UNESCO-NIGERIA TECHNICAL & VOCATIONAL EDUCATION REVITALISATION PROJECT-PHASE II
NATIONAL DIPLOMA IN ELECTRICAL ENGINEERING TECHNOLOGY
Low
Low
High
_
I
10 10 Ohms Ohms
High
_
+
V
+
R
100 volts
ELECTRICAL ENGINEERING SCIENCE (I) COURSE CODE: EEC 115 YEAR I- SEMESTER I PRACTICAL Version 1: December 2008
TABLE OF CONTENTS WEEK 1: Basic Electrical quantities measurement measurement WEEK 2: Measurement of voltage and current WEEK 3: Measurement of resistance WEEK 4: Ohm’s law WEEK 5: Series circuit connections WEEK 6: Parallel circuit connections WEEK 7: Resistance in parallel WEEK 8: Capacitor in circuit WEEK 9: Voltage division principle WEEK 10: Series-parallel Series-parallel connected resistors WEEK 11: Kirchhoff’s current law WEEK 12: Kirchhoff’s voltage law WEEK 13: Resistivity WEEK 14: Power in d.c. circuit WEEK 15: Charging and discharging of a capacitor
TABLE OF CONTENTS WEEK 1: Basic Electrical quantities measurement measurement WEEK 2: Measurement of voltage and current WEEK 3: Measurement of resistance WEEK 4: Ohm’s law WEEK 5: Series circuit connections WEEK 6: Parallel circuit connections WEEK 7: Resistance in parallel WEEK 8: Capacitor in circuit WEEK 9: Voltage division principle WEEK 10: Series-parallel Series-parallel connected resistors WEEK 11: Kirchhoff’s current law WEEK 12: Kirchhoff’s voltage law WEEK 13: Resistivity WEEK 14: Power in d.c. circuit WEEK 15: Charging and discharging of a capacitor
Basic Electrical Quantities Measurement
Week 1
asur ement ment TITLE:- Basic El ectri cal Quan ti ties M easur
It is is necessary knowing how to measure voltage, current, and resistance. Special types of instruments are used to measure these basic electrical quantities. The instrument used to measure voltages is a voltmeter, the instrument used to measure current is a ammeter, and the instrument used to measure resistance is a o hmmeter.
Commonly, all three instruments are combined into a single instrument such as a multimeter or AVO meter ( Ampere- Volt-Ohmmeter), in which you can choose what
specific quantity to measure by selecting the switch setting. Figure (1) shows typical portable multimeters, part (a) from figure shows analog multimeter with pointer, and part (b) shows a digital multimeter with digital screen.
(a) Analog multimeter
(b) Digital multimeter
Figure (1) Typical portable Multimeter
General scheme symbols is used to indicate placement of meters in circuit when value changes need to be shown. Figure Figure (2) shows meter symbols used to present the different meters, as voltmeter, ammeter and ohmmeter.
1
Week 1
Basic Electrical Quantities Measurement
0.00 +
V
+
_
V
_
A
_
Ω
_
(a) Voltmeter 0.00 +
A
+
_
(b) Ammeter 0.00 + Ω
+
_
(c) Ohmmeter
Figure (2) Meter symbols
H ow to use Anal ogue meter : Figure (3) shows a typical multimeter. This device can measures the three electric quantities. The following step shows how to obtain readings from a multimeter.
1.Set the range of the desired quantity to be measured to the highest value. 2.Connect the leads to the right terminals at the meter 3.Switch on the circuit if necessary. 4.Adjust the range until you get clear readings. 5.Apply the following formula to obtain the measured quantity. Re ading
Range Full Scale
For example, referring to figure (3),the reading was 3.5 from a full-scale value of 5V, as shown in the small box.The range was set to
X300V.So
the measured voltage is
2
Week 1
Basic Electrical Quantities Measurement 3.5
6
300
5
8
10
210
12
4
14
2 20
30
200
500
ADC
100
1k
0
VDC
50
50
5k 20k
2
Scale
15
40
10
0
0
3
1
4
0
5
Ω
V AC
3 4
Reading =3.5
Pointer
Range
Off DC VOLT
600 300
600 300
60 12 0.3
60 12 3
x1 x10
0.06 DC Current
1.2 12 120
Common
AC VOLT
x100 x1k X100k
A
Ω
OHMS
V
Figure(3): Multimeter
Note: The scale has to be viewed from an angle perpendicular to it.
3
Measurement of Voltage and Current
Week 2
TITLE: M easur in g the Voltage Voltage can be considered as the pressure that force the electrons to flow. The voltage is being measured by measuring the difference between the voltages at the two terminals of the device-under-test which is the (voltage drop). This can be performed using a measuring instrument called voltmeter.
The voltmeter connection in the circuit is a parallel connection.
Figure (1) illustrates how to connect voltmeter in the circuit to measure the voltage across the resistor.
0.00 +
V
_
+
I
R
I
R
V
_ +
_
V
+
_
Figure (1) Example of a voltmeter connection
Procedure 1.
Adjust the range of the meter
2.
Connect the leads in the true terminals of the meter
3.
Apply the other ends of the leads to the resistor under test
4.
Record the reading and apply the formula
Re ading
Range full scale
4
Measurement of Voltage and Current
Week 2
M easur i ng Curr ent with A mmeter It is well known that current in the circuit is measured by ammeter, to measure the current , the circuit must be open and the ammeter is connected in series the circuit.
Procedure 1.
Connect the simple circuit shown in the figure below
2.
Open the circuit between the source and the resistor
3.
Connect the ammeter terminals to one end of the resistor and to the source
4.
Switch on the power supply and record the reading.
5.
Apply the formula
Re ading
Range full scale
if necessary
Note: If the meter did not give any movement or tried to move backward, then switch the terminal leads with each other
5
Measurement of Voltage and Current
Week 2
Figure(1) illustrates how to connect ammeter in the circuit and measure the current.
I
_
+
I
R
R
+
V
_
(a) Circuit in which the current is to be measured.
R
R
_
+
+
V
_
(b) Open the circuit between the resistor and the positive terminal of battery.
0.00 +
A
_
I
+
+
R
_
V
_
A
R
I
+
_
(c) Install the ammeter in the current pass with polarity as shown (negative to negative, positive to positive)
F igu r e 1: Ex ample of an ammeter connecti on
6
Measurement of Resistance TITLE:-
Week 3
Measuring Resistance with Ohmmeter
To measure resistance, connect the ohmmeter across the resistor. The resistor must first remove from the circuit. This procedure is shown in figure (2).
0.00 + Ω
_
+
R
R
Ω
_ +
_
V
+
_
Figure (2) Example of using ohmmeter Procedure
1.
Adjust the meter so that when the two terminals are short circuited, the ohmmeter reads zero
2.
Disconnect the resistor to be measured from the circuit (why?)
3.
Apply the meter leads to the resistor terminals (resistor is parallel to the meter)
4.
Record the reading and apply the formula
Re ading
Range full scale
if necessary
7
Ohm’s Law
Week 4
TITLE: Ohm's law OBJECTIVE:- Verification of Ohm’s Law
Ohm s law is the most important mathematical relationship between voltage, current ’
and resistance in electricity.
V = I X R
It is important to know how to read the resistors' colour code and hence its ohmic value. In the following figure it shows a table of the meaning of each colour. For example, for the resistor in the figure(1),the value of the resistor is 200kΩ,since the band 1 is red i.e. equivalent to 2 in the table ,band 2 is black equivalent to zero in the table and the band 3 is yellow indicating of a multiplier of 10,000.see at the bottom of the figure. The fourth band is the tolerance band i.e the percentage of error. It usually comes in two colors ,the silver indicates ±5% and the gold indicates ±10%.so for example, the value resistor will lie between 210kΩ and 190kΩ.
Procedure 1.
Select a number of different resistors
2.
Use the table below to determine their values
3.
Use ohmmeter to measure the same resistors you figured out
4.
Compare your calculated values with the readings you obtained
8
Ohm’s Law
Week 4
Resistor s color code:
Band2:Figure 2 Band 1:Figure 1
Multiplier
First figure Second value figure value
Colour
Tolerance
Multiplier
Black
0
0
X1
Brown
1
1
X10
Red
2
2
X100
Orange
3
3
X1000
Yellow
4
4
X10,000
Green
5
5
X100,000
6
6
X1,000,000
Violet
7
7
X10,000,000
Grey
8
8
X100,000,000
White
9
9
X1,000,000,000
Blue
2
0
X10,000=200K
5
F igu re 1: Resistors colou r code
9
Series Circuit Connection
Week
TITLE:- series circuit OBJECTIVE: verification of series circuit
There are three basic types of circuits, series, parallel and series-parallel circuits.
Ser ies cir cuit : Series circuit is the simplest circuit. The conductors, loads and power supply are connected with only one path for the current. The same amount of current will flow through each load. However, the voltage across each load will be different. Figure(1) shows different configuration of series circuits.
Procedure : 1.
Connect a number of resistors is series
2.
Measure the current in the circuit. What do you notice?
3.
Connect two identical lamps in series. Notice the brightness of the lamps
4.
Add one more lamp to the circuit you connected in step 3. What do you notice?
5.
Repeat step 4 with more lamps and measure the current in all cases
6.
Write a conclusion
10
Week
Series Circuit Connection A
B
A
B
The Electric Current
F igur e1 : D if ferent confi guration of seri es circuits
11
Parallel Circuit Connections
Week 6
TITLE: Parallel circui t: OBJECTIVE: To verify parallel circuit
The main difference between a series circuit and a parallel circuit is in the way the components are connected. Parallel circuit should have at least two loads connected separately to the voltage source, so the voltage across the loads are the same. However, in a parallel circuit the electric current has several paths that it can travel.
Figure(2) shows
different configuration of parallel circuits. Procedure
1.
Connect a number of resistors is parallel as shown below
2.
Measure the current in each branch and the total current. Comment on the readings
3.
Add more resistors in parallel. Repeat step 2
4.
Measure the voltage across each resistor. Comment on your results A
A
B
B
12
Parallel Circuit Connections A +
Week 6
A
IT
+
I1
I2
_
A
IT
I1 I2
IT
_
B
B
+
IT B
IT I2 I1
_
IT
Figure1: Differe
13
Resistance in Parallel
Week 7
TITLE:- Resistance of parallel connected resistors
OBJECTIVE: To verify parallel connection circuits 1. To measure the total resistance of combinations of parallel connected resistors .
A parallel circuit is a circuit with more than one path for current flow. Removing one branch of a parallel circuit does not affect the operation of (the current in) the remaining branch circuit. The total resistance of parallel connected resistors is less than the resistance of smallest branch resistor. There are many parallel circuits in electronic equipment. The formula for calculating R T for parallel resistors is:
1/R T = 1/R 1 + 1/R 2 + 1/R 3 +……..+ 1/R n
R T = R 1xR 2xR 3 / R 1R 2+R 2R 3+R 3R 1
Materials Required: Multi-meter. Resistors: all ½ watt, 330 Ω, 470 Ω, and two 1200 Ω.
Procedure: 1) Refer to the following figure choose the resistors shown as combination A. 14
Resistance in Parallel
Week 7
2) Measure the resistance of each of the resistors supplied for combination A. Record the measured value of each resistor in the column beneath is colour coded value in the following table. 3) Measure the R T of the parallel combination and record your reading in the column label “Measured R T “in the following table.
Ohmmeter
Parallel Combination Group A Group B Group C
Colour coded value Measured value, Ω Measured value, Ω Measured value, Ω
R 1
R 1
R 1
R 1
330 Ω
470 Ω
1200 Ω
1200 Ω
X
X
Measured R T Ω
X X
X
Questions: Q1) was the value R T greater or smaller than the value of the smallest branch resistor in each combination?
Q2) Combination (group C) placed two resistors of equal value in parallel. From the results of measuring R T of this combination of resistors, suggest a general rule for R T of any two resistors of equal value connected in parallel. 15
Resistance in Parallel
Week 7
Q3) what is the R T of three 330 Ω resistors in parallel?
Variable Resistors. Objective:
To measure resistance between the variable (centre terminal) and the terminals on other side of it as the shaft of a potentiometer is turned from its minimum to maximum position.
Materials Required: 1) Multi-meter. 2) Variable Resistor 10000 Ω Potentiometer.
Procedure: 1. Examine the potentiometer assigned to you. Place it so that the shaft points toward you. Measure and record in the following table the value of potentiometer between the two outside terminals. 2. Turn the shaft to any position (1) and measure the resistance between the left terminal (A) and the centre terminal (C) Record this reading in the following table . 3. Without moving the shaft, measure the resistance between the right terminal (B) and the centre terminal (C), Record this reading R BC in the table. 4. Complete the table.
16
Resistance in Parallel
Week 7
A
C B
Table 6.1
Step
Potentiometer shaft setting
R AB Ω
1
Any
2
Position 1
X
3
Position 2
X
4
C.W
X
5
C.C.W
X
R AC Ω
R BC Ω
R AC + R BC
X
X
X
Questions: Q1) In the potentiometer above, what is the relation between R AC, R BC, and R AB? Do your measurements confirm this relation?. Q2) In what position of the shaft is the resistance between A and B minimum?. Q3) In what position of the shaft is the resistance between.
17
Week 8
Capacitor TITLE: Capacitor in a circuit
OBJECTIVE: To test capacitor by observing their charging and discharging using an ohmmeter.
Capacitor is a device that stores energy in the electric field created between a pair of conductors on which equal but opposite electric charges have been placed. Capacitance is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol (F). However 1F is very large, so prefixes are used to show the smaller values. Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico): -6
µ means 10 (millionth), so 1000000µF = 1F
n means 10 (thousand-millionth), so 1000nF = 1µF
-9
-12
p means 10 (million-millionth), so 1000pF = 1nF
Materials Required:
Ohmmeter. Capacitor.
Fig 8.1
18
Week 8
Capacitor Procedure: 1. Connect the circuit as shown above.
2. Read the ohmmeter and record the conditions of the capacitor which are:
a. If the ohmmeter reading move toward zero and then slowly returns to infinity means the capacitor is in a good condition. b. If the ohmmeter move towards zero and remain at zero means the capacitor is short circuited . c. If the reading doesn’t change and remains at infinity me ans the capacitor is open circuited.
3. Replace the capacitor and repeat step 1 and 2. 4. Repeat step 3 until all capacitors are tested.
Table 8.1
Capacitor
Reading
Remark
Answer the following
C1
questions:
Q1) What
C2
is the meaning of capacitanc
C3
e? Q2) Draw the symbol 19
Week 8
Capacitor of a capacitor? Q3) State 1 application for capacitors? Q4) complete the following:
If the ohmmeter reading move toward zero and then slowly returns to infinity means ………………………
the ohmmeter move towards zero and remain at zero means …………………………
If the reading doesn’t change and remains at infinity means …………
20
Voltage Division Principle
Week 9
TITLE: Voltage divider OBJECTIVE: Verify the operation of voltage divider APPARATUS:
(1)
2 Digital multimeters
(2)
Variable power supply
(3)
Resistor R 1 = 330 Resistor R 2 = 1K Resistor R 3 = 500 - Trimmer
PROCEDURES:
(1)
Connect a digital multimeter as d.c voltage, and another one as milliammeter fig 9.1
(2)
Set the switch S1 to OFF
(3)
Adjust the voltage to 5V by turning the variable power supply
(4)
Read the value of the voltage V0 (no load) between point 3 and earth and write it down in table 9.1
(5)
Calculate the value of the voltage V0 (no load) and write it in table 9.1
(6)
turn the trimmer R 3 completely clockwise
(7)
Set the switch S1 to ON
(8)
Read the values of the voltage and of the current and write them in table 9.1
(9)
Repeat the previous operation for all the values of R 3 shown in table 9.1
(10)
Represent in fig 9.2 the characteristic curve voltage-current of the voltage divider
(11)
Comment on the results
21
Voltage Division Principle
R 1
1
Week 9
2
3 S1
ON ON
A
com
R 2
VS
R 3
V
A
Voltmeter
com
Milliammeter Fig 9.1
Table 9.1: Obtained Results
V0(no load [V] Measured
V0(no load) [V] calculated
R 3 []
500 400
300
200
100
0
V0 [V]
I0[mA]
V0(V)
I0(mA)
Fig 9.2 22
Series-Parallel Connection of Resistors
Week 10
TITLE: Series-Parallel Resistors OBJECTIVES: Observe the behaviour of series-parallel connected resistors APPARATUS: (1)
Digital multimeter
(2)
Resistor R 1 = 1K 5% Resistor R 2 = 1K 5% Resistor R 3 = 220K 5%
PROCEDURE: (1)
Set the switches S1 and S2 to ON
(2)
Connect a multimeter, set as ohmmeter, fig 10.1
(3)
Write down in table 10.1 the value read in the ohmmeter
(4)
Calculate the value of the resistance R 12 and write down the value in table 10.1
(5)
Compare the measured value with the calculated one
(6)
Move a terminal of the ohmmeter from the jack 2 to the jack 1
(7)
Set the switches S1 to ON, and S2 to OFF
(8)
Write down in table 10.1 the value read in the ohmmeter
(9)
Calculate value of the resistance R 13 and write down the value in table 10.1
(10)
Compare the measured value with the calculated one
(11)
Set the switches S1 and S2 to ON
(12)
Write down in table 10.1 the value read in the ohmmeter
(13)
Calculate the value of the resistance R e and write down the value in table 10.1
(14)
Comment on the measured value with calculated one
23
Series-Parallel Connection of Resistors
1
R 3
Week 10
2
R 2
R 1 ON
com
V
S1
S2
Fig 10.1
Table 10.1: Obtained Results
R 12 [ ]
R 12 [ ]
R 13 [ ]
R 13 [ ]
R e [ ]
R e [ ]
Measured
calculated
Measured
Calculated
Measured
Calculated
24
Kirchhoff’s Laws
Week 11
TITLE:- Kirchhoff’s Current |Law OBJECTIVE: To verify Kirchhoff’s law APPARATUS : (1)
Variable power supply
(2)
Voltmeter
(3)
Milliameter
(4)
Resistor R 1 = 1K 5% Resistor R 2 = 1K 5% Resistor R 3 = 220K 5%
PROCEDURES:(1)
Connect multimeter, set as a d.c voltmeter, and another one as milliameter, Fig 11.1
(2)
Adjust the voltage to 10V by turning the variable power supply
(3)
Set the switches S1 to On, S2 and S3 to OFF.
(4)
Write down in table 11.1 the values read on the voltmeter and on the milliammeter.
(5)
Set the switches S2 to ON, and S1 and S2 to OFF
(6)
Write down in table 11.1 the values read on the voltmeter and on the Milliammeter
(7)
Set the switches S3 to ON, S1 and S2 to OFF
(8)
Write down in table 11.1 the values read on the voltmeter and on the milliammeter
(9)
Calculate the value of the current in the single resistors and write down the results in table 11.1
(10)
Compare the calculated values with the measured ones.
(11)
Verify that the sum of the current that go in the node 2 is equal to the sum of the current that go out.
(12)
Comment on the result in steps (10) and (11)
25
Kirchhoff’s Laws
Week 11
2
2
1
S1
2
S2
S3 ON
ON
Fig 11.1 R 1 com
R 3
R 2
com
A
V
Fig 11.1
Voltmeter
Millammeter
Tabl e 11.1: Obtained Results
VR 1
I1
VR 2
I2
VR 3
I3
I1
I2
I3
[V]
[mA]
[V]
[mA]
[V]
[mA]
[mA]
[mA]
[mA]
Measured Value
I=0
Calculated value
26
Kirchhoff’s Laws
Week 12
TITLE:- Kirchhoff’s Voltage Law OBJECTIVE:- To verify Kirchhoff’s Voltage law APPARATUS: (1)
Variable power supply
(2)
Voltmeter X 2
(3)
Resistor R 1 = 100 5% Resistor R 2 = 220 5% Resistor R 3 = 330 5%
PROCEDURE: (1)
Use two Multimeters, set as dc voltmeters and connect them as it is shown in figure 12.1
(2)
Set the switches S1, S2 and S3 to ON
(3)
Adjust the voltage to 10V by varying the variable power supply
(4)
Write down in table 12.1 the values read on the voltmeters
(5)
Move the terminal of the voltmeter 2 on the terminals of the resistance R L (Jacks 4 and 5), measure the voltage drop and write down the value in Table 12.1
(6)
Move the terminals of the voltmeter 2 on the terminals of the resistance R 3 (Jacks 6 and earth), measure the voltage drop and write down the value in table 12.1
(7)
Verify that the sum of the voltage drops on the resistors corresponds to the voltage VS.
(8)
Calculate the value of the voltage drops on the resistors and write down the value in table 12.1.
(9)
Comment on the results in steps (7) and (8).
29
Kirchhoff’s Laws
1
R 1
2
3
S2
4
VS
ON
A
S1
Week 12
com
ON
A
V
6 Voltmeter 1
com
V
5
S3
R 2
R 3
Voltmeter 2
Fig 12.1
Table 12.1: Obtained Results
Vs (v)
VR 1 (V)
VR 2 (V)
VR 3 (V)
VR 1 (V)
VR 2 (V)
VR 3 (V)
V = VR 1 + VR 2 + VR 3 (V)
Measured
Measured value
Calculated value
Measured/Calculated
30
Week 13
Resistivity TITLE:- Resistivity of a material OBJECTIVE:- To verify resistivity of a material APPARTUS:(1) (2) (3) (4)
A length of a given resistance wire Digital multimetre Metre rule Micrometer gauge
PROCEDURE:(1) (2)
Measure the length of the given resistance wire Measure the diameter, d of the material by a micro meter gauge
(3) (4)
Compute the cross sectional area using the formula A = d /4 Set the digital multimetre to a suitable ohmmeter range and connect across the resistance wire at various lengths as shown in fig 13 .1 below S tart with a length of 10cm, 20cm, etc and tabulate the result in the form shown in the table below.
(5)
(6) (7)
2
2
Plot a graph of RA ( nm ) against L(cm) and find the slope of the graph. Comment on the results in step 6.
Table 13.1 L(cm)
R( )
d(mm)
2
A(nm )
2
RA( nm )
10 20 30 40 50 60 70 80 90
18
Week 13
Resistivity
0
10
20
30
40
50
60
70
80
90
Meter rule
Resistance wire
Multimeter
Fig 13.1 Probe
Fig 13.1
19
Power in d.c. Circuit
Week 14
TITLE:- Experimental determination of power in a d.c circuit OBJECTIVE:- To determine the power in a d.c circuit. BACKGROUND INFORMATION
The power of a resistor can be determined in a dc circuit under any of the following conditions: (1) if the resistance of the resistor is unknown, but the voltage (V) across the resistor and current (I) through the resistor can be measured. i.e Power P = IV, watts. (2) if the resistance (R) if the resistor and the current through it are known to give, 2 P = I R (watts). (3) if the resistance (R) of the resistor and the voltage across it are known to give 2 P = V /R (watts) PROCEDURE:
(1) (2) (3)
Connect the circuit shown in fig 14.1 with the voltmeter V across the resistor R and the ammeter A in series with it. Use the ammeter to record the current, I (Ampere) through the resistor and the voltmeter to record the P.d. (volts) across the resistor. Determine and record the value of R (in ohms) before the commencement of the experiment.
V
Voltmeter
R
E
A
Ammeter
R
Fig 14.1
31
Power in d.c. Circuit
Week 14
RESULT ANALYSIS:-
Calculate the power P, across the resistor using each and all the formulae stated above.
32
