MULTIPLE CHOICE QUESTIONS WITH ANSWERS ON POWER ELECTRONICS AND DRIVES
[Q-1] Silicon based rectifiers are preferred than germanium based rectifiers because (a) Si is available easily compared to Ge (b) Only Si has a stable off state (c) Ge is very temperature sensitive (d) Si only has the characteristics 1 ! " # 1 at lo$ collector currents and reaches 1 at high currents %hich of the above above statements statements are true& Options' 1 * +* , " +* , + Only . , Only / 0one of the above options Ans: 2
[Q-"] n a triac* (a) 2he triggering pulse to main terminal 1 should be of the same polarity as the anode potential bet$een 321 and 32" (b) 2he triggering pulse should be of opposite polarity to that of anode potential (c) %hen the triggering pulse is positive and anode is positive* it is operating in the first 4uadrant (d) %hen the triggering pulse is negative and anode is negative its sensitivity is highest %hich of the above above statements statements are true& Options' 1 * , " * 5 5* , . * 5* , / 0one of the above options Ans: 4
[Q-] n a single phase full $ave S56 circuit $ith 6* 7 load (a) 8o$er is delivered to the source for firing angle of less than 9:; (b) 2he scr changes from inverter to converter at < 9:; (c) 2he negative dc voltage is ma=imum at < 1>:; (d) 2o turn off the scr* the ma=imum delay angle must be less than 1>:; %hich of the above above statements statements are true& Options' 1 5* , " 5 Only , Only . * + / 0one of the above options Ans: 1
[Q-.] %hile comparing triac and scr* (a) +oth are unidirectional unidirectional devices (b) 2riac re4uires more current for turn on than scr at a particular voltages (c) triac has less time for turn off than S56 (d) +oth are available $ith comparable comparable voltage and current ratings %hich of the above above statements statements are true& Options' 1 * 5 " +* 5 * + . , Only / 0one of the above options Ans:2
[Q-/] %hich of the follo$ing statements statements are true (a) f the S56* even $ith proper gate e=citation and anode-cathode anode-cathode voltage does not conduct for a particular load resistance* then it $ould be necessary to decrease the load resistance to turn O0 the S56 (b) 2he S56 $ould be turned O?? by voltage reversal of the applied anode-cathode ac supply of fre4uencies up to :@AB
[Q-] n a single phase full $ave S56 circuit $ith 6* 7 load (a) 8o$er is delivered to the source for firing angle of less than 9:; (b) 2he scr changes from inverter to converter at < 9:; (c) 2he negative dc voltage is ma=imum at < 1>:; (d) 2o turn off the scr* the ma=imum delay angle must be less than 1>:; %hich of the above above statements statements are true& Options' 1 5* , " 5 Only , Only . * + / 0one of the above options Ans: 1
[Q-.] %hile comparing triac and scr* (a) +oth are unidirectional unidirectional devices (b) 2riac re4uires more current for turn on than scr at a particular voltages (c) triac has less time for turn off than S56 (d) +oth are available $ith comparable comparable voltage and current ratings %hich of the above above statements statements are true& Options' 1 * 5 " +* 5 * + . , Only / 0one of the above options Ans:2
[Q-/] %hich of the follo$ing statements statements are true (a) f the S56* even $ith proper gate e=citation and anode-cathode anode-cathode voltage does not conduct for a particular load resistance* then it $ould be necessary to decrease the load resistance to turn O0 the S56 (b) 2he S56 $ould be turned O?? by voltage reversal of the applied anode-cathode ac supply of fre4uencies up to :@AB
(c) f the gate current of the S56 is increased* then the for$ard brea@do$n voltage $ill decrease Options 1 * +* 5 " +* 5 * 5 . * + / 0one of the above options Ans: 3
[Q-C] %hich of the follo$ing statements are true %hen gate triggering triggering is employed* a S56 S56 can $ithstand $ithstand higher values of diDdt* if the 1 Gate current is increased " 6ate of rise of gate current is increased Gate current is increased . 6ate of rise of gate current is decreased O82O0S' (a) * . (b) 1* . (c) "* (d) 1* " (e) 0one of the above options Ans: A
[Q-E] n a S56 based converter* the free $heeling diode is used to (a) dd to the conduction current of thyristors (b) Oppose the S56 conduction (c) 5onduct current during the O?? period of the S56 (d) 8rotect the S56 by providing a shunt path Ans:C
Power Electronics Objectie Q!estions wit" Answers# [1] " Six MOSFETs connected in a bridge configuration (having no other power device) MUST be operated as a Voltage Source Inverter (VSI) ". This statement is [GATE-2007]
A. True, because being majority carrier devices, MOSFETs are voltage driven B. True, because MOSFETs have inherently anti parallel diodes C. False, because it can be operated both as current source Inverter (CSI) or a VSI D. False, because MOSFETs can be operated as excellent constant current sources in the saturation region
Ans: D
[2] A single phase full - wave half controlled bridge converter feeds an inductive load. The two SCRs in the converter are connected to a common DC bus. The converter has to have a free wheeling diode [GATE-2007] A. because the converter inherently does not provide for free wheeling B. Because the converter does not provide for free wheeling for high values of triggering angles C. Or else the free wheeling action of the converter will cause shorting of the AC supply D. Or else if a gate pulse to one of the SCRs is missed, it will subsequently cause a high load current in the other SCR
Ans: B
[3] The power electronic converter shown in the figure has a single pole double throw switch. the pole P of the switch is connected alternately to throws A and B. The converter shown is a [GATE-2010]
A. Step down chopper( buck converter) B. Half- wave rectifier C. Step Up chopper ( boost converter) D. Full wave converter
Ans: A [5] The fully controlled thyristor converter in the figure is fed from a singlephase source. When the firing angle is 0 , the dc output voltage of the converter is °
300 V. What will be the output voltage for a firing angle of 60 , assuming °
continuous conduction? [GATE-2010]
(A) 150V (B) 210V (C) 300V (D) 100πV
Ans: A Answer
[6] The manufacturer of a selected diode gives the rate of fall of the diode current di/dt = 20 A/ms, and a reverse recovery time of trr =5 ms. What is value of peak reverse current?
Ans: 44.72A
The peak reverse current is given as:
The storage charge QRR is calculated as Qrr = (1/2)*(di/dt)* SQU.(trr) = 1/2 X 20A/uS X 5u X 5u = 50uC. substitute the Qrr value in Irr equation.
[8] Circuit turn-off time of an SCR is defined as the time [GATE2011] A. Taken by the SCR to turn off B. Required for SCR current to become zero C. For which the SCR is reverse biased by the commutation circuit D. For which the SCR is reverse biased to reduce its current below the holding current
Ans: C
[9] A single phase fully controlled thyristor bridge ac-dc converter is operating at a firing angle of 25 degree, and an overlap angle 10 degree with constant dc output current of 20A. The fundamental power factor ( displacement factor) at input ac mains is [GATE2007] A. 0.78 B. 0.827 C. 0.866 D. 0.9
Ans:A
[10] A three phase fully controlled thyristor bridge converter is used as line commutated inverter to feed 50 KW power at 420 V DC to a three phase 415V(line), 50Hz as mains. Consider Dc link current to be constant. The rms current of the thyristor is A. 119.05A B. 79.37A C. 68.73A D. 39.68A
Ans:D
[GATE2007]
[1] In a uniform electric field, field lines and equipotentials [Gate 1997 ] a Are parallel to one anot!er " Intersect at #$ de% c Intersect at &' de% d Are ort!o%onal Ans:D
[(] )or a pulse transformer, t!e material used for its core and t!e possi"le turn ratio from prima* to secondar* are respecti+el* a ferrite- (':1 " laminated iron- 1:1 c ferrite- 1:1 d po.dered iron- 1:1 Ans: C
[&] /!e capacitance of a re+erse "iased 0unction of a t!*ristor is (' picofarad /!e c!ar%in% current of t!is t!*ristor is #mA /!e limitin% +alue of d+2dt is 32u4 Ans:200
[#] 5!en t!e induction motor runs at s*nc!ronous speed t!e +olta%e induced in t!e rotor of it is a 3er* near input +olta%e to stator " 4lip time t!e input +olta%e c 6ero d one of t!e a"o+e Ans:C
[$] C!opper control for t!e DC motor pro+ides +ariation in a Input +olta%e " )requenc* c one of t!e a"o+e Ans: A
[8] 5!ile comparin% 4C .it! B/, .!ic! of t!e follo.in% is true a 4C requires turn off circuit .!ile B/ does not " /!e +olta%e drop of 4C is less t!an B/ c 4C requires a continuous %ate current d B/ dra.s continuousl* "ase current
5!ic! of t!e a"o+e statements are true; 1 a onl* ( d onl* & a, d # ", d Common Data In t!e &?p!ase in+erter circuit s!o.n, t!e load is "alanced and t!e %atin% sc!eme is 1>'@?conduction modeAll t!e s.itc!in% de+ices are ideal
[7] /!e rms +alue of load p!ase +olta%e is [GA/('1(] a 1'813 " 1#1#3 c (1((3 d (>(>3 Ans: B
[>] If t!e dc "us +olta%e 3 d&''3, t!e po.er consumed "* &?p!ase load is [GA/('1(] a 1$5 " ('5 c ($5 d &'5 Ans: D
[9] /!e t*pical ratio of latc!in% current to !oldin% current in a ('A t!*ristor is [GA/ ('1(] a $' " (' c 1' d '$
Ans: B
[1'] A !alf?controlled sin%le?p!ase "rid%e rectifier is suppl*in% an ? load It is operated at a firin% an%le E and t!e load current is continuous /!e fraction of c*cle t!at t!e free.!eelin% diode conducts is [GA/ ('1(] a 12( " 1?E2π c E2(π d E2π Ans: D
[11] )or po.er factor correction of po.er s*stems .!ic! one is used: a capacitor " inductor c resistors Ans: A
[1(] 5!ic! t*pe of motor used a capacitor " s!aded c uni+ersal 4FI/ FA4 CAFACI/H H/H
in
!ome
pole
ceilin%
fan: motor motor motor
Ans: A
[1&] Hp?amp operational amplifier a " c elati+e d 4ame output resistance
input
resistance: 6ero Infinit* resistance
Ans:B
[1#] )or an in+erter op?amp, .!at .ill "e t!e equi+alent output resistance; a 6ero " Infinit* c elati+e for.ard resistance d 4ame as t!e input resistance Ans: A
SOLVED OBJECTIVE QUESTIONS FROM DC MACHINES:
[1] Voltage equation of a dc motor is A. V = Eb + IaRa B. Eb = V + IaRa C. V = Eb/IaRa D. V = Eb + Ia2Ra E. None of the above Ans: A [2] Both Hopkinson's test and Field test A. Require two electrically coupled series motors B. Need two similar mechanically coupled motors C. Use negligible power D. Are regenerative tests E. None of the above Ans:B [3] which of the following motor has the constant speed? A. Series motor B. Shunt motor C. Cumulatively compound motor D. All of the above E. None of the above Ans:B 4] The usual test to find the efficiency of the traction motor is A. Field's test B. Retardation test C. Hopkinson's test D. Swinburn's test E. None of the above Ans: A [5] A DC series motor is best for driving A. Lathes B. Cranes and hoists C. Shears and punches D. Machine tools E. None of the above Ans: B
[6] Retardation test on a dc shunt motor is used for finding A. Stray loss B. Copper loss C. Friction loss D. Iron loss E. None of the above Ans: A [7] In a DC series motor increasing the load current will A. Decrease the speed B. Increase the speed C. Better commutation D. Increase the back emf E. None of the above Ans: A [8] One of the main advantage of the swinburn's test is A. It is applicable both shunt and compound motors B. It needs one running test C. It is very economical and convenient D. It ignores any charge in iron loss E. None of the above Ans:C [9] the main disadvantage of hopkinson's test for finding efficiency of shunt dc motors is that it A. Requires full load power B. Ignores any change in iron loss C. Needs one motor and one generator D. Requires two identical shunt machines E. None of the above
Ans D [10] The most economical method of finding no losses of a large dc shunt motor is A. Hopkinson's test B. Swinburn's test C. Retardation test D. Field's test E. None of the above
Ans: B
SYNCHRONOUS MOTOR OBJECTIVE QUESTIONS WITH ANSWERS:
[1] In a s*nc!ronous motor, damper .indin% is pro+ided to A 4ta"iliJe rotor motion B 4uppress rotor oscillations C De+elop necessar* startin% torque D Bot! B and C Ans: D
[(] 4*nc!ronous capacitor is A An ordinar* static capacitor "an B An o+er eKcited s*nc!ronous motor dri+in% mec!anical load C An o+er eKcited s*nc!ronous motor runnin% .it!out mec!anical load D one of t!e a"o+e Ans:C
[&] A s*nc!ronous mac!ine is called as dou"l* eKcited mac!ine "ecause A It can "e o+er eKcited B It !as t.o sets of rotor poles C Bot! its rotor and stator are eKcited D It needs t.ice t!e normal eKcitin% current Ans: C
[#]If t!e field of a s*nc!ronous motor is under eKcited, t!e po.er factor .ill "e A a%%in% B eadin% C Lnit* D ore t!an unit* Ans: A
[$] /!e direction of rotation of a s*nc!ronous motor can "e re+ersed "* re+ersin% A Current to t!e field .indin% B 4uppl* p!ase sequence C Folarit* of rotor poles D one of t!e a"o+e Ans: B
[8]A s*nc!ronous motor connected to infinite "us"ars !as at constant full?load, 1''M eKcitation and unit* pf Hn c!an%in% t!e eKcitation onl*, t!e armature current .ill !a+e A eadin% pf .it! under?eKcitation B eadin% pf .it! o+er eKcitation
C a%%in% pf .it! o+er eKcitation D o c!an%e of pf Ans: B
7] /!e maKimum +alue of torque an%le a in a s*nc!ronous motor isde%rees electrical A #$ B 9' C Bet.een #$ and 9' D Belo. 8' Ans: B
[>] /!e an%le "et.een t!e s*nc!ronous rotatin% stator fluK and rotor poles of a s*nc!ronous motor is A 4*nc!roniJin% an%le B /orque an%le C Fo.er factor an%le D 4lip an%le Ans:B
[9] In a s*nc!ronous mac!ine .!en t!e rotor speed "ecomes more t!an t!e s*nc!ronous speed durin% !untin%, t!e dampin% "ars de+elop A 4*nc!ronous motor torque B DC motor torque C Induction motor torque D Induction %enerator torque Ans: D
[1'] 5!en load on a s*nc!ronous motor is increased its armature current is increased pro+ided it is A ormall* eKcited B H+er eKcited C Lnder eKciter D All of t!e a"o+e Ans:D
MEASUREMENTS AND INSTRUMENTATION O$%ECTIVE QUESTIONS WITH ANSWERS
[1] A rectifier t*pe instrument is connected to 1''3DC and is operated in t!e DC measurin% module reads a 1113 " 9'3
c $'3 d 1''3 Ans: A
[(] A permanent ma%net mo+in% coil ammeter !as a coil resistance of 99o!m and )ull 4cale Deflection)4D current of '1mA 4!unt resistance is 1 o!m Current t!rou%! t!e meter at '$ )4D is a '''7mA " ''$mA c ''(&mA d '1mA Ans: B
[&] Hne sin%le p!ase .attmeter operatin% on (&'3 and $A for $ !ours maes 19#' re+olutions eter constant in re+olutions is #'' 5!at is t!e po.er factor of t!e land; a 1 " '># c '7& d '8$ Ans:B
[#] )or po.er measurement of t!ree p!ase circuit "* t.o .attmeter met!od, .!en t!e +alue of po.er factor is less t!an '$ la%%in% a one of t!e .attmeters .ill read Jero " "ot! %i+e t!e same readin%s c one of t!e .attmeter connections .ill !a+e to "e re+ersed d pressure coil of t!e .attmeter .ill "ecome ineffecti+e Ans:C
[$] 5!en usin% o!mmeter, applied +olta%e is to "e disconnected from t!e circuit "ecause a 3olta%e source .ill increase resistance " Current .ill decrease resistance c t!e o!mmeter !as its o.n internal "atter* d non of t!e a"o+e Ans: C
[8] 5!ic! .a+e !as t!e least form factor; a 4quare .a+e " ectan%ular .a+e
c 4ine .a+e d /rian%ular .a+e Ans: A
[7] 5it! a s.eep time 1'ms across t!e screen t!e approK !oriJontal sa.toot! frequenc* .ill "e a $'J " 1''J c 1J d $''J Ans: B
[>] A sprin% controlled indicatin% instrument !as a deflection of 9'de% for maKimum current I /!e correspondin% deflection for a %ra+it* controlled instrument is a 9'@ " 1('@ c &'@ d '@ Ans: C
[9] It is found t!at 1'A current passes t!rou%! a resistor of 1'o!ms /!e resistor !as $M tolerance /!e error in measurement of current can "e as !i%! as $M 5!at is maK error in measurement of po.er, calculated from measured +alue of I and t!e nominal +alue of resistor; a 1'' 5 " 1$'5 c$'5 d (''5 Ans: B
[1'] A resistor of 1'No!ms .it! $M tolerance is connected in parallel .it! a $No!ms resistor of 1'M tolerance 5!at is t!e tolerance limit for t!e parallel net.or; a $M " 887M c 1'M d >&&M Ans: D
[11] /!e resistance offered to t!e passa%e of an in?+ar*in% current "* a column of mercur* at t!e temperature of meltin% ice of mass 1##$(1 %ms of uniform cross?
sectional area and len%t! 1'8&cm is a 4tandard o!m " Hne international o!m c Hne o!m accordin% to 4I units d Hne o!m accordin% to .orin% standards Ans: B
Electric&l M&c"ines ' Altern&tors # P&rt ( [1] Squirrel cage bars placed in the rotor pole faces of an alternator help reduce hunting (a) Above synchronous speed only (b) Below synchronous speed only (c) Above and blow synchronous speeds both (d) None of the above Ans: C
[2] The stationary alternator should not be connected to live bus-bars because it (a) Is likely to run as synchronous motor (b) Will get short - circuited (c) Will decrease bus - bar voltage though momentarily (d) Will disturb generated emf's of other alternators connected in parallel. Ans:B
[3] With a unity load p.f, the effect of armature reaction on the main field flux of an alternator is (a) Distortional (b) Magnetising (c) Demagnetising (d) Nominal Ans: A
[4] At lagging loads, armature reaction in an alternator is (a) Cross-magnetising (b) Demagnetising (c) Non-effective (d) Magnetising Ans:D
[5] The frequency of voltage generated by an alternator having 4 poles and rotating at 1800 rpm is (a) 60 Hz (b) 7200 Hz (c) 120 Hz (d) 450 Hz Ans: A
[6] The main disadvantages of using short pitch winding in alternators is that it (a) Reduces harmonics in the generated voltage (b) Reduces the total voltage around the armature coils (c) Produces asymmetry in the three phase windings (d) Increases Cu of end connections. Ans: B
[7] Zero power factor method of an alternator is used to find its (a) Efficiency (b) Voltage regulation
(c) Armature resistance (d) Synchronous impedance Ans: B
[8] Armature reaction in an alternator mainly affects (a) Rotor speed (b) Terminal voltage per phase (c) Frequency of armature current (d) Generated voltage per phase Ans: D
[9] The effect of increasing air gap length in the induction motor will increase the (a) Power factor (b) Speed (c) Magnetising current (d) Air gap flux Ans: C
[10] The principle of operation of a 3 phase induction motor is most similar to that of a (a) Synchronous motor (b) Repulsion start induction motor (c) Transformer with a shorted secondary (d) Capacitor start, induction run motor
Ans: C
BA4IC C/HIC4 L/IF CHIC
[1] A net.or desi%ned to pass si%nals .it! all frequencies eKcept t!ose "et.een t.o specified cut?off frequencies is called a a lo.?pass filter " !i%!?pass filter c "and?pass filter d "and?stop filter Ans: D
[(] A lo.?pass /?connected s*mmetrical filter section !as an inductance of (''m in eac! of its series arms and a capacitance of '$ O) in its s!unt arm /!e cut?off frequenc* of t!e filter is a 1''7 J " ($18 J c 711> J d 1779 J Ans: C
[&] A lo.?pass π?connected s*mmetrical filter section !as an inductance of (''m in its series arm and capacitances of #'' p) in eac! of its s!unt arms /!e cut?off frequenc* of t!e filter is a ($18 J " 8(9 J c 1779 J d &$$9 J Ans:A
[#] A !i%!?pass /?connected s*mmetrical filter section !as capacitances of #'' n) in eac! of its series arms and an inductance of (''m in its s!unt arm /!e cut?off frequenc* of t!e filter is a 1$9( J " 11($ J c (>1 J d &9> J Ans:D
[$] A !i%!?pass π?connected s*mmetrical filter section !as a capacitance of $''' p) in its series arm and inductances of $'' O in eac! of its s!unt arms /!e cut?off frequenc* of t!e filter is a ('1& J " 711> J
c $'&& J d (>#7 J Ans:B
[8] A net.or desi%ned to pass si%nals at frequencies a"o+e a specified cut?off frequenc* is called a a lo.?pass filter " !i%!?pass filter c "and?pass filter d "and?stop filter Ans: B
[7] A net.or desi%ned to pass si%nals at frequencies "elo. a specified cut?off frequenc* is called a a lo.?pass filter " !i%!?pass filter c "and?pass filter d "and?stop filter Ans: A
[>] A net.or desi%ned to pass si%nals .it! frequencies "et.een t.o specified cut? off frequencies is called a a lo.?pass filter " !i%!?pass filter c "and?pass filter d "and?stop filter Ans: C
/!e follo.in% refers to questions 9 and 1' A filter section is to !a+e a nominal impedance of 8(' and a cut?off frequenc* of ( J [9] A lo.?pass /?connected s*mmetrical filter section is comprised of a 9>8> O in eac! series arm, 1(># p) in s!unt arm " #9&# O in eac! series arm, ($87 p) in s!unt arm c 9>8> O in eac! series arm, ($87 p) in s!unt arm d #9&# O in eac! series arm, 1(># p) in s!unt arm
Ans: B
[1'] A lo.?pass π?connected s*mmetrical filter section is comprised of a 9>8> O in eac! series arm, 1(># p) in s!unt arm " #9&# O in eac! series arm, ($87 p) in s!unt arm c 9>8> O in eac! series arm, ($87 p) in s!unt arm d #9&# O in eac! series arm, 1(># p) in s!unt arm Ans: A ELECTRONICS DEVICES OBJECTIVE TYPE QUESTIONS
[1] A Zener diode is used for a) Voltage Regulation b) Rectification c) Noise Suppression d) Blocking A.C Ans: Voltage Regulation
[2] An SCR is a device having a) Three layers with four junctions b) Three layers with two junctions c) Four layers with three junctions d) Two layers with three junctions Ans: Four layers with three junctions
[3] An amplifier has a gain of 10,000 expressed in decibels the gain is a) 10 b) 40 c) 80 d) 100 Ans: 80
[4] An emitter follows has a) High input impedance and high output impedance. b) High input impedance and low output impedance. c) Low input impedance and high output impedance. d) Low input impedance and low output impedance. Ans:High input impedance and low output impedance.
[5] Semi-conductor diode time constant is equal to
a) The value of majority carrier life time b) The life time of minority carrier c) The diffusion capacitance time constant d) Zero Ans: The value of majority carrier life time
[6] To prepare a P type semiconducting material the impurities to be added to silicon are a) Boron, Gallium b) Arsenic, Antimony c) Gallium, Phosphorous d) Gallium, Arsenic Ans:Boron, Gallium
[7] FET is a good signal chopper because a) It exhibits no offset voltage at zero drain current b) It occupies less space in integrated form c) It is less noisy d) It has got high input impedance Ans: It exhibits no offset voltage at zero drain current
[8] In Bipolar Junction transistors, the type of configuration which will give both voltage gain and current gain is a) CC b) CB c) CE d) None Ans: CE
[9] To increase the input resistance and decrease the output resistance in negative feedback, the type used is a) Voltage Shunt b) Current Series c) Voltage Series d) Current Shunt Ans: Voltage Series
[10] A series capacitance used in a filter circuit represents
a) Low-Pass b) Band-Pass c) High-Pass d) None Ans: High-Pass [11] An ideal power supply is characterized by a) Very large output resistance b) Very small output resistance c) Zero internal resistance d) Infinite internal resistance Ans: C
[12] An ideal diode should have a) Zero resistance in the forward bias as well as reverse bias b) Zero resistance in the forward bias and an infinitely large resistance in reverse bias c) Infinitely large resistance in reverse bias d) Infinitely large resistance in forward as well as reverse bias Ans: B
[13] One coulomb-per-second is equal to one: a) Watt b) Joule c) Volt d) Ampere Ans:D
[14] Which of the following is one of the functions performed by a diode? a) Filter b) Amplifier c) Rectifier d) Inverter Ans: C
[15] What is the “power factor”? a) Ratio of true power to apparent power b) Peak power times 0.707 c) Sin of the phase difference between E and I d) Cos of the phase angle between true power and apparent power
Ans:A
CH/H 4P4/ 4H3D CHF/I/I3
[1] An open loop s*stem represented "* t!e transfer function Gs s?1 2 sQ( sQ& is a 4ta"le and of t!e minimum p!ase t*pe " 4ta"le and of t!e non?minimum p!ase t*pe c Lnsta"le and of t!e minimum p!ase t*pe d Lnsta"le and of t!e non?minimum p!ase t*pe Ans:B
[(] /!e open loop transfer function Gs of a unit* feed"ac control s*stem is %i+en as, Gs [ sQ(2& 2 s(sQ( ] )rom t!e root locus, it can "e inferred t!at .!en tends to positi+e infinit*, a /!ree roots .it! nearl* equal real parts eKist on t!e left !alf of t!e s?plane " Hne real root is found on t!e ri%!t !alf of t!e s?plane c /!e root loci cross t!e 0R aKis for a finite +alue of - S' d /!ree real roots are found on t!e ri%!t !alf of t!e s?plane Ans:A
[&] Gi+en t!at
t!en t!e +alue of A & is [GA/('1(] a 1$AQ1(I " 19AQ&'I c 17AQ1$I d 17AQ(1I Ans:B
[$] /!e input Kt of a s*stem are related as *t T t?U KVcos&VdV /!e s*stem is [GA/('1(] a /ime?in+ariant and sta"le " 4ta"le and not time?in+ariant c /ime?in+ariant and not sta"le d ot time?in+ariant and not sta"le Ans: B
[8]/!e feed"ac s*stem s!o.n "elo. oscillates at ( rad2s .!en [GA/('1(]
a ( and a'7$ " & and a'7$ c # and a'$ d ( and a'$ Ans: A
[7] /!e )ourier transform of a si%nal !t is 0R (cosRsin(R2R /!e +alue of !' is [GA/('1(] a 12# " 12( c 1 d ( Ans: C
[>] /!e state +aria"le description of an /I s*stem is %i+en "*
.!ere * is t!e output and u is t!e input/!e s*stem is controlla"le for, [GA/('1(]
a a1S',a(',a&S' " a1',a(',a&S' c a1',a(',a&' d a1S',a(S',a&' Ans:D
[9] /!e state transition dia%ram for t!e lo%ic circuit s!o.n is [GA/('1(]
Ans: D
[1'] Gi+en t!at
t!en t!e +alue of A & is [GA/('1(] a 1$AQ1(I " 19AQ&'I c 17AQ1$I d 17AQ(1I Ans: B
[11] /!e differentiator !as a transfer function .!ose [Gate 1997] a F!ase increases linearl* .it! frequenc* " Amplitude remains constant
c Amplitude increases linearl* .it! frequenc* d Amplitude decreases linearl* .it! frequenc* Ans: A
[1(] Introduction of inte%ral action in t!e for.ard pat! of a unit* feed"ac s*stem results in a [Gate 1997] a ar%inall* sta"le s*stem " 4*stem .it! no stead* state error c 4*stem .it! increase sta"ilit* mar%in d 4*stem .it! "etter speed of response Ans: A
Di)it&l Electronics objectie Q!estions# P&rt * [1] It is required to construct a counter to count upto 100(decimal). The minimum number of flipflops required to construct the counter is a) 8 b) 7 c) 6 d) 5
Ans:A [2] The gate that assumes the 1 state, if and only if the input does not take a 1 state is called........ a) AND gate b) NOT gate c) NOR gate d) Both b and c
Ans: D
[3] For NOR circuit SR flip flop the not allowed condition is.... a) S=0, R=0 b) S=0, R=1 c) S=1, R=1 d) S=1, R=0
Ans: C Wh!n S"R"# $h! %&$'&$ is s&()!*$ $% &n'+!,i*$a(! (!ha.i%&+ /h!n S an, R +!$&+n $% 0 si&$an!%&s1
[4] A bistable multivibrator is a a) Free running oscillator b) Triggered oscillator c) Saw tooth wave generator d) Crystal oscillator
Ans: B
[5] For a large values of |VDS|, a FET behave as a) Voltage controlled resistor b) Current controlled current source c) Voltage controlled current source d) Current controlled resistor
Ans: C
[6] When a step input is given to an op-amp integrator, the output will be a) a ramp b) a sinusoidal wave c) a rectangular wave d) a triangular wave with dc bias
Ans: A
[7] In a full-wave rectifier without filter, the ripple factor is a) 0.482 b) 1.21 c) 1.79 d) 2.05
Ans: A
[8] Hysteresis is desirable in Schmitt-trigger, because a) Energy is to be stored/discharged in parasitic capacitance b) Effects of temperature would be compensated c) Devices in the circuit should be allowed time for saturation and desaturation d) It would prevent noise from causing false triggering
Ans:C
[9] For a 10-bit DAC, the Resolution is defined by which of the following a) 1024 b) 1/1024 c) 10 d) None
Ans:B
[10] SRAM full form is a) Serial Read Access Memory b) Static Random Access Memory c) Static Read-only Access memory
Ans: B
[11] What are the minimum number of 2 to 1 multiplexers required to generate a 2 input AND gate and a 2 input Ex-OR gate? a) 1 and 2 b) 1 and 3 c) 1 and 1 d) 2 and 2
Ans:A
[12]The output of a logic gate is ‘1’ when all its inputs are at logic ‘0’. Then gate is either a) A NAND or an EX-OR gate b) A NOR or an EX-NOR gate c) An OR or a EX-NOR gate d) An AND or an Ex-OR gate
Ans: B
[13] A PLA can be used a) As a microprocessor b) As a dynamic memory
