voltage vs = Vm cosÊt has been switched into the circuit at some remote time in the past, and the natural response has died out completely. di + Ri = Vm cosÊt dt obtained by applying KVL around the simple loop. At any instant where the derivative is equal to zero, we see that the current must have the form i Ã cosÊt. Similarly, at an instant where the current is equal to zero, the derivative must be proportional to cosÊt, implying a current of the form sinÊt . We might expect, therefore, that the forced response will have the general form: L

shop.ssb cra ck.com i(t) = I1 cosÊt + I2 sinÊt

where I1 and I2 are real constants whose values depend upon Vm , R, L, and Ê. No constant or exponential function can be present. Substituting the assumed form for the solution in the differential equation yields L(≠I1 ÊsinÊt + I2 ÊcosÊt ) + R(≠I1 ÊsinÊt + I2 ÊcosÊt ) If we collect the cosine and sine terms, we obtain (≠LI1 Ê + RI2 )sinÊt + (LI2 Ê + RI1 ≠ Vm )cosÊt = 0

This equation must be true for all values of t, which can be achieved only if the factors multiplying cos Êt and sin Êt are each zero. Thus,

Therefore,

≠ÊLI1 + RI2 = 0

and

RVm R2 + Ê 2 L2 Thus, the forced response is obtained: I1 =

i(t) =


ÊLI2 + RI1 ≠ Vm = 0 I2 =

ÊLVm R2 + Ê 2 L2

RVm ÊLVm cosÊt + 2 sinÊt R2 + Ê 2 L2 R + Ê 2 L2


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10

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Response of Second-order circuit

Impulse response of an RLC Circuit

The equation that describes the response of the system is obtained by applying KVL around the mesh vR + vL + vc = V s The current flowing in the circuit is i=C And thus the voltages vR and vL are given by

dvc dt

vR = iR = RC vL = L Therefore,

dvc dt

di d2 vc = LC 2 dt dt

d2 vc R dvc 1 1 + + vc = vs 2 dt L dt LC LC The solution to equation is, vc = vcp + vch The particular solution is

shop.ssb cra ck.com vcp = Vs

Assuming a homogeneous solution is of the form Aest and by substituting we get s2 + By defining we get –=

R 1 s+ =0 L LC

R , 2L

Ê0 = Ô

1 LC

Step Response of an RLC Circuit

Transfer function: Vc (s) 1 = Vs (s) LCs2 + RCs + 1 The resonant frequency here is defined as the frequency at which the amplitude of the impedance or the admittance of the circuit has a minimum. f=


1 Ô 2fi LC


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Sinusoidal Response of an RLC Circuit

Differential equation governing the system is: d2 v(t) R dv(t) 1 1 + + v(t) = vs (t) dt2 L dt LC LC Assuming that the input is a complex exponential whose real part is the given vs (t) provides: vs (t) = 2ejÊt The output is assumed to have the phasor form: v(t) = V¯ ejÊt where V¯ contains the (unknown) magnitude and phase of the output voltage. ≠(jÊ)2 V¯ ejÊt +

R 1 1 (jÊ)V¯ ejÊt + (jÊ)V¯ ejÊt = 2ejÊt L LC LC

dividing through by ejÊt and noting that j 2 = ≠1, results in

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so that

1 R 2 ≠ Ê 2 + j Ê]V¯ = LC L LC V¯ =

The magnitude and phase of V¯ are | V |= Ò ”

11

1 LC

2/LC ≠ Ê2 + j R LÊ 2/LC

1 2 ( LC ≠ Ê 2 )2 + ( R L Ê)

V = ≠tan≠1 (

RÊ/L ) ≠ Ê2

1 LC

Two port parameters

Admittance parameters Consider the two-port as it is shown in figure below



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the voltage and current at the input terminals are V1 and I1 , and V2 and I2 are specified at the output port. The directions of I1 and I2 are both customarily selected as into the network at the upper conductors. Since the network is linear and contains no independent sources within it, I1 may be considered to be the superposition of two components, one caused by V1 and the other by V2 . When the same argument is applied to I2 , we may begin with the set of equations I1 = y11 V1 + y12 V 2 I2 = y21 V1 + y22 V 2 where the y’s are no more than proportionality constants, or unknown coefficients, for the present. However, it should be clear that their dimensions must be A/V, or S. They are therefore called the y (or admittance) parameters. Define column (2x1) matrix I, 5 6 I I= 1 I2 Define square (2x2) matrix y,

Define column (2x1) matrix V,

5 y y = 11 y21

y12 y22

6

5 6 V V = 1 V2

Thus, we may write the matrix equation, I = yV Therefore, 5 6 5 I1 y V = 11 1 I2 y21 V1

shop.ssb cra ck.com y12 V2 y22 V2

6

Each of the y parameters may be described as a current-voltage ratio with either V1 = 0 (the input terminals short-circuited) or V2 = 0 (the output terminals short-circuited): y11 =

I1 |V V1 2=0

y12 =

I1 |V V2 1=0

y21 =

I2 |V V1 2=0

y22 =

I2 |V V2 1=0

Because each parameter is an admittance which is obtained by short- circuiting either the output or the input port, the y parameters are known as the short-circuit admittance parameters. The specific name of y11 is the short-circuit input admittance, y22 is the short-circuit output admittance, and y12 and y21 are the short-circuit transfer admittances.



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Impedance parameters

let us consider the voltage V1 as the response produced by two current sources I1 and I2 . We thus write for V1 V1 = z11 I1 + z12 I2 similarly for V2 V2 = z21 I1 + z22 I2 Matrix V = ZI gives 5 6 5 6 5 6 V1 z z12 I1 = 11 V2 z21 z22 I2 The most informative description of the z parameters, is obtained by setting each of the currents equal to zero. Z11 =

V1 |I I1 2=0

Z12 =

V1 |I I2 1=0

Z21 =

V2 |I I1 2=0

shop.ssb cra ck.com V2 |I I2 1=0 Since zero current results from an open-circuit termination, the z parameters are known as the open-circuit impedance parameters. Z22 =

Hybrid parameters The hybrid parameters are defined by writing the pair of equations relating V1 , I1 , V2 and I2 as if V1 and I2 were the independent variables: V1 = h11 I1 + h12 V2 I2 = h21 I1 + h22 V2 5 6 5 6 V1 I =h 1 I2 V2 The nature of the parameters is made clear by first setting V2 = 0. Thus, h11 = VI11 |V2=0 , short-circuit input impedance h21 = II21 |V2=0 , short-circuit forward current gain Let I1 = 0 h12 = VV12 |I1=0 , open-circuit reverse voltage gain h22 = VI22 |I1=0 , open-circuit output admittance Since the parameters represent an impedance, an admittance, a voltage gain,and a current gain, they are called the ’hybrid’ parameters. Engineering Knowledge Test


Page: 17

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Application of Laplace transform

Laplace transform, defined for a general function f(t) as ⁄ Œ F (s) = e≠st f (t)dt ≠Œ

Laplace transforms of simple time functions: ⁄ Œ V (s) = e≠st v(t)dt = L[v(t)] 0≠

which, along with the expression for the inverse transform, 1 v(t) = 2fij Unit-Step Function u(t) L[u(t)] =

⁄

⁄

‡0 +jŒ

est V (s)ds = L≠1 [V (s)]

‡0 ≠jŒ

Œ

≠st

e

u(t)dt =

o≠

⁄

Œ

e≠st dt =

o

1 sx

Unit-Impulse Function ”(t ≠ t0 )

The unit-impulse function is defined to have an area of unity, so that ”(t ≠ t0 ) = 0, ⁄

t0 +Á

t ”= t0

”(t ≠ t0 )dt = 1

shop.ssb cra ck.com t0 ≠Á

where Á is a small constant. Thus, this ’function’ has a non-zero value only at the point t0 . For t0 > 0≠ , we therefore find the Laplace transform to be ⁄ Œ L[”(t ≠ t0 )] = e≠st ”(t ≠ t0 )dt = e≠st 0≠

Exponential Function L[e≠–t u(t)] =

⁄

L[tu(t)] =

⁄

Ramp Function

Œ

0≠

e≠–t e≠st =

Œ

0≠

te≠st dt =

1 s+–

1 s2

Properties of Laplace Transforms Constant multiple If a is a constant and f(t) is a function of t, then L[a.f (t)] = a.L[f (t)] Linearity property If a and b are constants while f(t) and g(t) are functions of t, then L[a.f (t) + b.g(t)] = a.L[f (t)] + b.L[g(t)] Change of Scale Property If L[f (t)] = F (s) then L[f (at)] =


1 s F( ) a a Network Theory Design

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Shifting property L[eat f (t)] = F (s ≠ a)

Time-Shift property L[f (t ≠ a)u(t ≠ a)] =

13

⁄

Œ

0≠

e≠st f (t ≠ a)u(t ≠ a)dt =

⁄

Œ

a≠

e≠st f (t ≠ a)dt = e≠as F (s)

Inverse Laplace transform

Given that, if F(s) = L[f(t)] and f(t) is continuous and of exponential order: f (t) = L≠1 [F (s)] Convolution L≠1 [F (s)G(s)] =

⁄

0

t

f (u)g(t ≠ u)du

Laplace Transform Pairs

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Laplace Transform Operations

14

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Application of Fourier series

• The Fourier theorem states that provided a function f (t) satisfies certain key properties, it may be represented by the infinite series a0 +

Œ n=1 (an cosnÊo t

+ bn sinnÊo t)

where, 1 a0 = ( ) T 2 an = ( ) T 2 bn = ( ) T

⁄

T

0

⁄

0

T

⁄

0

T

f (t)dt

f (t)cosnÊ0 t dt f (t)sinnÊ0 t dt

• A function f (t) possesses even symmetry if f (t) = f (-t).

• A function f (t) possesses odd symmetry if f (t) = - f (-t).

• A function f (t) possesses half-wave symmetry if f (t) = - f (t - 12 T ).

• The Fourier series of an even function is composed of only a constant and cosine functions. • The Fourier series of an odd function is composed of only sine functions.

• The Fourier series of any function possessing half-wave symmetry contains only odd harmonics.

• The Fourier series of a function may also be expressed in complex or exponential form, where f (t) = s T /2 n=Œ jnÊo t where, Cn = T1 ≠T /2 e≠jnÊo t F (t)dt n=≠Œ Cn e Engineering Knowledge Test



'

Network(Theory(Design(MCQs(

Network'Theory'Design'MCQs'

! 1.''One'coulomb'charge'is'equal'to'the'charge'on' (a)' ! 6.24&×10*+ &,-,./0123& (b)' 4 6.24×&1056 &,-,./0123& (c)' . 6.24×10*+ &!/173& (d)' (9)&212,&1;&/ℎ,&!41=,& ' 2.''The'correct'relation'between'energy'and'charge'is' (a)' Energy'='voltage'/'charge' (b)' Charge'='Energy'x'voltage' L.M (c)' Energy& = &voltage& charge ' (d)' Energy'='voltage'x'charge' ' 3.''In'a'practical'voltage'source,'the'terminal'voltage' (a)' cannot'be'less'than'source' (b)' cannot'be'higher'than'source' voltage' voltage' (c)' is'always'less'than'source' (d)' is'always'equal'to'source'voltage' voltage' ' 4.''An'ideal'current'source'has' (a)' infinite'source'resistance' (b)' zero'source'resistance' (c)' large'value'of'source'resistance' (d)' finite'value'of'source'resistance' ' 05.'Kirchhoff’s'laws'are'applicable'to' (a)' dc'only' (b)' as'sinusoidal'wave'only' (c)' dc'and'ac'sinusoidal'waves' (d)' all'wave'shapes' ' 06.'When'determining'The'venin’s'resistance'of'a'circuit' (a)' all'sources'must'be'open' (b)' all'sources'must'be'short'circuited' circuited' (c)' all' voltage' sources' must' be' (d)' all'sources'must'be'replaced'by' open' circuited' and' all' current' their'internal'resistances' sources'must'be'short'circuited' ' 07.'A'source'is'delivering'maximum'power'to'a'resistance'through'a'network.'The' ratio'of' power'delivered'to'the'source'power' (a)' is'always'0.5' (b)' may'be'0.5'or'less' (c)' may'be'0.5'or'less'or'more' (d)' may'be'0.5'or'more' '

'


'


08.'Three'resistance'of'15Ω'each'are'connected'in'delta.'The'resistance'of' equivalent'star'will' have'a'value'of' (a)' 12Ω' (b)' 5Ω' (c)' '5/3Ω' (d)' 45Ω' ' 09.'In'a'purely'inductive'circuit'the'current'…….the'voltage'by'…..' (a)' lags,'0°''' (b)' leads,'90°''' (c)' 'lags,'90°' (d)' lags,'45°' ' 10.'In'a'purely'capacitive'circuit,'the'current..…..the'voltage'by…….' (a)' lags,'0°' (b)' leads,'90°' (c)' lags,'90°' (d)' lags,'45°' ' ' 11.'A'bulb'rated'at'60W,'120V'is'used'for'30'minutes.'The'charge'associated'with' this' operation'is' (a)' 3600'C' (b)' 900'C' (c)' 7200'C' (d)' 60C' ' 12.'For'an'ideal'transformer,' (a)' both'z'and'y'parameters'exist.' (b)' neither'z'nor'y'parameters'exist.' (c)' z]parameters'exist,'but'not'the' (d)' y]parameters'exist,'but'not'the'z] y]parameters.' parameters.' ' 13.''Superposition'theorem'is'applicable'only'to'networks'that'are:' (a)' linear' (b)' nonlinear' (c)' time]invariant' (d)' passive' ' '14.'The'rms'value'of'the'a]c'voltage'v(t)'='200sin'314't'is:' (a)' 200'V' (b)' 314'V' (c)' 157.23'V' (d)' 141.42'V' ' 15.''Maximum'power'is'delivered'from'a'source'of'complex'impedance'NO 'to'a' connected'load'of'Scomplex'impedance'NP 'when' (a)' (A)'NP & = & NQ ' (b)' (B)'│NP │& = │NQ │' '


(c)' (C)'∠&NP & = &∠NO '

'


(d)' (D)'NP = NO∗ '

' 16.'Resistivity'of'a'wire'depends'on' (a)' length' (b)' material' (c)' cross'section'area' (d)' none'of'the'above' ' 17.'Resistance'of'a'wire'is'r'ohms.'The'wire'is'stretched'to'double'its'length,'then' its'resistance'in'ohms'is' (a)' r'/'2' (b)' 4'r' (c)' 2'r' (d)' r'/'4' ' 18.'Kirchhoff's'second'law'is'based'on'law'of'conservation'of' (a)' charge' (b)' energy' (c)' momentum' (d)' mass' ' 19.'Two'bulbs'marked'200'watt]250'volts'and'100'watt]250'volts'are'joined'in' series'to'250'volts'supply.'Power'consumed'in'circuit'is' (a)' 33'watt' (b)' 67'watt' (c)' 100'watt' (d)' 300'watt' ' 20.'Ohm's'law'is'not'applicable'to' (a)' DC'circuits' (b)' high'currents' (c)' small'resistors' (d)' semi]conductors' ' ' ' ' '21.'Kirchhoff’s'law'is'applicable'to'' (a)' AC'and'DC'circuits' (b)' AC'circuits'only' (c)' DC'circuits'only' (d)' Passive'networks'only' ' 22.'To'carry'a'current'of'0.3'amperes,'a'100'ohm'resistor'is'needed'in'an'electric' circuit.'A'resistor'you'would'select'is' (a)' 100'ohm,'7.5'watts' (b)' 100'ohm,'10'watts' (c)' 100'ohm,'1'watt' (d)' 100'ohm,'5'watts' ' 23.'One'or'more'than'one'source'of'emf'is'present'in'

'


'

(a)' Non]linear'network' (c)' Active'network'


(b)' Electric'network' (d)' Passive'network'

' 24.'For'a'2'port'network,'the'condition'AD]BC'='1'implies'that'the'network'is'' (a)' Unilateral'element'network' (b)' Lumped'element'network' (c)' Lossless' (d)' Reciprocal' ' 25.'Let'the'inductance'of'the'circuit'is'16'H'and'a'current'of'6'ampere'flows' through'it.'The'energy'stored'will'be' (a)' 288'joules' (b)' 500'joules' (c)' 144'joules' (d)' 1563'joules' ' 'Answers:(Network(Theory(Design(MCQs( 1.!!(a)!

2.!(d)!

3.!(b)!

4.!(a)!

! 5.!(d)!

6.!(d)!

7.!(b)!

8.!(b)!

9.!(c)!

10.!(b)!

11.!(b)! 12.!(a)! 13.!(a)! 14.!(d)! 15.!(d)! 16.!(b)! 17.!(b)! 18.!(b)! 19.!(b)! 20.!(d)!

21.!(a)! 22.!(b)! 23.!(c)! 24.!(d)! 25.!(a)! !

! '

'

!

!

!

!

Switching Theory Contents 1 Traffic

2

2 Switching systems

2

3 Grade of Service and blocking probability

4

4 Circuit switching and packet switching

5

5 Network traffic load and parameters

6

6 Modelling of switching systems

7

7 Incoming traffic and service time characterisation

7

8 Blocking models and loss estimates

8

9 Delay systems

9

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1

Page: 2

1

Traffic

The traffic is defined as the occupancy of server, its basic purpose is to determine the conditions under which adequate service is provided to subscribers while making economical use of the resources.

Statistics The statistical description of a traffic is important for the analysis and design of any switching network. • Calling rate

This is the average number of requests for connection that are made per unit time. If the instant in time that a call request arises is a random variable, the calling rate may be stated as the probability that a call request will occur in a certain short interval of time. If ’n’ is the the average number of call to and from a terminal during a period T seconds, the calling rate is defined as ⁄=

n T

• Holding time

The average holding time or service time ’h’ is the average duration of occupancy of a traffic path by a call. For voice traffic, it is the average holding time per call in hours or 100 seconds and for data traffic, average transmission per message in seconds. The reciprocal of the average holding time referred to as service (µ) in calls per hour is given as µ=

1 h

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• Distribution of destinations

Number of calls receiving at a exchange may be destined to its own exchange or a foreign exchange. The destination distribution is described as the probability of a call request being for a destination. As the hierarchical structure of telecommunication network includes many intermediate exchanges, the knowledge of this parameter helps in determining the number of trunks needed between individual centres.

• Average occupancy

If the average number of calls to and from a terminal during a period T seconds is ’n’ and the average holding time is ’h’ seconds, the average occupancy of the terminal is given by A=

2

nh ⁄ = ⁄h = T µ

Switching systems

The communication switching system enables the universal connectivity. The universal connectivity is realized when any entity in one part of the world can communicate with any other entity in another of the world. In many ways telecommunications will act as a substitute for the increasingly expensive physical transportation. The telecommunication links and switching were mainly designed for voice communication, with the appropriate equipments they can be used to transmit data. Therefore it needs new facilities including very high bandwidth switch data networks and large communication satellites with small, cheap earth antennas.


Switching Theory

Page: 3 Basics of switching system • Inputs and outputs

A major component of a switching system is the set of inputs and outputs circuits called inlets and outlets.

• Switching matrix or network

Switching matrix or network is the hardware part used to establish a connection between a given inlets and outlets.

• Symmetric network

Symmetric network is the one where number of inlets is equal the number of outlets of a switching system.

shop.ssb cra ck.com • Folded network

When all the inlets and outlets are connected to the subscriber lines, the logical connection appears. In this case, the output lines are folded back to the input and hence the network is called a folded network.

• Non folded network

When all the outlets lines are not connected to the subscriber lines (inlets), then it is known as non folded network.


Switching Theory

Page: 4 Functions of a switching system • Attending:

The system must be continually monitoring all lines to detect call requests.

• Information receiving:

In addition to receiving call and clear signals the system must receive information from the caller as to the called line or other service required.

• Information processing:

The system must process the information received, in order to determine the actions to be performed and to control these actions. Since both originating and terminating calls are handled different for different customers.

• Busy testing: Having processed the received information to determine the required outgoing circuit the system must make a busy test to determine whether it is free or already engaged on another call. • Interconnection:

A connection to the calling terminal or subscriber, connection to the called or terminal or subscriber and a connection between two terminals. These are the ways a call is between two or more customers are connected.

• Alter:

Having made connection, the system sends a signal to alert the called customer to the call.

3

Grade of Service and blocking probability

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On the loss system, the traffic is carried by network generally lower from real traffic that offered to network by customers. This overload traffic cannot proceed by network and will be loss traffic. Total this loss traffic is an index from network service quality, is called Grade of Service (GOS), and definition as ratio between loss traffic and offered traffic to network. Offered traffic itself actually is result from total call average from customers and average per call occupation time. Mathematically can explained with equation: GOS = (A-Y)/A Because (A-Y) = R = lost traffic Grade of service = GOS = R/A Smaller grade of services value, better services that produced. Example, if recommended that grade of services is 0,002, this mean there is two call from every 1000 call or call from every 500 call that offered customer is missing (cannot proceed). If, in one network condition, total customers is same with total server then GOS is same with zero, because every customers that will build a connection will always got success to occupation the server. Network system itself is non-blocking network. Blocking probability definition as probability that all server on busy network system (dwelled). When all servers busy, then the system is no more to process incoming traffic. In this situation incoming traffic is believed to experience blocking. Comprehension of GOS with blocking probability truly almost same, that is to explain about call size that cannot serve by network system. Main different between both is, GOS is a size with point of view from network side or switching system. GOS measured based on observation total call from customers that cannot loaded, whereas blocking probability based on observation busy server (dwelled) on switching system. To distinguish between both clearly, GOS usually named as call congestion (call jam, because showing part from call that rejected or unloaded) or probability loss, whereas blocking probability as time congestion (time jam, because showing part from time which all server or busy line).

Classification of switching system Basically Switching systems are of two types one is Manual s/w System and second one is Automatic s/w System and can be further classified as discussed below


Switching Theory

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4

Circuit switching and packet switching

Circuit switching In circuit switching network dedicated channel has to be established before the call is made between users. The channel is reserved between the users till the connection is active. For half duplex communication, one channel is allocated and for full duplex communication, two channels are allocated. It is mainly used for voice communication requiring real time services without any much delay.

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if user-A wants to use the network it need to first ask for the request to obtain the one and then user-A can communicate with user-C. During the connection phase if user-B tries to call/communicate with user-D or any other user it will get busy signal from the network.

Packet switching In packet switching network unlike CS network, it is not required to establish the connection initially. The connection/channel is available to use by many users. But when capacity or number of users increases then it will lead to congestion in the network. Packet switched networks are mainly used for data and voice applications requiring non-real time scenarios.


Switching Theory

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If user-A wants to send data/information to user-C and if user-B wants to send data to user-D, it is simultaneously possible. Here information is padded with header which contains addresses of source and destination. This header is sniffed by intermediate switching nodes to determine their route and destination.

Circuit switching vs packet switching In Packet switched (PS)networks quality of service (QoS)is not guaranteed while in circuit switched (CS) networks quality is guaranteed. PS is used for time insensitive applications such as internet/email/SMS/MMS/VOIP etc. In CS even if user is not talking the channel cannot be used by any other users, this will waste the resource capacity at those intervals. The example of circuit switched network is PSTN and example of packet switched network is GPRS/EDGE

5

Network traffic load and parameters

The traffic load is determined from the number or volume of calls intensity ⁄ and service time (mean holding time) µ. Traffic can be characterized into the various traffic types as shown below:

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• Offered traffic A

• Carried traffic Ac (flow traffic) • Block traffic Ab (loss traffic)

Offered traffic = Carried traffic + block traffic A = Ac + Ab Offered traffic A = ⁄ ◊ µ Traffic load can be affected by various factors such are: • Area of a cell (reduce the size of cell) • Number of channels or truck per cell • Cluster size

• Spectrum efficiency

• Bandwidth per channel Parameters: • Call completion rate CCR: It is defined as the ratio of the number of the calls to the number of call attempts. • Busy hour call attempts: The number of call attempts in the busy hour is called busy hour call attempts BHCA. Average busy hour calls = BHCA x CCR


Switching Theory

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Modelling of switching systems

In switching systems, traffic related all problems must be solved through analysis. For this, a model, which gives mathematical behaviour of physical quantity under consideration is necessary. A suitable model is chosen for handling a particular switching system and circumstance. The behaviour of the switching system or network can be studied as random process. A random process or stochastic process can be defined as a process in which one or more quantities can not be determined properly but can be predicted under certain probability. The quantities are called random variables. In a similar fashion, telephone traffic can be described as random process where the number of subscribers who generate the call and the number of busy servers are random variables, with certain probabilities, a prediction can be made for calculation of the number of active subscribers in a specific time interval. The random variables regarding the telephone traffic are discrete in nature. On the other hand, random variables in case of temperature variation experiment can take on continuous variables. Sometime both types of variables are found in a particular process. Thus, there are four different types of random processes • Continuous time continuous state

The statistical properties obtained using continuous-time-continuous-state method are known as time statistical parameters.

• Continuous time discrete state

The statistical properties obtained using continuous-time-discrete-state method are refereed as ensemble statistical parameters.

• Discrete time Continuous state • Discrete time discrete state

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The random process with identical time and ensemble average called ergodic process. For modelling, it is difficult for non-stationary process like telephone traffic. But during busy hour traffic may be considered as stationary or ergostic process.

7

Incoming traffic and service time characterisation

Traffic in the telecommunication network is the summation of individual traffic generated by the subscribers and its characterized as a random process. When any subscriber generates a call it adds the number o arriving calls. Once the number arrived, there is no way to reduce the number. So it can be said that it is a special case of birth-death process in which death rate is zero. For this, we need a model that describes an originating process. Such a process is known as renewal process. In other words, this process is a pure birth process that increases the population or traffic. The equations governing the dynamics of a renewal process can be easily arrived at from the B-D process equations Pk≠1 ⁄k≠1 + Pk+1 µk+1 ≠ (⁄k + µk )Pk = 0 P1 µ1 ≠ ⁄o Po

f or K Ø 1

f or K = 0

dPk (t) = Pk≠1 (t)⁄k≠1 ≠ ⁄k Pk (t) f or k Ø 1 dt

For constant birth rate ⁄

dPk (t) = ≠⁄0 P0 (t)....f or k = 0 dt dPk (t) = Pk≠1 (t)⁄ ≠ ⁄Pk (t) f or k Ø 1 dt dPk (t) = ≠⁄P0 (t)....f or k = 0 dt


Switching Theory

Page: 8 Now, we assume certain boundary conditions i.e. at time t = 0, the system is in state zero or no birth have taken place. So, we have Pk (0) = 1 f or K = 0 Pk (0) = 0 f or K ”= 0

Therefore,

Po (t) = e≠⁄t Thus for k = 1 dp1 (t) = ≠⁄P1 (t) + ⁄e≠⁄t dt P1 (t) = ⁄te≠⁄t f or k = 2 P2 (t) =

(⁄t)2 e≠⁄t 2!

P2 (t) =

(⁄t)2 e≠⁄t k!

Thus, the general solution or equation is,

8

Blocking models and loss estimates

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If the incoming calls finds all available lines busy, the call is said to be blocked. The blocked calls can be handled in two ways-one is loss system and another one is delay system. In loss system, overflow traffic or blocked calls are simply refused or rejected or lost. The behaviour of loss system is studied by using blocking models. In delay system, a blocked call remains in the system and waits in a queue for a free line. The behaviour of delay system is studied by queuing models. In this section, we discuss about loss system. The overflow traffic created in the loss system may be handled by three different ways. They are • The rejected traffic by a particular resources may be hand. by another resources in Telecommunication switching network. • After sometime the rejected traffic may return to the same resources.

• The overflow traffic is actually serviced when the resources become available but it is virtually seen that the traffic is serviced by the resources. Here call is accepted and allowed to proceed with his information exchange process. Considering these three cases, there are three models of loss systems • Lost Calls Cleared (LCC)

• Lost Calls Returned (LCR) • Lost Calls Held (LCH)

Lost Calls Cleared (LCC) are divided in two parts • Lost Calls Cleared System with infinite sources.

• Lost Calls Cleared System with finite subscribers. • All the models are described in this section.


Switching Theory

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Delay systems

Markovian queuing model An M/M/c queue is a stochastic process whose state space is the set 0, 1, 2, 3, ... where the value corresponds to the number of customers in the system, including any currently in service. • Arrivals occur at rate ⁄ according to a Poisson process and move the process from state i to i+1. • Service times have an exponential distribution with parameter Î in the M/M/c queue.

• There are c servers, which serve from the front of the queue. If there are less than c jobs, some of the servers will be idle. If there are more than c jobs, the jobs queue in a buffer. • The buffer is of infinite size, so there is no limit on the number of customers it can contain.

Markov process, named after the Russian mathematician Andrey Markov, is a time-varying random phenomenon for which a specific property the Markov property holds. Markov Chain: If we assume that the state space, I, is discrete, then the Markov process is known as a Markov Chain DTMC(Discrete Time Markov Chain): If the parametric space , T, is also discrete, then the Markov chain is known as a discrete time Markov chain. In this case we let T= 0,1,2,.... For a DTMC the Markov property can be stated as P (Xn = In | Xo = Io , X1 = I1 ...Xn≠1 = In≠1 = P (Xn = In | Xn≠1 = In≠1 )

M/M/1/ Œ The M/M/1 queuing system is described as a queuing model where:

• arrivals are a Poisson process i.e. inter-arrival time is exponentially distributed • service time is exponentially distributed;

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• there is one server

• the length of queue in which arriving users wait before being served is infinite

• the population of users (i.e. the pool of users) available to join the system is infinite

Steady State Distribution Let pn represents the probability mass function of a discrete random variable denoting the number of customers in the system in long run pn = (1 ≠ fl)fln

fl<1

Transient solution The transient probabilities pn(t)=PrX(t)=n for an M/M/1 queue are given by pn (t) = e≠ ⁄µt[

  ⁄(n≠1)/2 ⁄(n≠t≠1)/2 ⁄ ⁄n In≠t (2 ⁄µt) + In+t+1 (2 ⁄µt) + (1 ≠ ) µ µ µ µ

for all n Ø 0

In (y) =


Œ k=0

⁄ Œ j=n+t+2 (

µ

≠j/2

 Ij (2 ⁄µt)]

(y/2)n+2k k | (n + k) | Switching Theory

Page: 10 Finite capacity In an M/M/c/K queue only K customers can queue at any one time. Any further arrivals to the queue are considered ”lost”. We assume that K Ø c. The model has transition rate matrix

on the state space 0, 1, 2, ..., c, ..., K. In the case where c = K, the M/M/c/c queue is also known as the Erlang-B model.

Queue discipline The queue discipline describes the method used to determine the order in which customers are served. The most common queue discipline is the FCFS discipline (first come, first served), in which customers are served in the order of their arrival. Under the LCFS discipline (last come, first served), the most recent arrivals are the first to enter service. If the next customer to enter service is randomly chosen from those customers waiting for service it is referred to as the SIRO discipline (service in random order). Finally we consider priority queuing disciplines. A priority discipline classifies each arrival into one of several categories. Each category is then given a priority level, and within each priority level, customers enter service on a FCFS basis. Another factor that has an important effect on the behavior of a queuing system is the method that customers use to determine which line to join.

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Multiple server A larger number of operational waiting line systems include multiple servers. These models can be very complex, so in this section we present only the most basic multiple-server (or channel) waiting line structure. This system includes a single waiting line and a service facility with several independent servers in parallel. An example of a multiple-server system is an airline ticket and check-in counter, where passengers line up in a roped-off single line waiting for one of several agents for service. The same waiting line structure is frequently found at the post office, where customers in a single line wait for service from several postal clerks. The formulas for determining the operating characteristics for the multiple-server model are based on the same assumptions as the single-server model–Poisson arrival rate, exponential service times, infinite calling population and queue length, and FIFO queue discipline. Also, recall that in the single-server model, m > l; however, in the multiple-server model, sm > l, where s is the number of servers. The operating characteristics formulas are as follows. The probability that there are no customers in the system (all servers are idle) is

The probability of n customers in the queuing system is


Switching Theory

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The probability that a customer arriving in the system must wait for service (i.e., the probability that all the servers are busy) is

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Switching Theory


'

Switching'Theory'MCQs'

Switching)Theory)MCQs) 1.'''Internet'uses' (a)' Packet'switching' (b)' Circuit'switching' (c)' Telephone'switching' (d)' Telex'switching' ' 2.''The'example'of'electromechanical'switching'system''' (a)' Crossbar'switching'system'' (b)' Reed'relay'switching'system'' (c)' Magneto'switching'system'' (d)' None'of'the'above' ' 3.''Which'type'of'switching'is'inefficient'of'transferring'long'messages?'' (a)' Circuit'switching'' (b)' Message'switching'' (c)' Packet'switching'' (d)' None'of'the'above' ' 4.''The'another'name'of'message'switching'is'' (a)' Line'switching'' (b)' Store'and'forward'switching'' (c)' Revers'switching' (d)' None'of'the'above' ' 5.''In'case'of'speed'of'dialing,'which'type'of'switch'is'advantageous''' (a)' Crossbar'switch'' (b)' Stronger'switch'' (c)' Reed'relay'switch'' (d)' None'of'the'above' ' 6.''The'expression'for'blocking'probability'of'STT'switch'is' ( % ( (a)' (b)' % ' ! = 1− ' ! = 1− 1− ' & & (c)'

%* ! =) 1 − 1 − +

(d)' ! = 1 − , ' ( '

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Information Technology

Contents 1 Operating system

2

2 RDBMS

7

3 Software engineering

20

4 Programming in C

27

5 Object-oriented programming

33

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1

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Operating system

Process A process is more than just a copy of a program in memory. An executable program is like a recipe. It’s a series of instructions which the computer reads in order to accomplish a task. When a cook prepares a dish, he reads the recipe, gathers all the materials the recipe calls for, and combines them as the recipe dictates. This is similar to the way that a program is run. When you run a program on your computer the operating system gathers resources (like memory and CPU time) and begins following the instructions listed in the executable. The OS must keep track of which instruction it’s performing at any given moment, and the current state of the program. All of this information, including the program itself, the list of resources allocated to it, and its state information, are part of a process. In multi-tasking operating systems, like Windows (95 and later), Linux, and MacOS, multiple processes can be run by the operating system at the same time, with each process taking turns running on the CPU. The operating system allocates time for each process to run on the CPU, and switches between each so quickly that they appear to run simultaneously. MS-DOS, which preceded Microsoft Windows, only ran one process one at a time. Processes are used to carry out every task that needs to be performed by the computer. The operating system itself is a process. It spawns (or starts) processes that run the display, interact with the keyboard, run the mouse, and interact with disk drives. There are processes that are started by the user such as word processors, spreadsheets, web browsers, and e-mail clients. Some of these programs consist of multiple co-operating processes; for example, a web server might have multiple processes to handle multiple incoming requests at the same time.

Interprocess Communication

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When designing an Operating System is Inter-Process Communication, or IPC. Essentially, when more than one process is running and sharing the same computer, there might be times when the processes need to communicate with another process or multiple processes might want to share the same resource. When this happens, care should be taken not to create certain dangerous conditions, namely, race conditions, where two processes attempt to use the same resource at the same time. Which ever is fastest gets first crack at it, but the other process then gets next crack and so on, confusing the resource. A deadlock occurs when two devices both lock into a waiting mode, waiting for the other to complete before they start, and so neither can complete, and other rarer and less predictable errors that are even harder to debug can occur as well.

Threads Although threads are sometimes not considered real processes because they do not carry all the heavy freight of a full process, concurrency using threads is just as fraught with problems as Inter-Process Communication. The primary difference is that a thread does not attach all the resources that a full process must. The specific difference lies in the context fields of the process. Instead of having their own context, threads inherit the context of the main process, they were spawned from, and so care must be taken that they do not change variables used by other threads without some communication synchronization happening. Threads are sometimes called lightweight processes. Both processes and threads provide an execution environment, but creating a new thread often requires fewer resources than creating a new process. Threads exist within a process - every process has at least one. Threads share the process’s resources, including memory and open files. This makes for efficient, but potentially problematic, communication.



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Concurrency Concurrency encompasses a host of design issues, including communication among processes, sharing and competing for resources (such as memory, files, and I/O access), synchronization of the activities of multiple processes, and allocation of processor time to processes. If more than one thread exists in system at once, these threads can execute independently or in cooperation. Problems with concurrent execution can be expressed as follows: • Concurrent processes (or threads) often need access to shared data and shared resources.

• If there is no controlled access to shared data, it is possible to end up with an inconsistent view of this data. • Maintaining data consistency requires mechanisms to ensure the orderly execution of cooperating processes. • Race conditions may arise due to different order of the relative execution of various programs

Deadlock Deadlock refers to a specific condition when two or more processes are each waiting for another to release a resource, or more than two processes are waiting for resources in a circular chain. Deadlock is a common problem in multiprocessing where many processes share a specific type of mutually exclusive resource known as a software, or soft, lock. Computers intended for the time-sharing and/or real-time markets are often equipped with a hardware lock (or hard lock) which guarantees exclusive access to processes, forcing serialization. Deadlocks are particularly troubling because there is no general solution to avoid (soft) deadlocks. There are four necessary conditions for a deadlock to occur, known as the Coffman conditions:

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• Mutual exclusion condition: a resource that cannot be used by more than one process at a time. • Hold and wait condition: processes already holding resources may request new resources. • No pre-emption condition: only a process holding a resource may release it.

• Circular wait condition: two or more processes form a circular chain where each process waits for a resource that the next process in the chain holds. Livelock Livelock is similar to a deadlock, except that the states of the processes involved in the livelock constantly change with regard to one another, none progressing. Livelock is a special case of resource starvation; the general definition only states that a specific process is not progressing.

CPU scheduling Because only one process per CPU can run at any one time, multitasking operating systems use a concept called multiprogramming to schedule time for each process to run on a CPU. A scheduler is responsible for giving each process time on the CPU. When the current time slice expires, the scheduler puts the current process to sleep and the next process is given CPU time. Some scheduling systems include: • First Come First Served: The first come, first served (commonly called FIFO â ä first in, first out) process scheduling algorithm is the simplest process scheduling algorithm. It is rarely used in modern operating systems, but is sometimes used inside of other scheduling systems. Information Technology


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• Shortest Process Next:Shortest Process Next (SPN) scheduling, also called Shortest Job First (SJF) scheduling, assigns the process estimated to complete fastest to the CPU as soon as CPU time is available. • Shortest Remaining Time: The Shortest Remaining Time (SRT) scheduling system is a more intelligent version of SPN that allows shorter processes to skip ahead as they appear, instead of only processing the shortest process at the time that CPU time becomes available. • Round Robin Scheduling: Round Robin scheduling is an older method of CPU time sharing. Each process is given a certain amount of CPU time (a time slice), and if it is not finished by the end of the time slice, the process is moved to the back of the process queue, and the next process in line is moved to the CPU. A common variant on Round Robin allows a process to give up the remainder of its time slice if it doesn’t need it. This might be because it is waiting for a particular event, or because it is completed. • Priority Scheduling: In Priority Scheduling, each process is given a priority, and higher priority methods are executed first, while equal priorities are executed First Come First Served or Round Robin.

Memory management Memory Management is a term used to describe how the operating system handles the available RAM. It is managed at multiple levels.

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Physical memory

At the most basic level, there is the physical memory. The physical memory’s size is the sum of the capacities of all RAM-modules (such as DDR SDRAM) installed in the system. For example, when you have two 512 MiB DDR SDRAM modules installed in your system, the OS will have 1 GiB of physical memory at its disposal. Segmented memory On top of the physical memory is the segmented memory. It uses the Memory Management Unit (MMU) to translate a logical address (specifying a segment and an offset) into a physical address (or linear address). This allowed early computers to address more than 64 KiB of memory. Most operating systems today don’t use a segmented memory model, preferring to use paging. Paged memory A paged memory model uses the MMU to translate virtual addresses to physical addresses. With paging, one can map multiple 4 KiB-sized chunks (called pages) to any virtual address. For example, data at offset 0◊1000 in physical memory might be mapped to address 0◊C0000000 (at offset 3 GiB) in virtual memory, even though the system may have only 32 MiB of physical RAM available. Accessing the data at address 0 ◊ C0000000 internally accesses the data at physical address 0 ◊ 1000. This provides processes with their own virtual address space which contains only the code and data required by that single process, and everything else is hidden. This way, a process can’t corrupt another process’ code or data, improving security and reliability. Allocated memory With paging, memory is managed in 4 KiB-sized chunks. Most applications require the ability to be able to get only a fraction of that size, to store data. The memory allocator gets a big chunk of memory and divides this into much smaller chunks. which it gives to the applications when requested. Information Technology


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Virtual memory Virtual memory is a memory management technique that offers two main benefits: 1. Each process ”thinks” it has all the system’s memory to itself. 2. It becomes possible to access more memory than the actual physical amount. Virtual memory is very useful and is implemented in most operating systems by using the memory management unit (MMU) in the CPU. The second is accomplished by the MMU setting up a small, contiguous portion of the hard drive and treating it like physical RAM. That is, the operating system will place memory segments or pages into the file as if it were loading it into actual RAM. Thus, it has a place to hold ”unused” pages of memory until they are needed and have a place to ”Swap Out” memory segments that are no longer needed in memory.

File systems A file system is a way of organizing information on a physical drive or other media (e.g, RAM) for access. In general, file systems can be divided into several groups: • Local file systems - ext2/3, FAT32, NTFS • Distributed file systems - NFS, AFS

• Parallel or cluster file systems - GFS, PVFS, Lustre A file system may be described by a set of characteristics:

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• Ability to work with huge number of files/directories in a directory (e.g ReiserFS).

• Large files support - some file systems have 2-4G limit for this. Switching to 64-bits addressing solves the problem. • Fragmentation - NTFS quickly becomes fragmented, while ext4 doesn’t.

• Fault tolerance - compare e2fsck runs on dirty ext2 vs logging facilities of ext3 or ReiserFS. • Scalability - some file systems have limits on their disk sizes. • Use of encryption/compression

• Charsets support - for example, FAT does not allow use of some symbols in file names, while NTFS does. • Long file names - for ext4, 256 chars; FAT16 8+3 chars max Abstraction One of the main points and features of a filesystem is abstraction. With a filesystem, we can organize our data into files, directories, and other constructs, and manipulate them in various ways. To open a file, you need only its path; it’s not necessary to figure out the exact location on disk and instruct the hard drive controller to move the read head to that position. This data abstraction is important for reasons like portability, security and convenience. Allocation The main idea behind allocation is effective utilization of file space and fast access of the files. There are three types of allocation - Contiguous allocation, Linked allocation and Indexed allocation.



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I/O systems I/O Subsystem is responsible to provide many services related to I/O - scheduling, buffering, caching, error handling, spooling and device reservation. I/O Hardware Daisy chain: When device A has a cable that plugs into device B, and device B has a cable that plugs into device C, and device C plugs into a port on the computer, this arrangement is called a daisy chain. It usually operates as a bus. Controller: A controller is a collection of electronics that can operate a port, a bus, or a device. A serial-port controller is an example of a simple device controller. This is a single chip in the computer that controls the signals on the wires of a serial port. I/O port: An I/O port typically consists of four registers, called the status , control, data-in, and data-out registers. Polling: Polling is a process by which a host waits for controller response.It is a looping process, reading the status register over and over until the busy bit of status register becomes clear. The controller uses/sets the busy bit when it is busy working on a command, and clears the busy bit when it is ready to accept the next command. The host signals its wish via the command-ready bit in the command register. The host sets the command-ready bit when a command is available for the controller to execute. Direct Memory Access (DMA) : Many computers avoid burdening the main CPU with programmed I/O by offloading some of this work to a special purpose processor. This type of processor is called, a Direct Memory Access(DMA) controller. A special control unit is used to transfer block of data directly between an external device and the main memory, without intervention by the processor. This approach is called Direct Memory Access(DMA). Interrupts: Interrupts allow devices to notify the CPU when they have data to transfer or when an operation is complete, allowing the CPU to perform other duties when no I/O transfers need its immediate attention.

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Protection and security

A great percentage of the operating systems that are used today have user account privileges. These privileges may be for security reasons, to make sure that someone does not leak internal company information out, or to protect the well-being of the computer from some people’s incompetence with a computer, or to prevent grave mistake from crashing the system, or to stop system failure or hacking of a computer (internally or externally) through an account with restricted access to files. Security is one of the most sought-after features in an operating system today. With computers now being used to store vast amounts of data, from top-secret government information to enterprises and business keeping track of bank account numbers, security in an operating system is a must. Within the next pages we will discuss the basics of OS security, from user authentication and cryptography to modern internet cryptographic algorithms. Segmentation is one of the most common ways to achieve memory protection. In a computer system using segmentation, an instruction operand that refers to a memory location includes a value that identifies a segment and an offset within that segment. A segment has a set of permissions, and a length, associated with it. If the currently running process is allowed by the permissions to make the type of reference to memory that it is attempting to make, and the offset within the segment is within the range specified by the length of the segment, the reference is permitted; otherwise, a hardware exception is raised. Swapping is basically implemented by Medium term scheduler.Medium term scheduler removes process from CPU for duration and reduce the degree of multiprogramming. And after some time these process can again be reintroduced into main memory. Process execution will again be resumed from the point it left CPU. This scheme is called swapping. More generally we can say swapping is removing of process from memory to secondary memory and again back to main memory.



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RDBMS

A database management system (DBMS) is a collection of programs that enables you to store, modify, and extract information from a database. There are many different types of DBMSs, ranging from small systems that run on personal computers to huge systems that run on mainframes. RDMS Relational Database Management System and pronounced as separate letters, a type of database management system (DBMS) that stores data in the form of related tables. Relational databases are powerful because they require few assumptions about how data is related or how it will be extracted from the database. As a result, the same database can be viewed in many different ways. An important feature of relational systems is that a single database can be spread across several tables. This differs from flat-file databases, in which each database is self-contained in a single table.

ER-model ER, Entity relationship model defines the conceptual view of database. It works around real world entity and association among them. At view level, ER model is considered well for designing databases. Entity A real-world thing either animate or inanimate that can be easily identifiable and distinguishable. For example, in a school database, student, teachers, class and course offered can be considered as entities. All entities have some attributes or properties that give them their identity. An entity set is a collection of similar types of entities. Entity set may contain entities with attribute sharing similar values. For example, Students set may contain all the student of a school; likewise Teachers set may contain all the teachers of school from all faculties. Entities sets need not to be disjoint.

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Attributes Entities are represented by means of their properties, called attributes. All attributes have values. For example, a student entity may have name, class, age as attributes. There exist a domain or range of values that can be assigned to attributes. For example, a student’s name cannot be a numeric value. It has to be alphabetic. A student’s age cannot be negative. Types of Attributes: • Simple attributes are atomic values, which cannot be divided further. For example, student’s phone-number is an atomic value of 10 digits. • Composite attributes are made of more than one simple attribute. For example, a student’s complete name may have first-name and last-name. • Derived attributes are attributes, which do not exist physical in the database, but there values are derived from other attributes presented in the database. • Single valued attributes contain on single value. For example: social security number.

• Multi-value attribute may contain more than one values. For example, a person can have more than one phone numbers. Key is an attribute or collection of attributes that uniquely identifies an entity among entity set. Super Key: Set of attributes (one or more) that collectively identifies an entity in an entity set.



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Candidate Key:Minimal super key is called candidate key that is, supers keys for which no proper subset are a superkey. An entity set may have more than one candidate key. Primary Key: This is one of the candidate key chosen by the database designer to uniquely identify the entity set. Relationship The association among entities is called relationship. For example, employee entity has relation works with department. Relationship of similar type is called relationship set. Like entities, a relationship too can have attributes. These attributes are called descriptive attributes. Mapping Cardinality defines the number of entities in one entity set which can be associated to the number of entities of other set via relationship set. One-to-one: one entity from entity set A can be associated with at most one entity of entity set B and vice versa.

shop.ssb cra ck.com One-to-many: One entity from entity set A can be associated with more than one entities of entity set B but from entity set B one entity can be associated with at most one entity.

Many-to-one: More than one entities from entity set A can be associated with at most one entity of entity set B but one entity from entity set B can be associated with more than one entity from entity set A.



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Many-to-many: one entity from A can be associated with more than one entity from B and vice versa.

shop.ssb cra ck.com Relational model In the relational model of a database, all data is represented in terms of tuples, grouped into relations. A database organized in terms of the relational model is a relational database. The purpose of the relational model is to provide a declarative method for specifying data and queries: users directly state what information the database contains and what information they want from it, and let the database management system software take care of describing data structures for storing the data and retrieval procedures for answering queries. Relational algebra is a procedural query language, which takes instances of relations as input and yields instances of relations as output. It uses operators to perform queries. An operator can be either unary or binary. They accept relations as their input and yields relations as their output. Relational algebra is performed recursively on a relation and intermediate results are also considered relations. Fundamental operations of Relational algebra: • Set operators: The relational algebra uses set union, set difference, and Cartesian product from set theory, but adds additional constraints to these operators. For set union and set difference, the two relations involved must be union-compatibleâ that is, the two relations must have the same set of attributes. Because set intersection can be defined in terms of set difference, the two relations involved in set intersection must also be union-compatible.



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Cartesian productis a mathematical operation which returns a set (or product set or simply product) from multiple sets. That is, for sets A and B, the Cartesian product A Ã B is the set of all ordered pairs (a, b) where a â A and b â B. A ◊ B = (a, b) | a Á A and b Á B • Projection ( ): A projection is a unary operation written as a1 ......an where a1 ......an is a set of attribute names. The result of such projection is defined as the set that is obtained when all tuples in R are restricted to the set a1 ......an . • Union Operation (U): Union operation performs binary union between two given relations and is defined as r U s = [t | t Á r or t Á s] • Set Difference ( - ): The result of set difference operation is tuples which present in one relation but are not in the second relation. Notation: r - s • Rename operation ( fl ): Results of relational algebra are also relations but without any name. The rename operation allows us to rename the output relation. rename operation is denoted with small greek letter rho. Notation: fl ◊ (E)

• Tuple: A tuple is an ordered list of elements. In mathematics, an n-tuple is a sequence (or ordered list) of n elements, where n is a non-negative integer. There is only one 0tuple, an empty sequence. An n-tuple is defined inductively using the construction of an ordered pair. Tuples are usually written by listing the elements within parentheses ”( )” and separated by commas.

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Note: The fundamental assumption of the relational model is that all data is represented as mathematical n-ary relations, an n-ary relation being a subset of the Cartesian product of n domains. In the mathematical model, reasoning about such data is done in two-valued predicate logic, meaning there are two possible evaluations for each proposition: either true or false (and in particular no third value such as unknown, or not applicable, either of which are often associated with the concept of NULL). Data are operated upon by means of a relational calculus or relational algebra, these being equivalent in expressive power. The relational model of data permits the database designer to create a consistent, logical representation of information. Consistency is achieved by including declared constraints in the database design, which is usually referred to as the logical schema. The theory includes a process of database normalization whereby a design with certain desirable properties can be selected from a set of logically equivalent alternatives. The access plans and other implementation and operation details are handled by the DBMS engine, and are not reflected in the logical model. This contrasts with common practice for SQL DBMSs in which performance tuning often requires changes to the logical model.

Database design The problem with data is that it changes. Not just its individual items’ values change, but their structure and use, especially when kept over extended periods of time. Even for public records that may have been kept for hundreds of years, there are occasionally changes in what data elements are captured and recorded and how. Therefore, a method to avoid problems due to duplication of data values and modification of structure and content has been developed. This method is called normalization.



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Normalization Normalization is the formalization of the design process of making a database compliant with the concept of a Normal Form. It addresses various ways in which we may look for repeating data values in a table. There are several levels of the Normal Form, and each level requires that the previous level be satisfied. The normalization process is based on collecting an exhaustive list of all data items to be maintained in the database and starting the design with a few ”superset” tables. Theoretically, it may be possible, although not very practical, to start by placing all the attributes in a single table. For best results, start with a reasonable breakdown. First Normal Form (1NF): A table is 1NF if every cell contains a single value, not a list of values. This properties is known as atomic. 1NF also prohibits repeating group of columns such as item1 , item2 , .., itemN . Instead, you should create another table using one-to-many relationship. Second Normal Form (2NF): A table is 2NF, if it is 1NF and every non-key column is fully dependent on the primary key. Furthermore, if the primary key is made up of several columns, every non-key column shall depend on the entire set and not part of it. Third Normal Form (3NF): A table is 3NF, if it is 2NF and the non-key columns are independent of each others. In other words, the non-key columns are dependent on primary key, only on the primary key and nothing else. For example, suppose that we have a Products table with columns product-ID (primary key), name and unit price. The column discount rate shall not belong to Products table if it is also dependent on the unit price, which is not part of the primary key. Boyce/Codd Normal Form: Reduce third normal form entities to Boyce/Codd normal form (BCNF) by ensuring that they are in third normal form for any feasible choice of candidate key as primary key. In short, Boyce/Codd normal form (BCNF) addresses dependencies between columns that are part of a Candidate Key. Some of the normalizations performed above may depend on our choice of the Primary Key. BCNF addresses those cases where applying the normalization rules to a Candidate Key other than the one chosen as the Primary Key would give a different result. In actuality, if we substitute any Candidate Key for Primary Key in 2NF and 3NF, 3NF would be equivalent with BCNF.

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Integrity Rules • Entity Integrity Rule: The primary key cannot contain NULL. Otherwise, it cannot uniquely identify the row. For composite key made up of several columns, none of the column can contain NULL. Most of the RDBMS check and enforce this rule. • Referential Integrity Rule: Each foreign key value must be matched to a primary key value in the table referenced (or parent table). You can insert a row with a foreign key in the child table only if the value exists in the parent table. If the value of the key changes in the parent table (e.g., the row updated or deleted), all rows with this foreign key in the child table(s) must be handled accordingly. You could either (a) disallow the changes; (b) cascade the change (or delete the records) in the child tables accordingly; (c) set the key value in the child tables to NULL. • Business logic Integrity: Beside the above two general integrity rules, there could be integrity (validation) pertaining to the business logic, e.g., zip code shall be 5-digit within a certain ranges, delivery date and time shall fall in the business hours; quantity ordered shall be equal or less than quantity in stock, etc. These could be carried out in validation rule (for the specific column) or programming logic.

Query languages (SQL) SQL is Structured Query Language, which is a computer language for storing, manipulating and retrieving data stored in relational database.



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SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server use SQL as standard database language. When you are executing an SQL command for any RDBMS, the system determines the best way to carry out your request and SQL engine figures out how to interpret the task. There are various components included in the process. These components are Query Dispatcher, Optimization Engines, Classic Query Engine and SQL Query Engine, etc. Classic query engine handles all non-SQL queries but SQL query engine won’t handle logical files.

shop.ssb cra ck.com SQL Actions: • SQL can execute queries against a database • SQL can retrieve data from a database • SQL can insert records in a database

• SQL can update records in a database

• SQL can delete records from a database • SQL can create new databases

• SQL can create new tables in a database

• SQL can create stored procedures in a database • SQL can create views in a database

• SQL can set permissions on tables, procedures, and views



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Important SQL Commands: • SELECT - extracts data from a database

Syntax: SELECT column name,column name FROM table name; also SELECT * FROM table name;

• UPDATE - updates data in a database Syntax: UPDATE table name

SET column1=value1,column2=value2,... WHERE some column=some value; • DELETE - deletes data from a database Syntax: DELETE FROM table name WHERE some column=some value; • INSERT INTO - inserts new data into a database Syntax: INSERT INTO table name VALUES (value1,value2,value3,...); also INSERT INTO table name (column1,column2,column3,...) VALUES (value1,value2,value3,...); • CREATE DATABASE - creates a new database Syntax: CREATE DATABASE dbname;

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• ALTER DATABASE - modifies a database Syntax: ALTER DATABASE dbname;

• CREATE TABLE - creates a new table Syntax: CREATE TABLE table name ( column name1 data type(size), column name2 data type(size), column name3 data type(size), .... ); • ALTER TABLE - modifies a table

Syntax: ALTER TABLE table name ADD column name datatype also ALTER TABLE table name DROP COLUMN column name

• DROP TABLE - deletes a table

Syntax: DROP TABLE table name

• CREATE INDEX - creates an index (search key) Syntax: CREATE INDEX index name ON table name (column name) • DROP INDEX - deletes an index

Syntax: DROP INDEX index name ON table name



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List of important SQL functions • AVG() Function:

The AVG() function returns the average value of a numeric column. SQL AVG() Syntax: SELECT AVG(column name) FROM table name

• SQL COUNT() Function:

The COUNT() function returns the number of rows that matches a specified criteria. SQL COUNT(column name) Syntax: The COUNT(column name) function returns the number of values (NULL values will not be counted) of the specified column: SELECT COUNT(column name) FROM table name; also SQL COUNT(*) Syntax: The COUNT(*) function returns the number of records in a table: SELECT COUNT(*) FROM table name;

• MAX() Function:

The MAX() function returns the largest value of the selected column. SQL MAX() Syntax: SELECT MAX(column name) FROM table name;

• SUM() Function:

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The SUM() function returns the total sum of a numeric column. SQL SUM() Syntax:

SELECT SUM(column name) FROM table name; • UCASE() Function:

The UCASE() function converts the value of a field to uppercase. SQL UCASE() Syntax: SELECT UCASE(column name) FROM table name;

• FORMAT() Function:

The FORMAT() function is used to format how a field is to be displayed. SQL FORMAT() Syntax: SELECT FORMAT(column name,format) FROM table name;

• LEN() Function:

The LEN() function returns the length of the value in a text field. SQL LEN() Syntax: SELECT LEN(column name) FROM table name;

File structures A file is sequence of records stored in binary format. A disk drive is formatted into several blocks, which are capable for storing records. File records are mapped onto those disk blocks.



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File organization methods: • Heap File Organization: When a file is created using Heap File Organization mechanism, the Operating Systems allocates memory area to that file without any further accounting details. File records can be placed anywhere in that memory area. It is the responsibility of software to manage the records. Heap File does not support any ordering, sequencing or indexing on its own. • Sequential File Organization: Every file record contains a data field (attribute) to uniquely identify that record. In sequential file organization mechanism, records are placed in the file in the some sequential order based on the unique key field or search key. Practically, it is not possible to store all the records sequentially in physical form. • Hash File Organization: This mechanism uses a Hash function computation on some field of the records. As we know, that file is a collection of records, which has to be mapped on some block of the disk space allocated to it. This mapping is defined that the hash computation. The output of hash determines the location of disk block where the records may exist. • Clustered File Organization: Clustered file organization is not considered good for large databases. In this mechanism, related records from one or more relations are kept in a same disk block, that is, the ordering of records is not based on primary key or search key. This organization helps to retrieve data easily based on particular join condition. Other than particular join condition, on which data is stored, all queries become more expensive. Sequential files A sequential file is the most primitive of all file structures. It has no directory and no linking pointers. The records are generally organised in lexicographic order on the value of some key. In other words, a particular attribute is chosen whose value will determine the order of the records. Sometimes when the attribute value is constant for a large number of records a second key is chosen to give an order when the first key fails to discriminate. Advantages:

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• Easy to implement

• Provides fast access to the next record using lexicographic order. Disadvantages:

• Difficult to update - inserting a new record may require moving a large proportion of the file • Random access is extremely slow Indexing sequential files Indexing is a data structure technique to efficiently retrieve records from database files based on some attributes on which the indexing has been done. Indexing is defined based on its indexing attributes. Indexing can be one of the following types: 1. Primary Index: If index is built on ordering ’key-field’ of file it is called Primary Index. Generally it is the primary key of the relation. 2. Secondary Index: If index is built on non-ordering field of file it is called Secondary Index. 3. Clustering Index: If index is built on ordering non-key field of file it is called Clustering Index.



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Ordering field is the field on which the records of file are ordered. It can be different from primary or candidate key of a file. There types are - Sparse index and dense index. In sparse index, index records are not created for every search key. An index record here contains search key and actual pointer to the data on the disk. In dense index, there is an index record for every search key value in the database. This makes searching faster but requires more space to store index records itself. Index record contains search key value and a pointer to the actual record on the disk. Multilevel Index Index records are comprised of search-key value and data pointers. This index itself is stored on the disk along with the actual database files. As the size of database grows so does the size of indices. There is an immense need to keep the index records in the main memory so that the search can speed up. If single level index is used then a large size index cannot be kept in memory as whole and this leads to multiple disk accesses.Multi-level Index helps breaking down the index into several smaller indices in order to make the outer most level so small that it can be saved in single disk block which can easily be accommodated anywhere in the main memory. B + Tree B tree is multi-level index format, which is balanced binary search trees. As mentioned earlier single level index records becomes large as the database size grows, which also degrades performance. All leaf nodes of B+ tree denote actual data pointers. B + tree ensures that all leaf nodes remain at the same height, thus balanced. Additionally, all leaf nodes are linked using link list, which makes B+ tree to support random access as well as sequential access.

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Structure of B +

Every leaf node is at equal distance from the root node. A B + tree is of order n where n is fixed for every B + tree.

Internal nodes: • Internal (non-leaf) nodes contains at least â

n/2â

pointers, except the root node.

• At most, internal nodes contain n pointers. Leaf nodes: • Leaf nodes contain at least â

n/2â

record pointers and â

n/2â

key values

• At most, leaf nodes contain n record pointers and n key values

• Every leaf node contains one block pointer P to point to next leaf node and forms a linked list.



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Inserting B + Tree If leaf node overflows: • Split node into two parts

• Partition at i = [(m+1)/2]

• First i entries are stored in one node

• Rest of the entries (i+1 onwards) are moved to a new node • i th key is duplicated in the parent of the leaf If non-leaf node overflows: • Split node into two parts

• Partition the node at i = â

(m+1)/2â

• Entries upto i are kept in one node

• Rest of the entries are moved to a new node

Transactions and concurrency control A transaction can be defined as a group of tasks. A single task is the minimum processing unit of work, which cannot be divided further. ACID Properties

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A transaction may contain several low level tasks and further a transaction is very small unit of any program. A transaction in a database system must maintain some properties in order to ensure the accuracy of its completeness and data integrity. These properties are refer to as ACID properties and are mentioned below: • Atomicity: Though a transaction involves several low level operations but this property states that a transaction must be treated as an atomic unit, that is, either all of its operations are executed or none. There must be no state in database where the transaction is left partially completed. States should be defined either before the execution of the transaction or after the execution/abortion/failure of the transaction. • Consistency: This property states that after the transaction is finished, its database must remain in a consistent state. There must not be any possibility that some data is incorrectly affected by the execution of transaction. If the database was in a consistent state before the execution of the transaction, it must remain in consistent state after the execution of the transaction. • Durability: This property states that in any case all updates made on the database will persist even if the system fails and restarts. If a transaction writes or updates some data in database and commits that data will always be there in the database. If the transaction commits but data is not written on the disk and the system fails, that data will be updated once the system comes up. • Isolation: In a database system where more than one transaction are being executed simultaneously and in parallel, the property of isolation states that all the transactions will be carried out and executed as if it is the only transaction in the system. No transaction will affect the existence of any other transaction.



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States of Transactions A transaction in a database can be in one of the following state:

• Active: In this state the transaction is being executed. This is the initial state of every transaction. • Partially Committed: When a transaction executes its final operation, it is said to be in this state. After execution of all operations, the database system performs some checks e.g. the consistency state of database after applying output of transaction onto the database. • Failed: If any checks made by database recovery system fails, the transaction is said to be in failed state, from where it can no longer proceed further.

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• Aborted: If any of checks fails and transaction reached in Failed state, the recovery manager rolls back all its write operation on the database to make database in the state where it was prior to start of execution of transaction. Transactions in this state are called aborted. Database recovery module can select one of the two operations after a transaction aborts - Re-start the transaction and kill the transaction. • Committed: If transaction executes all its operations successfully it is said to be committed. All its effects are now permanently made on database system.

Concurrency control In a multiprogramming environment where more than one transactions can be concurrently executed, there exists a need of protocols to control the concurrency of transaction to ensure atomicity and isolation properties of transactions. Concurrency control protocols, which ensure serializability of transactions, are most desirable. Concurrency control protocols can be broadly divided into two categories: • Lock based protocols

• Time stamp based protocols Lock based protocols Database systems, which are equipped with lock-based protocols, use mechanism by which any transaction cannot read or write data until it acquires appropriate lock on it first. Locks are of two kinds: • Binary Locks: a lock on data item can be in two states; it is either locked or unlocked.



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• Shared/exclusive: this type of locking mechanism differentiates lock based on their uses. If a lock is acquired on a data item to perform a write operation, it is exclusive lock. Because allowing more than one transactions to write on same data item would lead the database into an inconsistent state. Read locks are shared because no data value is being changed. There are four types lock protocols available: • Simplistic: Simplistic lock based protocols allow transaction to obtain lock on every object before ’write’ operation is performed. As soon as ’write’ has been done, transactions may unlock the data item. • Pre-claiming: In this protocol, a transactions evaluations its operations and creates a list of data items on which it needs locks. Before starting the execution, transaction requests the system for all locks it needs beforehand. If all the locks are granted, the transaction executes and releases all the locks when all its operations are over. Else if all the locks are not granted, the transaction rolls back and waits until all locks are granted.

• Two phase locking: This locking protocol is divides transaction execution phase into three parts. In the first part, when transaction starts executing, transaction seeks grant for locks it needs as it executes. Second part is where the transaction acquires all locks and no other lock is required. Transaction keeps executing its operation. As soon as the transaction releases its first lock, the third phase starts. In this phase a transaction cannot demand for any lock but only releases the acquired locks.

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• Strict two phase locking: The first phase of Strict-2PL is same as 2PL. After acquiring all locks in the first phase, transaction continues to execute normally. But in contrast to 2PL, Strict-2PL does not release lock as soon as it is no more required, but it holds all locks until commit state arrives. Strict-2PL releases all locks at once at commit point.



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Time stamp based protocols The most commonly used concurrency protocol is time-stamp based protocol. This protocol uses either system time or logical counter to be used as a time-stamp. Lock based protocols manage the order between conflicting pairs among transaction at the time of execution whereas time-stamp based protocols start working as soon as transaction is created. Every transaction has a time-stamp associated with it and the ordering is determined by the age of the transaction. A transaction created at 0002 clock time would be older than all other transaction, which come after it. For example, any transaction ’y’ entering the system at 0004 is two seconds younger and priority may be given to the older one. In addition, every data item is given the latest read and write-timestamp. This lets the system know, when was last read and write operation made on the data item.

3

Software engineering

Information gathering The Information system designed for an organization must meet the requirements of the end users of the organization. To obtain what an end user expects from the Information System the designer must gain complete knowledge of the organization’s working. It is important for the student to know the information gathering techniques so that no information is overlooked and the nature and functions of an organization are clearly understood. The main purpose of gathering information is to determine the information requirements of an organization. Information requirements are often not stated precisely by management.

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Information gathering strategies and sources

A strategy should be evolved by the analyst to gather information. The strategy consists of identifying information sources, evolving a method of obtaining information from the identified sources and using an information flow model of organization The main sources of information are users of the system, forms and documents used in the organization, procedure manuals, rule books etc, reports used by the organization and existing computer programs. Methods of Information gathering • Searching for information: Information can be gathered by interviewing top-level management, middle level management and operational staff. Besides Interviews group discussions also help the analyst to gather information. It is not possible to obtain all information in a single interview, more than one interview is thus required. • Planning and interview: Before starting the interview the analyst must make a list of people to be interviewed and in what order, plan and note down a list of questions to be asked, plan several interviews with same person-mainly to clarify doubts and interview groups as appropriate. • Questionnaires: are useful for collecting statistical data. Sometimes the questionnaires are not promptly replied and several follow-ups/personal interviews may be required to get questionnaires back from respondents But if the questionnaires are short the probability of getting the reply is high When data has to be collected form large number of people questionnaires are useful. • Task analysis: Team of engineers and developers may analyze the operation for which the new system is required. If the client already has some software to perform certain operation, it is studied and requirements of proposed system are collected.



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• Domain analysis: Every software falls into some domain category. The expert people in the domain can be a great help to analyze general and specific requirements. Brainstorming: An informal debate is held among various stakeholders and all their inputs are recorded for further requirements analysis. Prototyping: Prototyping is building user interface without adding detail functionality for user to interpret the features of intended software product. It helps giving better idea of requirements. If there is no software installed at clientâ ès end for developerâ ès reference and the client is not aware of its own requirements, the developer creates a prototype based on initially mentioned requirements. The prototype is shown to the client and the feedback is noted. The client feedback serves as an input for requirement gathering. • Observation: Team of experts visit the clientâ ès organization or workplace. They observe the actual working of the existing installed systems. They observe the workflow at clientâ ès end and how execution problems are dealt. The team itself draws some conclusions which aid to form requirements expected from the software.

Requirement and feasibility analysis Requirements analysis is a software engineering task that bridges the gap between system level requirements engineering and software design

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Software requirements analysis may be divided into five areas of effort: (1) problem recognition, (2) evaluation and synthesis, (3) modeling (4) specification, and (5) review. Analysis methods are related by a set of operational principles: • The information domain of a problem must be represented and understood. • The functions that the software is to perform must be defined.

• The behavior of the software (as a consequence of external events) must be represented.

• The models that depict information, function, and behavior must be partitioned in a manner that uncovers detail in a layered (or hierarchical) fashion. • The analysis process should move from essential information toward implementation detail



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Modeling Functional models: Software transforms information, and in order to accomplish this, it must perform at least three generic functions: input, processing, and output. When functional models of an application are created, the software engineer focuses on problem specific functions. The functional model begins with a single context level model (i.e., the name of the software to be built). Over a series of iterations, more and more functional detail is provided, until a thorough delineation of all system functionality is represented. Behavioral models: Most software responds to events from the outside world. This stimulus/response characteristic forms the basis of the behavioral model. A computer program always exists in some state, an externally observable mode of behavior (e.g., waiting, computing, printing, polling) that is changed only when some event occurs. For example, software will remain in the wait state until (1) an internal clock indicates that some time interval has passed, (2) an external event (e.g., a mouse movement) causes an interrupt, or (3) an external system signals the software to act in some manner. A behavioral model creates a representation of the states of the software and the events that cause a software to change state. Models created during requirements analysis serve a number of important roles: • The model aids the analyst in understanding the information, function, and behavior of a system, thereby making the requirements analysis task easier and more systematic. • The model becomes the focal point for review and, therefore, the key to a determination of completeness, consistency, and accuracy of the specifications. • The model becomes the foundation for design, providing the designer with an essential representation of software that can be ”mapped” into an implementation context. Partitioning

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Problems are often too large and complex to be understood as a whole. For this reason, we tend to partition (divide) such problems into parts that can be easily understood and establish interfaces between the parts so that overall function can be accomplished. The fourth operational analysis principle suggests that the information, functional, and behavioral domains of software can be partitioned. In essence, partitioning decomposes a problem into its constituent parts. Conceptually, we establish a hierarchical representation of function or information and then partition the uppermost element by (1) exposing increasing detail by moving vertically in the hierarchy or (2) functionally decomposing the problem by moving horizontally in the hierarchy. Feasibility analysis Information systems development projects are usually subjected to one or more feasibility analyses prior to and during their life. In an information systems development project context, feasibility is the measure of how beneficial the development or enhancement of an information system would be to the business. Feasibility analysis is the process by which feasibility is measured. Information systems development projects are subjected to at least three interrelated feasibility types-operational feasibility, technical feasibility, and economic feasibility. • Operational feasibility is the measure of how well particular information systems will work in a given environment. • Technical feasibility is the measure of the practicality of a specific technical information system solution and the availability of technical resources. • Economic feasibility is the measure of the cost-effectiveness of an information system solution.



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Data flow diagram Data flow diagram is graphical representation of flow of data in an information system. It is capable of depicting incoming data flow, outgoing data flow and stored data. The DFD does not mention anything about how data flows through the system. There is a prominent difference between DFD and Flowchart. The flowchart depicts flow of control in program modules. DFDs depict flow of data in the system at various levels. DFD does not contain any control or branch elements. Data Flow Diagrams are either Logical or Physical: • Logical DFD - This type of DFD concentrates on the system process, and flow of data in the system.For example in a Banking software system, how data is moved between different entities. • Physical DFD - This type of DFD shows how the data flow is actually implemented in the system. It is more specific and close to the implementation. DFD Components:

• Entities: Entities are source and destination of information data. Entities are represented by a rectangles with their respective names.

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• Process: Activities and action taken on the data are represented by Circle or Roundedged rectangles. • Data Storage: There are two variants of data storage - it can either be represented as a rectangle with absence of both smaller sides or as an open-sided rectangle with only one side missing. • Data Flow: Movement of data is shown by pointed arrows. Data movement is shown from the base of arrow as its source towards head of the arrow as destination. Levels of DFD • Level 0: Highest abstraction level DFD is known as Level 0 DFD, which depicts the entire information system as one diagram concealing all the underlying details. Level 0 DFDs are also known as context level DFDs.



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• Level 1: The Level 0 DFD is broken down into more specific, Level 1 DFD. Level 1 DFD depicts basic modules in the system and flow of data among various modules. Level 1 DFD also mentions basic processes and sources of information.

• Level 2: At this level, DFD shows how data flows inside the modules mentioned in Level 1. Higher level DFDs can be transformed into more specific lower level DFDs with deeper level of understanding unless the desired level of specification is achieved.

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Structure Charts

Structure chart is a chart derived from Data Flow Diagram. It represents the system in more detail than DFD. It breaks down the entire system into lowest functional modules, describes functions and sub-functions of each module of the system to a greater detail than DFD. Symbols used in construction of structure charts: • Module: It represents process or subroutine or task. A control module branches to more than one sub-module. Library Modules are re-usable and invokable from any module.

• Condition: It is represented by small diamond at the base of module. It depicts that control module can select any of sub-routine based on some condition.



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• Jump: An arrow is shown pointing inside the module to depict that the control will jump in the middle of the sub-module.

• Loop: A curved arrow represents loop in the module. All sub-modules covered by loop repeat execution of module.

shop.ssb cra ck.com • Data flow: A directed arrow with empty circle at the end represents data flow.

• Control flow: A directed arrow with filled circle at the end represents control flow.



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input/output design • Architectural design

The architectural design of a system emphasizes on the design of the systems architecture which describes the structure, behavior, and more views of that system.

• Logical design

The logical design of a system pertains to an abstract representation of the data flows, inputs and outputs of the system. This is often conducted via modelling, using an overabstract (and sometimes graphical) model of the actual system. In the context of systems design are included. Logical design includes ER Diagrams i.e. Entity Relationship Diagrams.

• Physical design

The physical design relates to the actual input and output processes of the system. This is laid down in terms of how data is input into a system, how it is verified/authenticated, how it is processed, and how it is displayed as In Physical design, the following requirements about the system are decided. 1. Input requirement 2. Output requirements 3. Storage requirements 4. Processing Requirements 5. System control and backup or recovery.

Coding

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Coding is also known as programming phase. The implementation of software design starts in terms of writing program code in the suitable programming language and developing error-free executable programs efficiently.

Testing An estimate says that 50 percentage of whole software development process should be tested. Errors may ruin the software from critical level to its own removal. Software testing is done while coding by the developers and thorough testing is conducted by testing experts at various levels of code such as module testing, program testing, product testing, in-house testing and testing the product at user’s end. Early discovery of errors and their remedy is the key to reliable software.

Integration Software may need to be integrated with the libraries, databases and other program(s). This stage of SDLC is involved in the integration of software with outer world entities.

Implementation This means installing the software on user machines. At times, software needs post-installation configurations at user end. Software is tested for portability and adaptability and integration related issues are solved during implementation.



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Operation and Maintenance This phase confirms the software operation in terms of more efficiency and less errors. If required, the users are trained on, or aided with the documentation on how to operate the software and how to keep the software operational. The software is maintained timely by updating the code according to the changes taking place in user end environment or technology. This phase may face challenges from hidden bugs and real-world unidentified problems.

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Programming in C

The C is a general-purpose, procedural, imperative computer programming language developed in 1972 by Dennis M. Ritchie at the Bell Telephone Laboratories to develop the UNIX operating system. The C is the most widely used computer language, it keeps fluctuating at number one scale of popularity along with Java programming language, which is also equally popular and most widely used among modern software programmers. C was adopted as a system development language because it produces code that runs nearly as fast as code written in assembly language. Some examples of the use of C might be: • Operating Systems

• Language Compilers • Assemblers

• Text Editors

• Print Spoolers

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• Network Drivers

• Modern Programs • Databases Basic syntax • Tokens in C

A C program consists of various tokens and a token is either a keyword, an identifier, a constant, a string literal, or a symbol. For example, the following C statement consists of five tokens:

• Semicolons (;)

In C program, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.

• Comments

Comments are like helping text in your C program and they are ignored by the compiler. They start with /* and terminates with the characters */.

• Identifiers

A C identifier is a name used to identify a variable, function, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore followed by zero or more letters, underscores, and digits (0 to 9).

• Keyword

Keyword are the reserved words may not be used as constant or variable or any other identifier names.



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Data types • Basic Types: They are arithmetic types and consists of the two types: (1) integer types and (2) floating-point types. Following table gives you details about standard Integer types with its storage sizes and value ranges:

shop.ssb cra ck.com Following table gives you details about standard Floating-point types with storage sizes and value ranges and their precision:

• Enumerated types: They are again arithmetic types and they are used to define variables that can only be assigned certain discrete integer values throughout the program.



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• Void: The type specifier void indicates that no value is available.

The void type specifies that no value is available. It is used in three kinds of situations: – Function returns as void: There are various functions in C which do not return value or you can say they return void. A function with no return value has the return type as void. For example void exit (int status) – Function arguments as void: There are various functions in C which do not accept any parameter. A function with no parameter can accept as a void. For example, int rand(void) – Pointers to void: A pointer of type void * represents the address of an object, but not its type. For example a memory allocation function void *malloc( size t size ); returns a pointer to void which can be casted to any data type.

• Derived types: They include (1) Pointer types, (2) Array types, (3) Structure types, (4) Union types and (5) Function types. Variable A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C has a specific type, which determines the size and layout of the variable’s memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable. The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because C is case-sensitive. Based on the basic types explained in previous chapter, there will be the following basic variable types:

shop.ssb cra ck.com Constants The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well. The constants are treated just like regular variables except that their values cannot be modified after their definition. There are two simple ways in C to define constants: 1. Using # define preprocessor. 2. Using const keyword. C Operators An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C language is rich in built-in operators and provides the following types of operators: • Arithmetic Operators

Following table shows all the arithmetic operators supported by C language. Assume variable A holds 10 and variable B holds 20 then:



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• Relational Operators

Following table shows all the relational operators supported by C language. Assume variable A holds 10 and variable B holds 20, then:

shop.ssb cra ck.com • Logical Operators

Following table shows all the logical operators supported by C language. Assume variable A holds 1 and variable B holds 0, then:

• Bitwise Operators

Bitwise operator works on bits and perform bit-by-bit operation. The truth tables for &, |, and ·.



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• Assignment Operators

There are following assignment operators supported by C language:

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• Misc Operators

There are few other important operators including sizeof and ? : supported by C Language.

Decision making C programming language provides following types of decision making statements. Information Technology


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Loops C programming language provides the following types of loop to handle looping requirements.

Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.

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• Break statement: Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch. • Continue statement: Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating. • goto statement: Transfers control to the labeled statement. Though it is not advised to use goto statement in your program. Function A function is a group of statements that together perform a task. Every C program has at least one function, which is main(), and all the most trivial programs can define additional functions. A function declaration tells the compiler about a function’s name, return type, and parameters. A function definition provides the actual body of the function. A function definition in C programming language consists of a function header and a function body. Here are all the parts of a function: • Return Type: A function may return a value. The return type is the data type of the value the function returns. Some functions perform the desired operations without returning a value. In this case, the return type is the keyword void. • Function Name: This is the actual name of the function. The function name and the parameter list together constitute the function signature. Parameters: A parameter is like a place holder. When a function is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. The parameter list refers to the type, order, and number of the parameters of a function. Parameters are optional; that is, a function may contain no parameters. • Function Body: The function body contains a collection of statements that define what the function does.



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Object-oriented programming

Object-oriented programming (OOP) is a programming paradigm based on the concept of ”objects”, which are data structures that contain data, in the form of fields, often known as attributes; and code, in the form of procedures, often known as methods. A distinguishing feature of objects is that an object’s procedures can access and often modify the data fields of the object with which they are associated (objects have a notion of ”this”). In object-oriented programming, computer programs are designed by making them out of objects that interact with one another. Object An object can be considered a ”thing” that can perform a set of related activities. The set of activities that the object performs defines the object’s behavior. For example, the Hand (object) can grip something, or a Student (object) can give their name or address. Class A class is simply a representation of a type of object. It is the blueprint, or plan, or template, that describes the details of an object. A class is the blueprint from which the individual objects are created. Class is composed of three things: a name, attributes, and operations. Encapsulation The encapsulation is the inclusion-within a program object-of all the resources needed for the object to function, basically, the methods and the data. In OOP the encapsulation is mainly achieved by creating classes, the classes expose public methods and properties. A class is kind of a container or capsule or a cell, which encapsulate a set of methods, attribute and properties to provide its indented functionalities to other classes. In that sense, encapsulation also allows a class to change its internal implementation without hurting the overall functioning of the system. That idea of encapsulation is to hide how a class does its business, while allowing other classes to make requests of it.

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Association Association is a (*a*) relationship between two classes. It allows one object instance to cause another to perform an action on its behalf. Association is the more general term that define the relationship between two classes, where as the aggregation and composition are relatively special. Difference between Association, Aggregation, and Composition: Association is a *has-a* relationship between two classes where there is no particular ownership in place. It is just the connectivity between the two classes. When you define a variable of one class in another class, you enable first to associate functions and properties of the second class. Then again both Aggregation and Composition are types of Association. Aggregation is a weak type of Association with partial ownership. For an Aggregation relationship, we use the term *uses* to imply a weak *has-a* relationship. This is weak compared to Composition. Then again, weak meaning the linked components of the aggregator may survive the aggregations life-cycle without the existence of their parent objects. For example, a school department *uses* teachers. Any teacher may belong to more than one department. And so, if a department ceases to exist, the teacher will still exist. On the other hand, Composition is a strong type of Association with full ownership. This is strong compared to the weak Aggregation. For a Composition relationship, we use the term *owns* to imply a strong *has-a* relationship. For example, a department *owns* courses, which means that the any course’s life-cycle depends on the department’s life-cycle. Hence, if a department ceases to exist, the underlying courses will cease to exist as well. Whenever there is no ownership in place, we regard such a relationship as just an Association and we simply use the *has-a* term, or sometimes the verb describing the relationship. For



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example, a teacher *has-a* or *teaches* a student. There is no ownership between the teacher and the student, and each has their own life-cycle. Abstraction and generalization Abstraction is an emphasis on the idea, qualities and properties rather than the particulars (a suppression of detail). The importance of abstraction is derived from its ability to hide irrelevant details and from the use of names to reference objects. Abstraction is essential in the construction of programs. It places the emphasis on what an object is or does rather than how it is represented or how it works. Thus, it is the primary means of managing complexity in large programs. While abstraction reduces complexity by hiding irrelevant detail, generalization reduces complexity by replacing multiple entities which perform similar functions with a single construct. Generalization is the broadening of application to encompass a larger domain of objects of the same or different type. Programming languages provide generalization through variables, parameterization, generics and polymorphism. It places the emphasis on the similarities between objects. Thus, it helps to manage complexity by collecting individuals into groups and providing a representative which can be used to specify any individual of the group. What is an Interface In summary the Interface separates the implementation and defines the structure, and this concept is very useful in cases where you need the implementation to be interchangeable. Apart from that an interface is very useful when the implementation changes frequently. Some say you should define all classes in terms of interfaces, but I think recommendation seems a bit extreme. Interface can be used to define a generic template and then one or more abstract classes to define partial implementations of the interface. Interfaces just specify the method declaration (implicitly public and abstract) and can contain properties (which are also implicitly public and abstract). Interface definition begins with the keyword interface. An interface like that of an abstract class cannot be instantiated. If a class that implements an interface does not define all the methods of the interface, then it must be declared abstract and the method definitions must be provided by the subclass that extends the abstract class. In addition to this an interfaces can inherit other interfaces.

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Polymorphism Polymorphisms is a generic term that means ’many shapes’. More precisely Polymorphisms means the ability to request that the same operations be performed by a wide range of different types of things. At times, I used to think that understanding Object Oriented Programming concepts have made it difficult since they have grouped under four main concepts, while each concept is closely related with one another. Hence one has to be extremely careful to correctly understand each concept separately, while understanding the way each related with other concepts. Method and operator Overloading Method overloading is the ability to define several methods all with the same name. The operator overloading (less commonly known as ad-hoc polymorphisms) is a specific case of polymorphisms in which some or all of operators like +, - or == are treated as polymorphic functions and as such have different behaviors depending on the types of its arguments. Method Overriding Method overriding is a language feature that allows a subclass to override a specific implementation of a method that is already provided by one of its super-classes. A subclass can give its own definition of methods but need to have the same signature as the method in its super-class. This means that when overriding a method the subclass’s method has to have the same name and parameter list as the super-class’ overridden method.



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Class Diagram Class diagrams are widely used to describe the types of objects in a system and their relationships. Class diagrams model class structure and contents using design elements such as classes, packages and objects. Class diagrams describe three different perspectives when designing a system, conceptual, specification, and implementation. These perspectives become evident as the diagram is created and help solidify the design. The Class diagrams, physical data models, along with the system overview diagram are in my opinion the most important diagrams that suite the current day rapid application development requirements. UML notations:

Package diagrams are used to reflect the organization of packages and their elements. When used to represent class elements, package diagrams provide a visualization of the namespaces. In my designs, I use the package diagrams to organize classes in to different modules of the system. Sequence diagrams model the flow of logic within a system in a visual manner, it enable both to document and validate your logic, and are used for both analysis and design purposes. Sequence diagrams are the most popular UML artifact for dynamic modeling, which focuses on identifying the behavior within your system.

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Gang of Four (GoF) Design Patterns The Gang of Four (GoF) patterns are generally considered the foundation for all other patterns. They are categorized in three groups: Creational, Structural, and Behavioral. Here you will find information on these important patterns. 1. Creational Patterns • Abstract Factory Creates an instance of several families of classes • Builder Separates object construction from its representation

• Factory Method Creates an instance of several derived classes • Prototype A fully initialized instance to be copied or cloned • Singleton A class of which only a single instance can exist 2. Structural Patterns • Adapter Match interfaces of different classes

• Bridge Separates an objectâ ès interface from its implementation • Composite A tree structure of simple and composite objects • Decorator Add responsibilities to objects dynamically

• Facade A single class that represents an entire subsystem Information Technology


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• Flyweight A fine-grained instance used for efficient sharing • Proxy An object representing another object 3. Behavioral Patterns • Chain of Resp. A way of passing a request between a chain of objects • Command Encapsulate a command request as an object

• Interpreter A way to include language elements in a program • Iterator Sequentially access the elements of a collection

• Mediator Defines simplified communication between classes • Memento Capture and restore an object’s internal state

• Observer A way of notifying change to a number of classes • State Alter an object’s behavior when its state changes

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Information'Technology'MCQs'

Information*Technology*MCQs* * Operating*System*

! 1.'''The'part'of'machine'level'instruction,'which'tells'the'central'processor'what'has'to' be'done,'is' (a)' Operation'code' (b)' Address' (c)' Locator' (d)' FlipGFlop' ' 2.'''To'avoid'the'race'condition,'the'number'of'processes'that'may'be'simultaneously' inside'their'critical'section'is' (a)' 8' (b)' 1' (c)' 16' (d)' 0' ' 3.''A'system'program'that'combines'the'separately'compiled'modules'of'a'program'into' a'form'suitable'for'execution' (a)' assembler' (b)' linking'loader' (c)' cross'compiler' (d)' load'and'go' ' 4.'''The'strategy'of'allowing'processes'that'are'logically'runnable'to'be'temporarily' suspended'is'called' (a)' preemptive'scheduling' (b)' non'preemptive'scheduling' (c)' shortest'job'first' (d)' first'come'first'served' ' 5.'''Which'of'the'following'systems'software'does'the'job'of'merging'the'records'from' two'files'into'one?' Security'software' (a)' Utility'program' (b)' Networking'software' (c)' Documentation'system' (d)' None'of'the'above' ' 6.'''Fork'is' (a)' the'dispatching'of'a'task' (b)' the'creation'of'a'new'job' (c)' the'creation'of'a'new'process' (d)' increasing'the'priority'of'a'task' ' 7.'''Thrashing' (a)' is'a'natural'consequence'of'virtual' (b)' can'always'be'avoided'by'swapping' memory'systems' (c)' always'occurs'on'large'computers' (d)' can'be'caused'by'poor'paging' algorithms' ' '


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8.'''Which'of'the'following'instruction'steps,'would'be'written'within'the'diamondG shaped'box,'of'a'flowchart?' (a)' S'='B'G'C' (b)' IS'A<10' (c)' PRINT'A' (d)' DATA'X,4Z' ' 9.'''Which'of'the'following'addressing'modes,'facilitates'access'to'an'operand'whose' location'is'defined'relative'to'the'beginning'of'the'data'structure'in'which'it'appears?' (a)' ascending' (b)' sorting' (c)' index' (d)' indirect' ' 10.''While'running'DOS'on'a'PC,'which'command'would'be'used'to'duplicate'the'entire' diskette?' COPY' (a)' DISKCOPY' (b)' CHKDSK' (c)' TYPE' (d)' ' ' ' ' 11.''What'is'the'name'given'to'the'organized'collection'of'software'that'controls'the' overall'operation'of'a'computer?' (a)' Working'system' (b)' Peripheral'system' (c)' Operating'system' (d)' Controlling'system' ' 12.''The'principle'of'locality'of'reference'justifies'the'use'of' (a)' reenterable' (b)' non'reusable' (c)' virtual'memory' (d)' cache'memory' ' 13.'The'register'or'main'memory'location'which'contains'the'effective'address'of'the' operand'is'known'as' (a)' pointer' (b)' indexed'register' (c)' special'location' (d)' scratch'pad' ' 14.''Resolution'of'externally'defined'symbols'is'performed'by' (a)' Linker' (b)' Loader' (c)' Compiler' (d)' Assembler' ' 15.'Which'of'the'following'are(is)'Language'Processor(s)' (a)' assembles' (b)' compilers' (c)' interpreters' (d)' All'of'the'above' ' '


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16.'In'which'addressing'mode'the'effective'address'of'the'operand'is'the'contents'of'a' register'specified'in'the'instruction'and'after'accessing'the'operand,'the'contents'of'this' register'is'incremented'to'point'to'the'next'item'in'the'list?' (a)' index'addressing' (b)' indirect'addressing' (c)' auto'increment' (d)' auto'decrement' ' 17.'The'memory'allocation'scheme'subject'to'"external"'fragmentation'is' (a)' segmentation' (b)' swapping' (c)' pure'demand'paging' (d)' multiple'contiguous'fixed'partitions' ' 18.'While'working'with'MSGDOS,'which'command'will'you'use'to'transfer'a'specific'file' from'one'disk'to'another?' (a)' DISKCOPY' (b)' COPY' (c)' RENAME' (d)' FORMAT' ' 19.'What'is'the'name'of'the'operating'system'for'the'laptop'computer'called'MacLite?' Windows' (a)' DOS' (b)' MSGDOS' (c)' OZ' (d)' ' ' 20.'What'is'the'name'given'to'the'values'that'are'automatically'provided'by'software'to' reduce'keystrokes'and'improve'a'computer'user's'productivity?' (a)' Defined'values' (b)' Fixed'values' (c)' Default'values' (d)' Special'values' ' 21.'An'algorithm'is'best'described'as' (a)' A'computer'language' (b)' A'step'by'step'procedure'for'solving'a' problem' (c)' A'branch'of'mathematics' (d)' All'of'the'above' ' 22.'The'process'of'transferring'data'intended'for'a'peripheral'device'into'a'disk'(or' intermediate'store)'so'that'it'can'be'transferred'to'peripheral'at'a'more'convenient' time'or'in'bulk,'is'known'as' (a)' multiprogramming' (b)' spooling' (c)' caching' (d)' virtual'programming' ' 23.'The'action'of'parsing'the'source'program'into'the'proper'syntactic'classes'is'known' as' (a)' syntax'analysis' (b)' lexical'analysis' (c)' interpretation'analysis' (d)' general'syntax'analysis' '


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' 24.'Which'of'the'following'is'false'about'disk'when'compared'to'main'memory?' (a)' nonGvolatile' (b)' longer'storage'capacity' (c)' lower'price'per'bit' (d)' faster' ' 25.'Producer'consumer'problem'can'be'solved'using' (a)' semaphores' (b)' event'counters' (c)' monitors' (d)' all'of'the'above' ' 26.'Which'is'a'permanent'database'in'the'general'model'of'compiler?' (a)' Literal'Table' (b)' Identifier'Table' (c)' Terminal'Table' (d)' Source'code' ' 27.'What'is'the'name'of'the'technique'in'which'the'operating'system'of'a'computer' executes'several'programs'concurrently'by'switching'back'and'forth'between'them?' (a)' Partitioning' (b)' Multitasking' (c)' Windowing' (d)' Paging' ' 28.'Software'that'measures,'monitors,'analyzes,'and'controls'realGworld'events'is'called:' (a)' system'software' (b)' realGtime'software' (c)' scientific'software' (d)' business'software' ' 29.'The'details'of'all'external'symbols'and'relocation'formation'(relocation'list'or'map)' is'provided'to'linker'by' (a)' Macro'processor' (b)' Translator' (c)' Loader' (d)' Editor' ' 30.'What'problem'is'solved'by'Dijkstra's'banker's'algorithm?' (a)' mutual'exclusion' (b)' deadlock'recovery' (c)' deadlock'avoidance' (d)' cache'coherence' ' 31.'System'programs'such'as'Compilers'are'designed'so'that'they'are' (a)' reenterable' (b)' non'reusable' (c)' serially'usable' (d)' recursive' ' 32.'A'disk'scheduling'algorithm'in'an'operating'system'causes'the'disk'arm'to'move'back' and'forth'across'the'disk'surface'in'order'to'service'all'requests'in'its'path.'This'is'a' (a)' First'come'first'served' (b)' Shortest'Seek'Time'First'(SSTE)' (c)' Scan' (d)' FIFO' ' '


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33.'What'is'the'name'given'to'the'process'of'initializing'a'microcomputer'with'its' operating'system?' (a)' Cold'booting' (b)' Booting' (c)' Warm'booting' (d)' Boot'recording' ! ' 34.'Which'of'the'following'is'a'type'of'systems'software'used'on'microcomputers?' (a)' MSGDOS' (b)' PCGDOS' (c)' Unix' (d)' All'of'the'above' ' 35.'Operating'system'is' (a)' A'collection'of'hardware' (b)' A'collection'of'inputGoutput'devices' components' (c)' A'collection'of'software'routines' (d)' All'of'the'above' ' 36.'What'is'the'name'given'to'the'software'which'can'be'legally'compiled'and'often' used'for'free?' (a)' Shareware'program' (b)' Public'domain'program' (c)' Firmware'program' (d)' Mindware' ' 37.''Which'of'the'following'is'a'block'device' (a)' mouse' (b)' printer' (c)' terminals' (d)' disk' ' 38.'Which'of'the'following'software'types'is'used'to'simplify'using'systems'software?' (a)' spreadsheet' (b)' operating'environment' (c)' timesharing' (d)' multitasking' ' 39.'The'computational'technique'used'to'compute'the'disk'storage'address'of'individual' records'is'called:' (a)' bubble'memory' (b)' key'fielding' (c)' dynamic'reallocation' (d)' hashing' ' 40.'Four'necessary'conditions'for'deadlock'to'exist'are:'mutual'exclusion,'noG preemption,'circular'wait'and' (a)' hold'and'wait' (b)' deadlock'avoidance' (c)' race'around'condition' (d)' buffer'overflow' ' 41.'If'you'do'not'know'which'version'of'MSGDOS'you'are'working'with,'which'command' will'you'use'after'having'booted'your'operating'system?' '


(a)' FORMAT'command' (c)' VER'command'

'


(b)' DIR'command' (d)' DISK'command'

' 42.'The'errors'that'can'be'pointed'out'by'the'compiler'are' (a)' Syntax'errors' (b)' Semantic'errors' (c)' Logical'errors' (d)' Internal'errors' ' 43.'When'a'computer'is'first'turned'on'or'restarted,'a'special'type'of'absolute'loader'is' executed,'called'a' (a)' "Compile'and'Go"'loader' (b)' Boot'loader' (c)' Bootstrap'loader' (d)' Relating'loader' ' 44.'Which,'of'the'following'checks,'cannot'be'carried'out'on'the'input'data'to'a'system?' (a)' Consistency'check' (b)' Syntax'check' (c)' Range'check' (d)' All'of'the'above' ' 45.'Which'of'the'following'is'characteristic'of'an'operating'system?' (a)' resource'management' (b)' error'recovery' (c)' memory'management' (d)' All'of'the'above' ' ' 46.'The'state'transition'initiated'by'the'user'process'itself'in'an'operating'system'is' (a)' block' (b)' dispatch' (c)' wake'up' (d)' timer'run'out' ' 47.'What'is'the'name'of'the'operating'system'which'was'originally'designed'by' scientists'and'engineers'for'use'by'scientists'and'engineers?' (a)' XENIX' (b)' UNIX' (c)' OS/2' (d)' MS'DOS' ' 48.'In'a'magnetic'disk,'data'is'recorded'in'a'set'of'concentric'tracks'which'are' subdivided'into' (a)' periods' (b)' sectors' (c)' zones' (d)' groups' ' 49.'Which'of'the'following'filename'extension'suggests'that'the'file'is'a'backup'copy'of' another'file?' (a)' TXT' (b)' COM' (c)' BAS' (d)' BAK' ' '


'


50.'A'hardware'device'that'is'capable'of'executing'a'sequence'of'instructions,'is'known' as' (a)' CPU' (b)' ALU' (c)' CU' (d)' Processor' ' 51.'The'Operating'system'manages' (a)' Memory' (b)' Processor' (c)' Disks'and'I/O'devices' (d)' All'of'the'above' ' 52.'The'principles'of'structured'programming'forbid'the'use'of' (a)' WHILEGDO' (b)' GOTO' (c)' IFGTHENGELSE' (d)' DOGWHILE' ' RDBMS! ! 53.'An'oval'represents'which'of'the'following'in'an'EER?' (a)' Attribute' (b)' Entity' (c)' Optional'One' (d)' Relationship' ' 54.'A'rectangle'represents'which'of'the'following'in'an'EER?' (a)' Attribute' (b)' Entity' (c)' Optional'One' (d)' Relationship' ' 55.'Which'of'the'following'indicates'the'maximum'number'of'entities'that'can'be' involved'in'a'relationship?' (a)' Minimum'cardinality' (b)' Maximum'cardinality' (c)' ERD' (d)' Greater'Entity'Count'(GEC)' ' 56.'In'a'oneGtoGmany'relationship,'the'entity'that'is'on'the'one'side'of'the'relationship'is' called'a(n)'________'entity.' (a)' Parent' (b)' Child' (c)' Instance' (d)' Subtype' 57.'A'recursive'relationship'is'a'relationship'between'an'entity'and'________'.' (a)' itself' (b)' subtype'entity' (c)' archetype'entity' (d)' instance'entity' ' 58.'Which'of'the'following'refers'to'something'that'can'be'identified'in'the'users''work' environment,'something'that'the'users'want'to'track?' (a)' Entity' (b)' Attribute' (c)' Identifier' (d)' Relationship' '


'


' 59.'In'which'of'the'following'is'a'singleGentity'instance'of'one'type'related'to'many' entity'instances'of'another'type?' (a)' OneGtoGOne'Relationship' (b)' OneGtoGMany'Relationship' (c)' ManyGtoGMany'Relationship' (d)' Composite'Relationship' ' 60.'Which'type'of'entity'has'its'relationship'to'another'entity'determined'by'an' attribute'in'that'other'entity'called'a'discriminator?' (a)' Super'type'entity' (b)' Subtype'entity' (c)' Archetype'entity' (d)' Instance'entity' ' 61.'Every'time'attribute'A'appears,'it'is'matched'with'the'same'value'of'attribute'B,'but' not'the'same'value'of'attribute'C.'Therefore,'it'is'true'that:' (a)' A'→'B.' (b)' A'→'C.' (c)' A'→'(B,C).' (d)' (B,C)'→'A' ' 62.'A'relation'is'in'this'form'if'it'is'in'BCNF'and'has'no'multivalued'dependencies:' (a)' second'normal'form' (b)' third'normal'form' (c)' fourth'normal'form' (d)' domain/key'normal'form' ' 63.'Row'is'synonymous'with'the'term:' (a)' Record' (b)' Relation' (c)' Column' (d)' Field' ' 64.'The'primary'key'is'selected'from'the:' (a)' composite'keys' (b)' determinants' (c)' candidate'keys' (d)' foreign'keys' ' 65.'Which'of'the'following'is'a'group'of'one'or'more'attributes'that'uniquely'identifies'a' row?' (a)' Key' (b)' Determinant' (c)' Tuple' (d)' Relation' ' 66.'A'relation'is'considered'a:' (a)' Column' (b)' oneGdimensional'table' (c)' twoGdimensional'table' (d)' threeGdimensional'table' ' 67.'A'functional'dependency'is'a'relationship'between'or'among:' (a)' Tables' (b)' Rows' (c)' Relations' (d)' Attributes' '


'


' 68.'An'attribute'is'a(n):' (a)' column'of'a'table' (b)' two'dimensional'table' (c)' row'of'a'table' (d)' key'of'a'table' ' 69.'A'tuple'is'a(n):' (a)' column'of'a'table' (b)' two'dimensional'table' (c)' row'of'a'table' (d)' key'of'a'table' ' 70.'Eliminating'modification'anomalies'is'a(n)'________'of'normalization.' (a)' advantage' (b)' disadvantage' (c)' Ambiguity' (d)' Disambiguaty' ' 71.'When'assessing'the'table'structure'of'an'acquired'set'of'tables'with'data,' determining'foreign'keys'is'(part'of)'the:' (a)' first'step' (b)' second'step' (c)' third'step' (d)' fourth'step' ' 72.'Most'of'the'time,'modification'anomalies'are'serious'enough'that'tables'should'be' normalized'into:' (a)' 1NF' (b)' 2NF' (c)' 3NF' (d)' BCNF' ' 73.'Normalization'________'data'duplication.' (a)' Eliminates' (b)' Reduces' (c)' Increases' (d)' Maximizes' ' Query!languages!(SQL)! ' 74.'The'SQL'command'to'create'a'table'is:' (a)' MAKE'TABLE' (b)' ALTER'TABLE' (c)' DEFINE'TABLE' (d)' CREATE'TABLE' ' 75.'The'SQL'statement'to'create'a'view'is:' (a)' CREATE'VIEW.' (b)' MAKE'VIEW.' (c)' SELECT'VIEW.' (d)' INSERT'VIEW.' ' 76.'To'update'an'SQL'view,'the'DBMS'must'be'able'to'associate'the'column(s)'to'be' updated'with:' (a)' a'particular'column'in'a'particular' (b)' a'particular'column'in'a'particular' '


underlying'table' (c)' a'particular'row'in'a'particular' underlying'table'

'


row' (d)' None'of'the'above'is'correct'

' 77.'Which'of'the'following'is'NOT'a'type'of'SQL'constraint?' (a)' PRIMARY'KEY' (b)' FOREIGN'KEY' (c)' ALTERNATE'KEY' (d)' UNIQUE' ' 78.'What'is'an'SQL'virtual'table'that'is'constructed'from'other'tables?' (a)' Just'another'table' (b)' A'view' (c)' A'relation' (d)' Query'results' ' 79.'When'using'the'SQL'INSERT'statement:' (a)' rows'can'be'modified'according' (b)' rows'cannot'be'copied'in'mass'from' to'criteria'only' one'table'to'another'only' (c)' rows'can'be'inserted'into'a'table' (d)' rows'can'either'be'inserted'into'a' only'one'at'a'time'only' table'one'at'a'time'or'in'groups' ' 80.'Which'of'the'following'is'an'SQL'trigger'supported'by'Oracle?' (a)' BEFORE' (b)' INSTEAD'OF' (c)' AFTER' (d)' All'of'the'above.' ' 81.'The'SQL'ALTER'statement'can'be'used'to:' (a)' change'the'table'structure.' (b)' change'the'table'data.' (c)' add'rows'to'the'table.' (d)' delete'rows'from'the'table.' ' 82.'What'SQL'structure'is'used'to'limit'column'values'of'a'table?' (a)' LIMIT'constraint' (b)' CHECK'constraint' (c)' VALUE'constraint' (d)' None'of'the'above' ' 83.'Views'constructed'from'SQL'SELECT'statements'that'conform'to'the'SQLG92' standard'may'not'contain:' (a)' GROUP'BY' (b)' WHERE' (c)' ORDER'BY' (d)' FROM' ' 84.'Which'is'NOT'one'of'the'most'common'types'of'SQL'CHECK'constraints?' (a)' System'date' (b)' Range'checks' (c)' Lists'of'values' (d)' Comparing'columns'within'table' ' 85.'The'SQL'WHERE'clause:' '


(a)' limits'the'column'data'that'are' returned' (c)' Both'A'and'B'are'correct'

'


(b)' limits'the'row'data'are'returned' (d)' Neither'A'nor'B'are'correct'

' 86.'The'command'to'eliminate'a'table'from'a'database'is:' (a)' REMOVE'TABLE'CUSTOMER;' (b)' DROP'TABLE'CUSTOMER;' (c)' DELETE'TABLE'CUSTOMER;' (d)' UPDATE'TABLE'CUSTOMER;' ' 87.'ON'UPDATE'CASCADE'ensures'which'of'the'following?' (a)' Normalization' (b)' Data'Integrity' (c)' Materialized'Views' (d)' All'of'the'above' ' 88.'SQL'data'definition'commands'make'up'a(n)'________'.' (a)' DDL' (b)' DML' (c)' HTML' (d)' XML' ' 89.'Which'of'the'following'is'valid'SQL'for'an'Index?' (a)' CREATE'INDEX'ID;' (b)' CHANGE'INDEX'ID;' (c)' ADD'INDEX'ID;' (d)' REMOVE'INDEX'ID;' ' 90.'The'SQL'keyword(s)'________'is'used'with'wildcards.' (a)' LIKE'only' (b)' IN'only' (c)' NOT'IN'only' (d)' IN'and'NOT'IN' ' 91.'Which'of'the'following'is'the'correct'order'of'keywords'for'SQL'SELECT'statements?' (a)' SELECT,'FROM,'WHERE' (b)' FROM,'WHERE,'SELECT' (c)' WHERE,'FROM,SELECT' (d)' SELECT,WHERE,FROM' ' 92.'Which'of'the'following'are'the'five'builtGin'functions'provided'by'SQL?' (a)' COUNT,'SUM,'AVG,'MAX,'MIN' (b)' SUM,'AVG,'MIN,'MAX,'MULT' (c)' SUM,'AVG,'MULT,'DIV,'MIN' (d)' SUM,'AVG,'MIN,'MAX,'NAME' ' ' ' ' 93.'To'remove'duplicate'rows'from'the'results'of'an'SQL'SELECT'statement,'the' ________'qualifier'specified'must'be'included.' (a)' ONLY' (b)' UNIQUE' (c)' DISTINCT' (d)' SINGLE' ' '


'


94.'Which'one'of'the'following'sorts'rows'in'SQL?' (a)' SORT'BY' (b)' ALIGN'BY' (c)' ORDER'BY' (d)' GROUP'BY' ' 95.'The'SQL'statement'that'queries'or'reads'data'from'a'table'is'________'.' (a)' SELECT' (b)' READ' (c)' QUERY' (d)' None'of'the'above'is'correct' ' 96.'________'was'adopted'as'a'national'standard'by'ANSI'in'1992.' (a)' Oracle' (b)' SQL' (c)' Microsoft'Access' (d)' Dbase' ' 97.'SQL'is:' (a)' a'programming'language' (b)' a'data'sublanguage' (c)' an'operating'system' (d)' a'DBMS' ' File!structures! ' 98.'Consider'a'B+Gtree'in'which'the'maximum'number'of'keys'in'a'node'is'5.'What'is'the' minimum'number'of'keys'in'any'nonGroot'node?' (a)' 1' (b)' 2' (c)' 3' (d)' 4' ' 99.'A'clustering'index'is'defined'on'the'fields'which'are'of'type' (a)' nonGkey'and'ordering' (b)' nonGkey'and'nonGordering' (c)' key'and'ordering' (d)' key'and'nonGordering' ' 100.'Mapping'of'file'is'managed'by' (a)' file'metadata' (b)' page'table' (c)' virtual'memory' (d)' file'system' ' '101.'In'which'of'the'following'file'organization,'sequential'file'processing'is'impractical?' (a)' Indexed'sequential' (b)' Indexed' (c)' BGtree' (d)' Hashed' ' 102.'Each'node'of'a'B+'tree'contain'a'____'and'the'search'key'value?' (a)' Pointer' (b)' Chain' (c)' Address' (d)' None'of'the'above' ' 103.'What'does'‘B’'in'BGtree'means?' '


(a)' Better' (c)' Balanced'

'


(b)' Binary' (d)' Byte'

' ' ' 104.'Which'of'the'following'hashing'technique'that'involve'applying'an'arithmetic' function'or'logical'function'to'different'portion'of'hash'field'value'to'calculate'the'hash' address?' (a)' Mod'hashing' (b)' Open'hashing' (c)' Multiple'hashing' (d)' Folding' ' 105.'Bitmaps'can'be'used'as'a'compressed'storage'mechanism'at'the'leaf'nodes'of' ________'for'those'values'that'occur'very'frequently.' (a)' BGtrees' (b)' B+Gtrees' (c)' Bit'trees' (d)' Both'a'and'b' ' 106.'In'a'B+Gtree'index'______,'for'each'value'we'would'normally'maintain'a'list'of'all' records'with'that'value'for'the'indexed'attribute.' (a)' Leaf' (b)' Node' (c)' Root' (d)' Link' ' 107.'In'ordered'indices'the'file'containing'the'records'is'sequentially'ordered,'a' ___________'is'an'index'whose'search'key'also'defines'the'sequential'order'of'the'file.' (a)' Clustered'index' (b)' Structured'index' (c)' Unstructured'index' (d)' Nonclustered'index' ' 108.'The'method'of'access'that'uses'key'transformation'is'called'as' (a)' Direct' (b)' Hash' (c)' Random' (d)' Sequential' ' 109.'Why'do'we'need'concurrency'control'on'B+'trees'?' (a)' To'remove'the'unwanted'data' (b)' To'easily'add'the'index'elements' (c)' To'maintain'accuracy'of'index' (d)' All'of'the'mentioned' ' 110.'How'many'techniques'are'available'to'control'concurrency'on'B+'trees?' (a)' One' (b)' Three' (c)' Four' (d)' None'of'the'above' ' 111.'In'crabbing'protocol'the'the'lock'obtained'on'the'root'node'is'in'_________'mode.' (a)' Shared' (b)' Exclusive' '


(c)' Read'only'

'


(d)' None'of'the'above'

' 112.'BGlink'tree'requires'a'pointer'to'its'__________'sibling.' (a)' Upper' (b)' Lower' (c)' Right' (d)' Left' ' 113.'Instead'of'locking'index'leaf'nodes'in'a'twoGphase'manner,'some'index' concurrencyGcontrol'schemes'use'___________'on'individual'key'values,'allowing'other' key'values'to'be'inserted'or'deleted'from'the'same'leaf.' (a)' B+'tree'locking' (b)' Link'level'locking' (c)' KeyGvalue'locking' (d)' Next'value'locking' ' 114.'A'_________'consists'of'a'sequence'of'query'and/or'update'statements.' (a)' Transaction' (b)' Commit' (c)' Rollback' (d)' Flashback' ' ' ' ' 115.'Which'of'the'following'is'a'property'of'transactions?' (a)' Atomicity' (b)' Concurrency' (c)' Isolation' (d)' All'of'the'above' ' 116.'Isolation'of'the'transactions'is'ensured'by' (a)' Transaction'management' (b)' Application'programmer' (c)' Concurrency'control' (d)' Recovery'management' ' 117.'Problems'occurs'if'we'don’t'implement'proper'locking'strategy' (a)' Dirty'reads' (b)' Phantom'reads' (c)' Lost'updates' (d)' Unrepeatable'reads' ' Programming!in!C! ' 118.'Which'of'the'following'special'symbol'allowed'in'a'variable'name?' (a)' *'(asterisk)' (b)' |'(pipeline)' (c)' (hyphen)' ' (d)' _'(underscore)' ' 119.'By'default'a'real'number'is'treated'as'a' (a)' float' (b)' double' (c)' long'double' (d)' far'double' '


'


' 120.'Is'the'following'statement'a'declaration'or'definition?' (a)' extern'int'i;' (b)' Declaration' (c)' Definition' (d)' Function' ' 121.'Identify'which'of'the'following'are'declarations' 1':' extern'int'x;' 2':' float'square'('float'x')'{'...'}' 3':' double'pow(double,'double);' (a)' 1''and'2' (b)' 2'and'3' (c)' 1'and'3' (d)' 3' ' 122.'When'we'mention'the'prototype'of'a'function?'We'are_____.' (a)' Defining' (b)' Declaring' (c)' Prototyping' (d)' Calling' ' 123.'Which'of'the'following'declaration'is'correct?' (a)' int'length;' (b)' char'int;' (c)' int'long;' (d)' float'double;' ' 124.'Which'of'the'following'operations'are'INCORRECT?' (a)' int'i'='35;'i'='i%5;' (b)' short'int'j'='255;'j'='j;' (c)' long'int'k'='365L;'k'='k;' (d)' float'a'='3.14;'a'='a%3;' ' 125.'Which'of'the'following'correctly'represents'a'long'double'constant?' (a)' 6.68' (b)' 6.68L' (c)' 6.68LF' (d)' 6.68f' ' ' ' 126.'Which'of'the'following'is'not'logical'operator?' (a)' &' (b)' &&' (c)' ||' (d)' !' ' 127.'In'mathematics'and'computer'programming,'which'is'the'correct'order'of' mathematical'operators'?' (a)' Addition,'Subtraction,' (b)' Division,'Multiplication,'Addition,' Multiplication,'Division' Subtraction' (c)' Multiplication,'Addition,'Division,' (d)' Addition,'Division,'Modulus,' Subtraction' Subtraction' '


'


' 128.'Which'of'the'following'cannot'be'checked'in'a'switchGcase'statement?' (a)' Character' (b)' Integer' (c)' Float' (d)' Enum' ' 129.'Which'of'the'following'is'the'correct'usage'of'conditional'operators'used'in'C?' (a)' a>b'?'c=30':'c=40;' (b)' a>b'?'c=30;' (c)' max'='a>b'?'a>c?a:c:b>c?b:c' (d)' return'(a>b)?(a:b)' ' 130.'Which'of'the'following'is'the'correct'order'if'calling'functions'in'the'below'code?' a'='f1(23,'14)'*'f2(12/4)'+'f3();' (a)' f1,'f2,'f3' (b)' f3,'f2,'f1' (c)' Order'may'vary'from'compiler'to' (d)' None'of'above' compiler' ' 131.'Assuming,'integer'is'2'byte,'What'will'be'the'output'of'the'program?' !!!!!!!#include' ' '''''''int'main()' '''{' ''''''printf("%x\n",'G2<<2);' '''''return'0;' ''}' (a)' ffff' (b)' 0' (c)' error' (d)' Fff8' ! 132.'The'binary'equivalent'of'5.375'is' (a)' 101.101110111' (b)' 101.011' (c)' 101011' (d)' None'of'above' ' 133.'The'keyword'used'to'transfer'control'from'a'function'back'to'the'calling'function'is' (a)' switch' (b)' goto' (c)' go'back' (d)' return' ' 134.'What'is'(void*)0?' (a)' Representation'of'NULL'pointer' (b)' Representation'of'void'pointer' (c)' Error' (d)' None'of'above' ' 135.'In'which'header'file'is'the'NULL'macro'defined?' (a)' stdio.h' (b)' stddef.h' '


(c)' stdio.h'and'stddef.h'

'


(d)' math.h'

' ' ' 136.'The'operator'used'to'get'value'at'address'stored'in'a'pointer'variable'is' (a)' *' (b)' &' (c)' &&' (d)' ||' ' 137.'In'C,'if'you'pass'an'array'as'an'argument'to'a'function,'what'actually'gets'passed?' (a)' Value'of'elements'in'array' (b)' First'element'of'the'array' (c)' Base'address'of'the'array' (d)' Address'of'the'last'element'of'array' ' 138.'Which'of'the'following'function'sets'first'n'characters'of'a'string'to'a'given' character?' (a)' strinit()' (b)' strnset()' (c)' strset()' (d)' strcset()' ' 139.'If'the'two'strings'are'identical,'then'strcmp()'function'returns' (a)' G1' (b)' 1' (c)' 0' (d)' Yes' ' 140.'How'will'you'print'\n'on'the'screen?' (a)' printf("\n");' (b)' echo'"\\n";' (c)' printf('\n');' (d)' printf("\\n");' ' 141.'Which'of'the'following'function'is'used'to'find'the'first'occurrence'of'a'given'string' in'another'string?' (a)' strchr()' (b)' strrchr()' (c)' strstr()' (d)' strnset()' ' 142.'Which'of'the'following'function'is'more'appropriate'for'reading'in'a'multiGword' string?' (a)' printf();' (b)' scanf();' (c)' gets();' (d)' puts();' ' 143.'In'which'numbering'system'can'the'binary'number'1011011111000101'be'easily' converted'to?' (a)' Decimal'system' (b)' Hexadecimal'system' (c)' Octal'system' (d)' No'need'to'convert' ' '


'


144.'Which'bitwise'operator'is'suitable'for'turning'on'a'particular'bit'in'a'number?' (a)' &&'operator' (b)' &'operator' (c)' ||'operator' (d)' |'operator' ' Object!Oriented!Programming! ' 145.'Procedure'oriented'Programs'are'called'as' (a)' Structured'programming' (b)' Object'oriented'programming' (c)' Functional'programming' (d)' None'of'the'above' 146.'A'_____________'is'a'class'whose'instances'themselves'are'classes.' (a)' subclass' (b)' abstarct'class' (c)' metaclass' (d)' object'class' ' 147.'_______________'enables'you'to'hide,'inside'the'object,'both'the'data'fields'and' the'methods'that'act'on'that'data.' (a)' Encapsulation' (b)' Polymorphism' (c)' Inheritance' (d)' Overloading' ' ' 148.'For'a'16'bit'word'length'Integer'data'type'values'lie'between'________________' (a)' –32768'to'32767.' (b)' 0'to'32767' (c)' G128'to'128' (d)' 0'to'128' ' 149.'Which'of'the'following'is'NOT'a'Relational'Operator' (a)' ==' (b)' >' (c)' %' (d)' !=' ' 150.'A'__________'is'an'abstract'idea'that'can'be'represented'with'data'structures'and' functions.' (a)' class' (b)' object' (c)' loop' (d)' data'type' ' 151.'Automatic'Initialization'of'object'is'carried'out'using'a'special'member'function' called'____________________' (a)' friend' (b)' casting' (c)' reference'parameter' (d)' constructor' ' 152.'A'class'can'allow'nonGmember'functions'and'other'classes'to'access'its'own'private' data,'by'making'them'as'_________________.' (a)' private' (b)' protected' '


(c)' Friend'

'


(d)' Public'

' 153.'____________________'is'the'process'of'creating'new'classes,'called'derived' classes,'from'existing'classes'called'base'class' (a)' Inheritance' (b)' encapsulation' (c)' Polymorphism' (d)' Overloading' ' 154.'A'___________'class'can'share'selected'properties'of'its'base'classes,' (a)' abstarct' (b)' derived' (c)' subclass' (d)' both'b'&'c' ' 155.'A'_______________'is'the'address'of'a'memory'location'and'provides'an'indirect' way'of'accessing'data'in'memory.' (a)' Constant' (b)' variable' (c)' Pointer' (d)' Object' ' 156.'To'perform'identical'operations'for'each'type'of'data'compactly'and'conveniently' we'have'to'use' (a)' Exception' (b)' constant'parameter' (c)' function'templates' (d)' None'of'the'above' ' 157.'In'graphics'mode'the'basic'element'is'a'__________' (a)' character' (b)' text' (c)' table' (d)' pixel' ' 158.'The'________________'objects'have'values'that'can'be'tested'for'various'error' conditions.' (a)' osstream' (b)' ofstream' (c)' stream' (d)' ifstream' ' 159.'Which'function'return'the'current'position'of'the'get'or'put'pointer'in'bytes.' (a)' tellg'()' (b)' tellp'()' (c)' tell'()' (d)' Both'A'and'B' ' 160.'________________'is'a'technique'that'allows'the'user'considerable'flexibility'in' the'way'the'programs'are'used' (a)' Redirection' (b)' manipulation' (c)' Detecting' (d)' None'of'the'above' ' 161.'The'advantages'of'OOP'are','' '


'


1.'increased'programming'productivity'' 2.'decreased'maintenance'costs.' 3.'less'time'to'execute'' 4.'easy'to'understand' (a)' 1&'3' (b)' 1&'2' (c)' 3&'4' (d)' 2&'3' ' 162.'To'overload'an'operator'_____________keyword'must'be'used'along'with'the' operator'to'be'overloaded.' (a)' Over' (b)' Overload' (c)' void' (d)' Operator' ' 163.'In'the'below'Declaration'how'many'copies'of'x'does'DC'inherits'?'' Class'BC'{'Private:'int'x;'};'Class'BC1:'virtual'public'BC'{'Private':'Float'y;'};'Class'BC2:' virtual'public'BC'{Private:'float'z;'};'Class'DC:'public'BC1,'Public'Bc2'{'};' (a)' One' (b)' Two' (c)' Zero' (d)' Syntax'error' ' ' ! !

'


'


Answers:!Information!Technology!MCQS! 1.!!(a)!

2.!(b)!

3.!(b)!

4.!(a)!

5.!(a)!

6.!(c)!

7.!(d)!

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Radar Theory Contents 1 Introduction

2

2 Radar Fundamentals

2

3 Basic Radar Concept

3

4 Radar Component 4.1 Synchronizer (Timer) . 4.2 Transmitter . . . . . . 4.3 Duplexer . . . . . . . . 4.4 Antenna System . . . 4.5 Receiver . . . . . . . . 4.6 Indicator . . . . . . . .

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3 4 4 5 5 5 6

5 Radar transmission methods 5.1 Continuous wave method: Doppler Effect 5.1.1 Doppler effect . . . . . . . . . . . . 5.1.2 Doppler frequency Shift . . . . . . 5.2 Frequency-modulation Method . . . . . . 5.3 Pulse Modulation Method . . . . . . . . .

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6 Radar Range Equation

7

7 Moving target indication

8

8 Pulse-Doppler radar 8.1 Range measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Pulse repetition frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 9 9

9 Tracking Radar

9

1

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Introduction • RADAR (Radio Detection and Ranging) is a system used mainly in defense applications which is used to locate the target, that is, to find its exact position in the range which it covers. • The drawback of conventional pulse RADAR is that it can determine only the range, that is, the distance of the target from RADAR antenna. It cannot determine whether the target is moving or not and in which direction it is moving. • Thus in order to determine the motion of the target we use MTI (Moving Target Indication) RADAR. • MTI RADAR has become a boon for detecting motion of the targets in the field of RADAR Engineering. • MTI RADAR is defined as the RADAR in which the Doppler effect can be employed to differentiate between stationary and moving targets, with the former suppressed and only the latter displayed. In this process, the permanent echoes as well as those from very slow moving objects (if desired) are not displayed on the PPI (plan position indicator), and the radar controller can pay attention to the real aircraft. • Along with the detection of moving targets it also eliminates the effect of stationary objects or stationary clutters. This can be achieved by using the Delay line cancellor

2

Radar Fundamentals

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• The term RADAR is common in today’s everyday language. You probably use it yourself when referring to a method of recording the speed of a moving object. • The term Radar is an acronym made up of the words radio detection and ranging.

• The term is used to refer to electronic equipment that detect the presence, direction, height, and distance of objects by using reflected electromagnetic energy. • Electromagnetic energy of the frequency used for radar is unaffected by darkness and also penetrates weather to some degree, depending on frequency. It permits radar systems to determine the positions of ships, planes, and land masses that are invisible to the naked eye because of distance, darkness, or weather. . • World War II provided a strong incentive to develop practical radar, and early versions were in use soon after the war began. Radar technology has improved in the years since the war. We now have radar systems that are smaller, more efficient, and better than those early versions. • Modern radar systems are used for early detection of surface or air objects and provide extremely accurate information on distance, direction, height, and speed of the objects. Radar is also used to guide missiles to targets and direct the firing of gun systems. Other types of radar provide long-distance surveillance and navigation information.


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Basic Radar Concept

• The electronics principle on which radar operates is very similar to the principle of soundwave reflection.

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• If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. • The time required for a return echo can be roughly converted to distance if the speed of sound is known. • Radar uses electromagnetic energy pulses in much the same way, as shown in the above figure . • The radio-frequency (rf) energy is transmitted to and reflects from the reflecting object. A small portion of the energy is reflected and returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object.

4

Radar Component

Pulse radar systems can be functionally divided into the six essential components shown in below given figure. These components are briefly described in the following paragraphs and will be


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explained in detail after that: 1. The SYNCHRONIZER (also referred to as the TIMER or KEYER) supplies the synchronizing signals that time the transmitted pulses, the indicator, and other associated circuits. 2. The TRANSMITTER generates electromagnetic energy in the form of short, powerful pulses.

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3. The DUPLEXER allows the same antenna to be used for transmitting and receiving. 4. The ANTENNA SYSTEM routes the electromagnetic energy from the transmitter, radiates it in a highly directional beam, receives any returning echoes, and routes those echoes to the receiver. 5. The RECEIVER amplifies the weak, electromagnetic pulses returned from the reflecting object and reproduces them as video pulses that are sent to the indicator.

4.1

Synchronizer (Timer)

The synchronizer ensures that all circuits connected with the radar system operate in a definite timed relationship. It also times the interval between transmitted pulses to ensure that the interval is of the proper length. Timing pulses are used to ensure synchronous circuit operation and are related to the prf. The prf can be set by any stable oscillator, such as a sine-wave oscillator, multivibrator, or a blocking oscillator. That output is then applied to pulse-shaping circuits to produce timing pulses. Associated components can be timed by the output of the synchronizer or by a timing signal from the transmitter as it

4.2

Transmitter

The transmitter generates powerful pulses of electromagnetic energy at precise intervals. The required power is obtained by using a high-power microwave oscillator, such as a Engineering Knowledge Test

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magnetron, or a microwave amplifier, such as a klystron, that is supplied by a low-power rf source. The high-power generator, whether an oscillator or amplifier, requires operating power in the form of a properly-timed, high-amplitude, rectangular pulse. This pulse is supplied by a transmitter unit called the MODULATOR. When a high-power oscillator is used, the modulator high-voltage pulse switches the oscillator on and off to supply high-power electromagnetic energy. When a microwave power amplifier is used, the modulator pulse activates the amplifier just before the arrival of an electromagnetic pulse from a preceding stage or a frequency-generation source. Normally, because of the extremely high voltage involved, the modulator pulse is supplied to the cathode of the power tube and the plate is at ground potential to shield personnel from shock hazards. The modulator pulse may be more than 100,000 volts in high-power radar transmitters. In any case, radar transmitters produce voltages, currents, and radiation hazards that are extremely dangerous to personnel. Safety precautions must always be strictly observed when working in or around a radar transmitter

4.3

Duplexer

A duplexer is essentially an electronic switch that permits a radar system to use a single antenna to both transmit and receive. The duplexer must connect the antenna to the transmitter and disconnect the antenna from the receiver for the duration of the transmitted pulse. The receiver must be completely isolated from the transmitted pulse to avoid damage to the extremely sensitive receiver input circuitry. After the transmitter pulse has ended, the duplexer must rapidly disconnect the transmitter and connect the receiver to the antenna. The switching time is called receiver recovery time, and must be very fast if close-in targets are to be detected. Additionally, the duplexer should absorb very little power during either phase of operation. Low-loss characteristics are particularly important during the receive period of duplexer operation. This is because the received signals are of extremely low amplitude.

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4.4

Antenna System

The antenna system routes the pulse from the transmitter, radiates it in a directional beam, picks up the returning echo, and passes it to the receiver with a minimum of loss. The antenna system includes the antenna, transmission lines and waveguide from the transmitter to the antenna, and the transmission line and waveguide from the antenna to the receiver. In some publications the duplexer is included as a component of the antenna system.

4.5

Receiver

The receiver accepts the weak echo signals from the antenna system, amplifies them, detects the pulse envelope, amplifies the pulses, and then routes them to the indicator. One of the primary functions of the radar receiver is to convert the frequency of the received echo signal to a lower frequency that is easier to amplify. This is because radar frequencies are very high and difficult to amplify. This lower frequency is called the INTERMEDIATE FREQUENCY (IF). The type of receiver that uses this frequency conversion technique is the SUPER HETERODYNE RECEIVER. Superheterodyne receivers used in radar systems must


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have good stability and extreme sensitivity. Stability is ensured by careful design and the overall sensitivity is greatly increased by the use of many IF stages

4.6

Indicator

The indicator uses the received signals routed from the radar receiver to produce a visual indication of target information. The cathode-ray oscilloscope is an ideal instrument for the presentation of radar data. This is because it not only shows a variation of a single quantity, such as voltage, but also gives an indication of the relative values of two or more quantities. The sweep frequency of the radar indicator is determined by the pulse-repetition frequency of the radar system. Sweep duration is determined by the setting of the range-selector switch. Since the indicator is so similar to an oscilloscope, the term RADAR SCOPE is commonly used when referring to radar indicators.

5

Radar transmission methods

5.1

Continuous wave method: Doppler Effect

When radio-frequency energy transmitted from a fixed point continuously strikes an object that is either moving toward or away from the source of the energy, the frequency of the reflected energy is changed. This shift in frequency is known as the DOPPLER EFFECT. The difference in frequency between the transmitted and reflected energy indicates both the presence and the speed of a moving target. 5.1.1

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Doppler effect

A common example of the Doppler effect in action is the changing pitch of the whistle of an approaching train. The whistle appears to change pitch from a high tone, as the train approaches, to a lower tone as it moves away from the observer. As the train approaches, an apparent increase in frequency (an increase in pitch) is heard; as the train moves away, an apparent decrease in frequency (a decrease in pitch) is heard. This pitch variation is known as the Doppler effect. 5.1.2

Doppler frequency Shift

• Doppler shift is an apparent change in frequency (or wavelength) due to the relative motion of two objects. Either one or both of the objects may be moving with respect to the ground. • Radar systems exploit the Doppler shift to provide an indication of relative speed.

• When the two objects are approaching each other (closing), the Doppler shift causes a shortening of wavelength - or increase infrequency. • When the two objects are receding from each other (opening), the Doppler shift causes a lengthening of wavelength - or decrease in frequency. • In case of an MTI RADAR, when the target is moving towards the RADAR, the frequency of the echo received from the target increases whereas if the target is moving away from the RADAR, the frequency of the echo received from the target decreases. Engineering Knowledge Test

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• Difference in the transmitted frequency and received frequency from the target is called as dopplar frequency and is denoted by fd.

5.2

Frequency-modulation Method

In the frequency-modulation method, the transmitter radiates radio-frequency waves. The frequency of these rf waves is continually increasing and decreasing from a fixed reference frequency. At any instant, the frequency of the returned signal differs from the frequency of the radiated signal. The amount of the difference frequency is determined by the time it took the signal to travel the distance from the transmitter to the object.

5.3

Pulse Modulation Method

In this method the radio-frequency energy can also be transmitted in very short bursts, called pulses. These pulses are of extremely short time duration, usually on the order of 0.1 microsecond to approximately 50 microseconds. In this method, the transmitter is turned on for a very short time and the pulse of radiofrequency energy is transmitted.

6

Radar Range Equation • The radar range equation is commonly used to estimate radar system performance, given that line-of-sight conditions are satisfied.

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• This formulation essentially computes the signal-to-noise ratio (S/N) at the output of the radar signal processor. • In turn, S/N is used to provide estimates of radar detection and position measurement performance as described in subsequent subsections. S/N can be calculated in terms of the number of pulses coherently integrated over a single coherent processing interval (CPI) using the radar range equation such that: S/N =

P GATp Np ‡ (4fi)2 R4 Lt Lrn Lsp kts

– where P is peak transmitter power output, – G is directivity of the transmit antenna, – A is effective aperture area of the receive antenna in meters squared, – Tp is pulse duration, s is radar cross-section in square meters, – Np is the number of coherently integrated pulses within the coherent processing interval, R is range to target in meters, – Lt is system ohmic and nonohmic transmit losses, – Lm is system nonohmic receive losses, – Lsp is signal processing losses, – k is Boltzman’s constant (1.38 ◊ 1023 K) and

– Ts is system noise temperature, including receive ohmic losses (Kelvin). S/N losses are derived relative to matched filter performance.


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Moving target indication

The MTI radar uses Low Pulse Repetition Frequency (PRF) to avoid range ambiguities. Moving target indicator signal sampling process. Moving target indicator (MTI) begins with sampling two successive pulses. Sampling begins immediately after the radar transmit pulse ends. The sampling continues until the next transmit pulse begins. • The purpose of moving-target indication (MTI) radar is to reject signals from fixed or slow-moving unwanted targets, such as buildings, hills, trees, sea, and rain, and retain for detection or display signals from moving targets such as aircraft. • MTI radar utilizes the doppler shift imparted on the reflected signal by a moving target to distinguish moving targets from fixed targets. • In a pulse radar system this doppler shift appears as a change of phase of received signals between consecutive radar pulses. • Consider a radar which transmits a pulse of RF energy that is reflected by both a building (fixed target) and an airplane (moving target) approaching the radar. The reflected pulses return to the radar a certain time later. The radar then transmits a second pulse. The reflection from the building occurs in exactly the same amount of time, but the reflection from the moving aircraft occurs in less time because the aircraft has moved closer to the radar in the interval between transmitted pulses. The precise time that it takes the reflected signal to reach the radar is not of fundamental importance. What is significant is whether the time changes between pulses. • The time change, which is of the order of a few nanoseconds for an aircraft target, is determined by comparing the phase of the received signal with the phase of a reference oscillator in the radar. If the target moves between pulses, the phase of the received pulses changes.

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8

Pulse-Doppler radar

A Pulse-Doppler radar is a radar system that determines the range to a target using pulsetiming techniques, and uses the Doppler shift of the returned signal to determine the target object’s velocity. It combines the features of pulse radars and continuous-wave radars, which were formerly separate due to the complexity of the electronics A Doppler Radar:


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8.1

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Range measurement

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Pulse-doppler systems measure the range to objects by measuring the elapsed time between sending a pulse of radio energy and receiving a reflection off the object. Radio waves travel at the speed of light, so the distance to the object is the elapsed time multiplied by the speed of light, divided by two - there and back.

8.2

Pulse repetition frequency

Pulse-Doppler typically uses medium Pulse repetition frequency (PRF) from about 3 kHz to 30 kHz. The range between transmit pulses is 5 km to 50 km. Range and velocity cannot be measured directly using medium PRF, and ambiguity resolution is required to identify true range and speed. Doppler signals are generally above 1 kHz, which is audible, so audio signals from medium-PRF systems can be used for passive target classification.

9

Tracking Radar

Radar that provides continuous positional data on a target is called tracking radar. • Most tracking radar systems used by the military are also fire-control radar; the two names are often used interchangeably. • Fire-control tracking radar systems usually produce a very narrow, circular beam.

• Fire-control tracking radar must be directed to the general location of the desired target because of the narrow-beam pattern. This is called the DESIGNATION phase of equipment operation. Engineering Knowledge Test

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• Once in the general vicinity of the target, the radar system switches to the ACQUISITION phase of operation. During acquisition, the radar system searches a small volume of space in a prearranged pattern until the target is located. When the target is located, the radar system enters the TRACK phase of operation. Using one of several possible scanning techniques, the radar system automatically follows all target motions. The radar system is said to be locked on to the target during the track phase. • The three sequential phases of operation are often referred to as MODES and are common to the target-processing sequence of most firecontrol radars. • Typical fire-control radar characteristics include a very high prf, a very narrow pulse width, and a very narrow beam width. These characteristics, while providing extreme accuracy, limit the range and make initial target detection difficult. item A typical firecontrol radar antenna is shown in figure 1-28. In this example the antenna used to produce a narrow beam is covered by a protective radome. A typical fire-control radar antenna is shown below

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Radar Theory


'

Radar'Theory'MCQs'

Radar%Theory%MCQs%

' 1.'''Radar'gives'targets' (a)' Range' (c)' Velocity'and'range' ' 2.'''Radar'is'a/an'____'device.' (a)' Mechanical' (c)' Pneumatic'device' ' 3.''Radar'is'useful'to'see'objects' (a)' Hidden'behind'conductors' (c)' In'rain'and'fog'

' 4.''High'power'radar'transmitter'uses' (a)' Magnetrons' (c)' MOSFETs' ' 5.''Duplex'isolates' (a)' Transmitter'while'transmitting' (c)' Receiver'while'transmitting' ' 6.''Radar'receiver'contains' (a)' Matched'filters' (c)' No'PPI' ' 7.''CW'radar'can'be' (a)' Monostatic'only' (c)' Static'only' ' 8.''Received'radar'power'is'' (a)' Proportional'to'!' (c)' Inversely'proportional'to'!'' ' 9.''Receiver'power'depends'on' (a)' Medium'losses'

'

(b)' Size' (d)' Color' (b)' Electromagnetic' (d)' Electrical' (b)' Having'different'colors'but'made' of'conductor' (d)' That'are'shielded' (b)' Transistors' (d)' Tunnel'diodes' (b)' Receiver'while'receiving' (d)' Display'unit' (b)' Magnetrons' (d)' No'display'unit' (b)' Monostatic'and'bistatic'' (d)' NonWdoppler' (b)' Proportional'to'!" ' (d)' Inversely'proportional'to'd' (b)' Medium,'transmitter'and'


'

polarization'losses' (d)' Polarization'losses'

(c)' Transmitter'losses' ' 10.''CW'radar'gives' (a)' Range'of'target' (c)' Size'of'target' ' 11.''Pulsed'radar'gives'the'target’s' (a)' Range'and'velocity' (c)' Color' ' 12.''Bistatic'radar' (a)' Has'a'single'antenna'

(b)' Radial'velocity'of'target' (d)' Color'of'target' (b)' Range'only' (d)' Size' (b)' Has'two'antennas'at'the'same' place' (d)' Has'no'antennas'

(c)' Has'two'antennas'at'different' locations' ' 13.'The'transmitter'of'pulsed'radar'has' (a)' Modulator' (c)' Modulator'and'synchronizer' ' 14.''Duplexer'is'called' (a)' switch' (c)' TR'switch' ' 15.''The'receiver'of'pulse'radar'has'' (a)' A'mixer'and'a'local'oscillator' (c)' A'mixer' ' 16.'Match'filter' (a)' Optimizes'SNR' (c)' Filters'RF'signals' ' 17.'Velocity'of'radar'wave'is' (a)' 3$×10( $)*/,' (c)' 300$*/.,'

(b)' No'modulator' (d)' No'synchronizer' (b)' coupler' (d)' amplifier' (b)' A'local'oscillator' (d)' An'AF'amplifier' (b)' Removes'AF'signals' (d)' Is'used'as'amplifier' (b)' 3$×10- )*/,' (d)' 30$*/.,' $

'

Radar'Theory'MCQs'


18.''Doppler'shift'frequency'is'given'by' 234 (a)' /0 $ = $ $/ ' 35 6 (c)' / $ = $ 35 $/ ' 0 34 6 ' 19.'HPRF'pulse'Doppler'radar' (a)' reduces'main'beam'clutter' (c)' increases'range'accuracy' ' 20.'In'modulated'PRF'pulse'radar' (a)' range'resolution'is'poor' (c)' range'resolution'is'better' ' 21.'In'search'radars.' (a)' the'beam'is'scanned' continuously' (c)' angular'position'cannot'be' found' ' 22.'SNR'of'search'radar' (a)' depends'on'starch' (c)' does'not'depend'on'noise' figure'' ' ' ! !

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Radar'Theory'MCQs'

235 $/ ' 34 6 (d)' / $ = $ 34 $/ ' 0 35 6 (b)'

/0 $ = $

(b)' increases'main'beam'clutter' (d)' increases'resolution'of'the'target' (b)' range'accuracy'is'poor' (d)' altitude'returns'are'not' eliminated' (b)' the'beam'is'not'scanned' continuously' (d)' three'antennas'must'be'used.'

(b)' does'not'depend'on'scan'time' (d)' does'not'depend'on'radar'crossW section.'


1.!!(c)!

2.!(b)!

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Radar'Theory'MCQs'

Answers:%Radar%Theory%MCQs% ! ! 3.!(c)! 4.!(a)! 5.!(c)! 6.!(a)! 7.!(b)!

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ELECTRICAL AND ELECTRONICS STREAM ENGINEERING KNOWLEDGE TEST (EKT)

Q1.

If x=a(cos t + t sin t), y=a(sin t – t cos t). The value of (a) cos t (b) sin t (c) tan t

is (d)

sec2 t

Q2.

The area of three faces of a cuboid are in the ratio 2:3:4 and its volume is 9000 cm3. The length of the shortest edge is (a) 15 cm (b) 30 cm (c) 20 cm (d) 60 cm

Q3.

∫

is equal to

(a)

log x+x+c

Q4.

(b)

log(logx)+c

(c)

8/2

(b)

9/20

(c)

Q5.

The projection of a vector on another vector is

Q6.

(a) Scalar (c) neither vector nor scalar In MKS system, we measure

Q8.

+c

(b) (d)

8/15

(d)

2/20

Vector either scalar or vector

(a) mass in kilogram (b) distance in meter (c) time in second (d) all of these When the separation between two charges is made four times, the force between them (a) increases four times (b) decreases four times (c) increases sixteen times (d) decreases sixteen times When a conductor cuts magnetic flux, an emf is induced in the conductor. This is known as (a) (c)

Q9.

(d)

Tickets numbered 1 to 20 are mixed up and then a ticket is drawn at random. What is the probability that the ticket drawn has a number which is a multiple of 3 or 5? (a)

Q7.

xlogx+c

Joule's law Coulomb's law

(b) (d)

Faraday's law Ampere’s law

X-rays are used for the study of crystal structure because (a) X-rays are completely absorbed by the crystal (b) the wavelength of X-ray is of the same order of magnitude in the inter-atomic spacing in crystals (c) the wavelength of X-rays is very small in comparison with the inter-atomic spacing in crystals (d) the crystals are completely transparent to X-rays

Q10. A radioactive isotope has a half-life of 10 days. If today there are 125 g of it left, what was its original weight 40 days earlier (a) 600 g (b) 1000 g (c) 1250 g (d) 2000 g Q11. Angles project true size only when the plane containing the angle and plane of projection are (a) Aligned (b) Adjacent (c) Perpendicular (d) Parallel Q12. Tesla is a measure of (a) magnetic flux density (c) magnetic potential

(b) (d)

electric flux density electric potential

Q13. Admittance is reciprocal of (a) susceptance (b) impedance

(c) reactance

Q14. _________is an active filter (a) RC filter (b) notch filter

(c) Butterworth filter (d)

(d)

conductance band pass filter

Q15. For transmission line load matching over a range of frequencies, it is best to use a (a) Balun (b) broadband directional coupler (c) double stub (d) single stub Q16. Emitter follower is used for (a) reducing the gain (c) impedance matching

(b) (d)

increasing the distortion none of these

Q17. Binary equivalent of (45)10 is (a) (11101)2 (b) (11110)2

(c)

(101101)2

Q18. In Computer memory size K indicates Kilo, which is equal to (a) 1000 (b) 1024 (c) 100

(d)

(110101)2

(d) 10000

Q19. An astable multivibrator has (a) no stable state (b) one stable state (c) three stable states (d) two stable states Q20. An ideal Op Amp has (a) infinite input and output impedance (b) very low input and output impedance (c) low input impedance and very high output impedance (d) infinite input impedance and zero output impedance Q21. An instruction used to set the carry flag in a computer can be classified as a (a) data transfer instruction (b) arithmetic instruction (c) logical instruction (d) program control instruction Q22. An FET is a (a) bipolar semiconductor device (c) non semiconductor device

(b) (d)

unipolar semiconductor device both (a) and (c)

Q23. For Gunn diodes, semiconductor material preferred is (a) Silicon (b) Germanium (c) Gallium Arsenide

(d) all of these

Q24. In a JFET drain current is maximum when VGS is (a) zero

(b)

negative

(c) positive

(d) equal to Vp

Q25. The output of Laser is (a)

Infrared

(b)

polarised

(c)

narrow beam (d)

coherent

Q26. As compared to a closed loop system an open loop system is (a) more stable as well as more accurate (b) less stable as well as less accurate (c) more stable but less accurate (d) less stable but more accurate Q27. Transfer function of a system is used to calculate (a) the steady state gain (b) the time constant (c) the order of the system (d) the output for a given input Q28. In a closed loop control system (a) control action depends upon the output and also on the input command (b) output signal is fed back to be compared with the reference signal (c) the accuracy is better than in the open loop system (d) all of the above Q29. The difference of the reference input and the actual output signal is called (a) error signal (b) controlling signal (c) actuating signal (d) transfer function Q30. If the transfer function of a system is (a) T (b) zero

,the steady state error to unit step input is (c) infinite (d) none of these

Q31. In a PID controller,the values of proportional, integral and derivative are dependent on (a) future, past and present errors respectively (b) present, past and future errors respectively (c) past, present and future errors respectively (d) present, future and past errors respectively Q32. The inverse Laplace transform of (a)

2(t+1)

(b)

2e-t

is (c)

2et

(d)

e-2t

Q33. The signal is extended from 96KHz to 100KHz, so the minimum sampling frequency required is (a) 8KHz (b) 200KHz (c) 4KHz (d) 100KHz Q34. A differentiation circuit has a (a) very high time constant (c) infinite time constant

(b) (d)

very low time constant zero time constant

Q35. Ideally Voltage Standing Wave Ratio (VSWR) should be (a) as large as possible (b) as small as possible (c) as close to unity as possible (d) infinity Q36. Following is/are a property/properties of quantization (a) it is an nonlinear process (b) it is an irreversible process (c) it maps a larger set of input (d) all of these values to a smaller set

Q37. Most commonly used filter in SSB generation are (a) mechanical filters (b) RC filters (c) LC filters

(d)

low pass filters

Q38. If the antenna diameter in a radar system is increased by a factor of 4, the maximum range will be increased by a factor of (a) 2 (b) 4 (c) 8 (d) 16 Q39. Following type of multiplexing cannot be used for analog signalling (a) FDM (b) TDM (c) CDM (d) None of these Q40. In TDM systems, channel separation is done with the use of (a) AND gates (b) band-pass filters (c) differentiator circuit (d) integrator circuit Q41. Data-link layer of the OSI model specifies (a) data link procedures that provide for the exchange of data via frames that can be sent and received (b) the interface between the X.25 network and packet mode device (c) the virtual circuit interface to packet-switched service (d) all of the above Q42. FDDI is a (a) ring network

(b) star network

(c) mesh network (d) bus based network

Q43. Which of the following TCP/IP protocol allows an application program on one machine to send a datagram to an application program on another machine? (a) UDP (b) VMTP (c) X.25 (d) SMTP Q44. The main difference between synchronous and asynchronous transmission is that (a) the clocking is derived from the data in synchronous transmission (b) the clocking is mixed with the data in asynchronous transmission (c) the pulse height is different (d) the bandwidth required is different Q45. Transducer is a device which (a) converts one form of power in to the other (b) is similar to transformer (c) converts one form of energy in to other (d) helps in measuring electricity Q46. Principle of hysteresis is not used in (a) electrical water geyser (b) electrical motor (c) multi-vibrators (d) Schmitt trigger Q47. Which of the following motors would not be suitable for use as servomotors? (a) AC induction motor (b) brushless AC motor (c) stepper motor (d) permanent magnet DC motor Q48. The stator of an induction motor is made of (a) carbon (b) wood (c) copper stampings (d) silicon steel laminators Q49. An ideal DC generator is one that has _____ voltage regulation (a) low (b) high (c) zero (d) positive Q50. Commutator is used in (a) DC generator (b) AC generator (c) invertors (d) convertors

AFCAT 1 2015 EKT EEE ELECTRICAL AND ELECTRONICS STREAM ANSWER KEYS: Question Number

Answer

Question Number

Answer

1

C

26

C

2

A

27

D

3

B

28

D

4

B

29

A

5

A

30

B

6

D

31

B

7

D

32

B

8

B

33

B

9

B

34

B

10

D

35

C

11

D

36

D

12

A

37

A

13

B

38

A

14

C

39

B

15

C

40

A

16

C

41

A

17

C

42

A

18

B

43

A

19

A

44

B

20

D

45

C

21

C

46

C

22

B

47

C

23

C

48

D

24

A

49

C

25

D

50

A

AFCAT 2 2015 EKT EEE ENGINEERING KNOWLEDGE TEST (EKT) ELECTRICAL AND ELECTRONICS STREAM

Q1.

What is the next number in the series 1,3,11,19,37,_____ (a) 55 (b) 41 (c) 56

(d)

None of the above

Q2.

A car travelled 75% of way from town A to town B at an average speed of 50 mph. The car travelled at the average speed of S mph for remaining part of the trip. The average speed for the entire trip was 40 mph . What is S? (a) 10 (b) 20 (c) 25 (d) 30

Q3.

If the area of the square is increased by 69% the side of the square increases by (a) 13% (b) 30% (c) 39% (d) 130%

Q4.

The value of Sin θ + Cosθ will be greatest when θ = (a) 30 (b) 45 (c) 60

(d)

90

Q5.

Out of the following pairs, choose the pair in which the physical quantities do not have identical dimension? (a) Pressure and Young's modules (b) Planck's constant and Angular momentum (c) Impulse and moment of force (d) Force and rate of change of linear Momentum

Q6.

Out of the following, which one is least commonly emitted by radioactive substance? (a) electrons (b) electromagnetic radiations (c) alpha particles (d) neutrons

Q7.

Sound produced at a point is heard by a person after 5 seconds, while the same sound is heard by another person after 6 seconds. If the speed of sound is 300 m/s, what could be the maximum and minimum distances between the two persons? (a) 1.8 km, 0.15 km (b) 2.2 km, 0.20 km (c) 2.8 km, 0.25 km (d) 3.3 km, 0.30 km

Q8.

The most electronegative element among the following is (a) sodium (b) bromine (c) fluorine

(d)

oxygen

Q9.

The nuclear particles which are assumed to hold the nucleons together are (a) electrons (b) positrons (c) neutrons (d) mesons

Q10.

The most abundant rare gas in the atmosphere is (a) He (b) Ne (c)

Ar

Quantizing noise occurs in (a) PCM (c) FDM

Time - division - multiplexer PPM

Q11.

Q12.

(b) (d)

(d)

Which of the following antennas is best excited from a waveguide? (a) Biconical (b) Horn (c) Helical (d)

Xe

Discone

Q13.

The peak transmitted power in a radar system is increased by a factor of 16 the maximum range will be increased by a factor of (a) 2 (b) 4 (c) 8 (d) 16

Q14.

The energy stored will be least in (a) coil (c) resistor

Q15.

(b) (d)

Thevenin’s theorem is applied to networks with (a) DC source only (b) (c) both AC & DC source (d)

capacitor same energy will be stored in all AC source only none of the above

Q16.

The Shannon’s Theorem sets limit on the (a) highest frequency that may be sent over channel (b) maximum capacity of a channel with a given noise level (c) maximum number coding levels in a channel (d) maximum number of quantizing levels in a channel.

Q17.

Maxwell’s electromagnetic equations are valid under all conditions except one that is (a) they do not apply to non-isotropic media (b) they do not apply to non-homogeneous media (c) they do not apply to media which move with respect to system coordinates (d) they do not apply to non-linear-media

Q18.

Given a carrier frequency of 100 KHz and a modulating frequency of 5KHz, the bandwidth of AM transmission is (a) 5KHz (b) 200KHz (c) 10KHz (d) 20KHz

Q19.

In a modulation system, if modulating frequency is doubled, the modulation index also becomes double, the system is (a) FM (b) AM (c) PM (d) both FM and AM

Q20.

The bandwidth requirement of a telephone channel is (a) 3KHz (b) 5KHz (c) 10KHz (d) 15KHz

Q21.

In class A operation of an amplifier the current flows through the active device for (a) whole of the input cycle (b) half of the input cycle (c) more than half of the input cycle (d) more than three fourth of the input cycle

Q22.

P Type Semiconductor material as a whole is (a) positively charged (b) (c) electrically neutral (d)

negatively charged dipole

Q23.

Hartley oscillator is (a) an inductively coupled oscillator (b) capacitor coupled oscillator (c) switchable for low frequencies (d) resistance coupled oscillator

Q24.

h parameters of a transistor (a) are constant (b) vary with temperature (c) are dependant upon collector current (d) none of the above

Q25.

The target cross section is changing, the best system for accurate tracking is (a) monopulse (b) conical scanning (c) sequential locking (d) lobe switching

Q26.

Waveguides are not used for frequencies below (a) 1GHz (b) (c) 100 Ghz (d)

10 GHz 500 Mhz

The unit of magnetic susceptibility is (a) Wb-m^2 (c) Wb/A-m

(b) (d)

Wb A-m Wb/m^2

Schmitt trigger can be used as a (a) comparator (c) flip flop

(b) (d)

square wave generator all of these

Q27.

Q28.

Q29.

For making a capacitor, it is better to select a dielectric having (a) high permittivity (b) low permittivity (c) same permittivity as that of air (d) very low permittivity

Q30.

The value of resistor creating thermal noise is doubled .the noise power generated is (a) halved (b) doubled (c) unchanged (d) tripled

Q31.

Subtracting 0101 from 1110 in binary terms, we get (a) 0110 (b) 1010 (c) 1001

Q32.

The universal gate is (a) AND (c) XOR

(b) (d)

(d)

0011

NOR NAND

Q33.

Fidelity in a communication receiver is provided by (a) mixer stage (b) detector stage (c) various amplifier section (d) audio stage

Q34.

The TWT is sometimes preferred to the magnetron as a radar transmitter outputtube because it is (a) capable of a longer duty cycle (b) a more efficient amplifier (c) more broadband (d) less noisy

Q35.

Modulation system used for video modulation in tv transmission is (a) DSB (b) VSB (c) SSB (d) SSBSC

Q36.

A yagi antenna produces (a) eight pattern (c) end fire array

(b) (d)

broadside pattern helical pattern

Medium frequency waves travel mainly as (a) sky waves (c) space waves

(b) (d)

surface waves ground wave

Q37.

Q38.

In a two cavity klystron , the input cavity resonator is also known as (a) velocity modulator (b) catcher cavity (c) buncher cavity (d) accelerator

Q39.

When the gate of a P- channel junction field effect transistor is more positive, the draincurrent (a) is increased (b) is reduced (c) remains unaltered (d) decreases

Q40.

Multiplication of 2 binary numbers A and B yields 11011; if A is 101 B is (a) 101 (b) 111 (c) 110 (d) none of these

Q41.

Which of the following can measure pressure directly? (a) LVDT (b) strain guage (c) Rotameter tube (d) bourdon tube

Q42.

The binary code of (21.125)10 is (a) 10101.001 (c) 10101.010

(b) (d)

10100.001 10100.111

Q43.

An op-amp zero crossing detector is basically_______converter (a) sine to square wave (b) square to sine wave (c) sine to sine wave (d) sine to triangle wave

Q44.

Which of the following is not a 8 bit microprocessor (a) INTEL8085 (b) MOTOROLA6800 (c) ZILOG280 (d) FAIRCHILD9440

Q45.

_________is used for keeping oscillator frequency away from any drift (a) PLL (b) VCO (c) comparator (d) frequency synthesizer

Q46.

__________ is also an active filter (a) RC filter (c) butterworth filter

(b) (d)

notch filter band pass filter

Q47.

In 8085 microprocessor ------is the highest priority interupt (a) INTR (b) RST5.5 (c) RST (d) trap

Q48.

In the standard TTL the totem pole stage refers to (a) the multi emitter I/p stage (b) phase splitter (c) o/p buffer (d) open collector o/p stage

Q49.

Decimal equivalent of hex no E5 is (a) 279 (c) 427

Q50.

(b) (d)

229 3000

Crossover distortion does not occur in __________ amplifiers. (a) push-pull (b) class-A (c) class-B (d) class-AB

ANSWER KEY: ELECTRICAL & ELECTRONICS 2 2O15 Question Number

Answer

Question Number

Answer

1

A

26

A

2

C

27

C

3

B

28

D

4

B

29

A

5

C

30

C

6

D

31

C

7

D

32

D

8

C

33

D

9

D

34

A

10

C

35

B

11

A

36

C

12

B

37

A

13

A

38

C

14

C

39

B

15

C

40

D

16

B

41

D

17

A

42

A

18

C

43

A

19

C

44

D

20

A

45

A

21

A

46

C

22

C

47

D

23

A

48

C

24

C

49

B

25

A

50

B

Engineering Knowledge Test eBook Electrical and Electronics

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