engg services electrical engineering objective paper 2 2011

8/19/2019 Engg Services Electrical Engineering Objective Paper 2 2011

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IDO NOT OPEN THIS TEST BOOKLET UNTIL YOU ARE ASKED TO DO SO)

T B C : P-RSR-L.,.RRB Test Booklet Series

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61

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[ DO NOT OPEN THIS TEST BOOKLET UNTIL YOU ARE ASKED TO DO SO


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I. The appli.:d voltage of a ccrtain transformer

IS incn:as"d by 75%; while thc frcqucncy of

the appli"d voltage is reduccd by 25%. I hI

maxImum con: flux density will '

la) Increase by scven times

(b) Incrcase by three times(c) Rcduce to onc quarter

(d) Rcmam thc same

2. A 10 kVA. 1500 / 250 singlc phasc

transformer has the following results :- . -, ,

0 ( 1cst . 2:;0 volts 0·8 amps ' 50 W> ~ . .

S .C rcst 60 volts 3 amps . 45 W '_ . _ . : _ _ _ _ _ :. . •

Then eflicicncy at half fuJI load at 0 ·8 powerfactor will be :

(a) 98·49%

b) c}7'o8 (e) 98 ·28 %

(d; 9 · 8 "

3. A 4 k VA. 400 V 200 V single phase

tr.msformer has resistance of 0·02 pu and

reactan"e of 000 pu. The resistanc" and

reactance rderr"d to high voltagc , ide an: :

(a) 0 ·2 n dlld 0·6 n(h) 0 ·812 itnd 2 ·4 n(e) 0 ·08 U and 0·24 n(d) 1 U and J n

4 . '1hc full-load coppcr-Ioss and iron-loss of a

transforml;;r an: 6400 Wa n d 500 W,ro;;spcctivcly . 'I hc abow coppcr loss and iron

loss at half load will be :(a) noo W and 250 W respectively(b) l:'OO W and 500 W n:sp"ctlvely

i C) 1600 Wand 125 W n:spcctive y

\ d) 1600 V and 500 W rcspcctiveJ)

5. In a transformcr, o.:ro voltage regulanon attullioad is :

(a) Not possible

(b) Possible at cading power factor load

(c) Possible at lagging power lactor load

(d) Possible at UOlty power facto load

6 . A two-winding 220 V d 10 V 1 5 kYAtransformer is reconnected ~ a 2201330 Vautotransformer . It IS re-rated as .(a) 3-88 kYA

(b) 4·488 kVA

(c) I 58 kYA

(d) 2258 kVA

7 . A 2 Vii V two-wmding transformcr is

connected as an autotransformer . [ b voltageregulation as an aUlUtransforrm:r comparo;;dto the two-windmg transformer is

(a) The same

(b) 1·5 times

(c) 2 times

(d) 3 times

8. When one transformer IS removed from aL \ bank o f 30 k VA transformer. the

capacity oflhe resulting 3-phasc transformerin V-V connection" III be .(a) 11 ·5kVA

(b) J 7·3 kVA

(c) 20 kYA

(d) 25 ·9 kVA

9. Which three-phase connl;;ction can bc usedin a transforml'f to introduc" d phasediffcT


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10 . Conditions for parallel operation oftransformers are :I. The same voltage ratio2. The same per unit irnpedance3. The same polarity4. The same phase sequence5. The relative phase displacementWhich are the absolutely essentialconditions?(a) \ ,2 , 3, 4 and 5(b) 2,3 and 4(c) 3, 4 and 5(d) 1 , 2 and 3

II. The emf induced in a conductor of machine

driven at 600 rpm, the peak value of fluxdensity is 1 ·0 Wb m , diameter of machine.2 ·0 meter and length of machine 0·30 m is :(a) 41 ·83Vb) 29·58 V

(c) 9-42 V(d) 18·84 V

12. A 440 V , 3-phase, J O pole and 50 HzsynchrOhous motor delivering a torque of

50- Nm, delivers a power of :1t

a) 50 W(b) 500 W(c) 1000 W(d) 2000 W

13. The ·maximum efficiency occurs in aseparately excited de generator when theterminal voltage is 220 V and the induced

emfis 240 V the stray losses, if he armatureresistance is O 2 n, will be :(a) 1000 W(b) 2000W(c) 3000 W(d) 4000 W

14. An eight pole de generator has a simplewave wound armature · containing 32 coilsof 6 turns each. Its flux per pole is 0 ·06 Wb.The machine is running at 250 rpm. Theinduced armature voltage is :(a) 96 V(b) 192 V(c) 384 V(d) 768 V

15. How many segments will be there for thecommutator of a 6-pole dc machine havinga simple wave-wound armature with72 slots?(a) 73

(b) 72

(c) 71

(d) 70

16. Which one of the following staternents iscorrect for the ideal field ·excitation duringstarting in case of shunt and compoundmotors?

(a) Maximum, because motor torquerequired to overcome friction and loadtorque.

.(b) Maximum, because voltage should bebuilt slowly .

(c) Maximum, because small excitationwill lead to low operating speed duringstarting.

(d) It can .be anything because it does notmatter in case of these motors

17. A turbine-generator set has a regulationconstant .of 6 on the generator rating of

120 MVA 50 Hz. The generator frequencydecreases by 0·01 Hz. The increase inturbine output for steady-state operation is :(a) 0·8 MWb) 0·4 MWc) 0 ·2 MW

(d) 40 MW

(Contd.)


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18. With reference to hydropower station, thegraphical representation of the discharge asa function of time is known as :(a) Monograph(b) Hectograph(c) Load dumtion curve(d) Hydrograph

19, One million cubic meters of water is storedin a reservoir feeding a water turbine. Thedensity of water is 993 kg/m> , If the c.:ntr.:of mlllSS of water is 50 meters above theturbine and the losses are negligible, theenergy produced by that volum.: ofwat r is :(a) 135 ' J MWhr(b) 130 MWhr(c) 120 MWbr(d) 140 MWbr

20. For ham ss ing low variable water heads , thesuitable hydraulic turbine with reaction andadjustabh: vanes runners isa) f'rdllles

(b I Impeller(c) Kapland) Pelton

21. In a thermal power station, a typical heatbalan\:< sheet, for a large turbine and surfacecondenser taken together, is the percentagedistribution of heat energy in :1 Work done or thermal efficiency2 Fri.:tion and windage loss3. Heat to circulating water4, Heat in condensate to e retained to

:h.: boiler .Th.: percentage amount of heat in the headsstated above. in the descending order is '(a) 3,4, I and 2(bl 2, 1 . 4 and 3(c) 3, 1. 4 and 2(d) 2,4, I and 3

(4)

22. The incremental cost characteristics of twogenerators ddivering a load of200 MW areas follows

dF_ 2'0+0'0IP.dP.dF

~ 1·6 + 0·02PdP 1

2For economic operation the generators P,and P should e(a) 120 MW and 80 MW(b) 80 MW and 120 MW(c) 120 MW and 120 MW(d) 80 MW and 80 MW

23, The radiation shield for a nuclear powerreactor for biological safety is prov ided byhaving the reactor:(a) Immer.red in water pool(b) Encased by thick. metal walls(c) Encased by thick concrete wall(d) Isolated from outside world with strong

magnetic fields24. A Pumped storage hydro-electric plant'

consists of :(a) A synchronous machine and a multi

stage centrifugal pump in one shaft(b) A synchronous machine, a reaction

turbine. and a multistage centrifugal

pump all in one shaft(c) An induction generator, a synchronous

machine and a reaction turbine, all inone shaft

(d) An induction generator, a synchronousmachine, and a multistagt: centrifugalpump, all in one shaft

25. The economics of power plant is greatlyinfluenced by :I , Load factor

2. Utilimtion factor3. Unit capacity4. Type ofload(a) 1,2, 3 and 4(b) I ,3and4(e) 1,2and3(d) 2 ,3and4

(Contd.)


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26. Match List-I with List-II and select the

correct answer using the code given be low

the lists:

List / List / I

A . Thyrite arrester I. Tower location

B Sag template 2 Cross bondingC. Cable sheaths 3. Restriking voltage

D. Circuit breaker 4. Non-linear resistorCode

A B(a) 3 I

(b) 4 1

C D2 42 3

(c) 3 2 4

(d) 4 2 327. The line currents of a 3-phase power supply

are:

IR = 3 + j5 AIy = 2 + j2 AI = -2 - j I A

The zero sequence current wi II be :

(a) I + j2 A

(b) 5 + j7 A(c) I + j4 Ad) 2 - l A

28. The incremental fuel costs for two

generating units G, and G, are given by :

Ie, = 25 + 0·2 PG, and Ie , = 32 + 0·2 PG,where PG, and PG, are real powers

generated by the units. The economic

allocation for a total load of 250 MW,

neglecting transmission loss, is given by

(a) PG, = 142·5 MW and PG, = 107 ·5 MW

(b) PG, = 109·75 MW andPG,= 140 25MW

(c) PG, = 125 MW and PG, = 125 MW

(d) PG, = 100 MW and PG, = 150 MW

29 . The main objective of load frequencycontroller is to apply control of :(a) Frequency alone(b) Frequency and at the same time of real

power exchange via the outgoing lines(c) Frequency and at the same time of

reactive power exchange via the

outgoing lines(d) Frequency and bus voltages30 . The m ain objectives of load frequency

control in a power system are :1 To bring the steady state error to zero

after load change2. To maintain the net tie-line flow3. To maintain voltages on all buses4. To economize the cost of generation(a) 1 and 2(b) 2 and 3(c) 3 and 4(d) 1 , 2.3 and 4

31 . The current of a single phase load drawnfrom a 3-phase system , has :(a) Zero sequence component of current

as zero(b) Negative sequence component of

current more than positive sequencecomponent

(c) Positive, negative and zero sequencecomponents equal

(d) Negative sequence component of current

less than positive sequence component32 . T h e Equal area criterion for the deter

mination of ransient stability of the synchronous machine connected to an infinite bus:(a) Ignores line as well as synchronous ma-

chine resistances and shunt capacitances(b) Assumes accelerating power acting on

the rotor as constant(c) Ignores the effect of voltage regulator

and governor but considcrs the inherentdamping present in the machine

(d) Takes into consideration the possibilityof machine loosing synchronism afterit has survived during the first swing.

33 . If the inertia constant H = 8 MJIMVA for a50 MVA generator, the stored energy is :(a) 50 MJ(b) 8 MJ(c) 400 MJ(d) 6·25 MJ

(Contd.)


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34 . Match ist-I \ \ i th List-II and se iect thecorn:ct ans\\er using th.: cod.: g ivl.:n bl.:lowthe lists .

35

36 .

LiST-

A . Mho rday

B. Plain Impl.:- 2.danet: fday

C . Dirc:ct ional 3rday

D . Angle imp 4

da nce rday

·od.

A B ((a) 3 2(b) 4 2(e) 3 2(d) 4 2

D434.3

In an HV DC syst.:m .

s T I I

X

x

.

x ·

R

R

R

(a) Both gt:n.:ratlOn and distribution an: de(b) Oener-ation is ae and distribution is de(e) Genc:ration is de and distribution is ae(d) Both gen.:ration and distribution an: ae

Dark current 10 a st'miconductor photodiode is .(a) The: forward bias current(bl Th forward saturation current(e) 'Ib r"verse saturation current(d) Th transient current

37 . Compared to the bipolar Jun c:t\on transistor.a JFFT ;I. Has a larg"r ga in bandwidth produ -2. [s less noisy~ Has "ss input n ~ s t n c e4 . Has eum:nt flow dut: to only majority

carriers

a) 1.2 . dnd 4 are , •. . , ,, ,(b) I and 2 are corn:ct(e) 2 and 4 are corr ect(d) 3 and 4 are correct

38. An emitter follower reguhllor ha s thefoltow ing disadvantage(a) It do s not provide high ~ ai n(b) No provision xist , for _aryin g the

output voltage(e) Its output resi s ta nce is h r (d) It cannot withstand h igh load current

39 Considc:r the fo)[owing , tat.:ments :

40 .

41.

42 .

I . A Lenc:r diode deg;r-


7/20

43. Which one of the following is NOT true ofdirect coupled amplifiers?

44.

a) Low costb) Can amplify high frequency signalsc) Can amplify low frequency signalsd) Operating point shifts with temperature

variations

Rr

RV ~ N V - - - _ - - j

45.

. - - - - - l

R ,

The circuit shown is :

a) A low pass filter

b) A clamper

c) A lag compensated inverting amplifier

d) A narrow band video amplifier

R

e

The circuit shown is :a ~ A low pass filterb) A high pass filterc) A comparatord) An all-pass filter

R

OA

46. One shot multi-vibrator, with a pulse inputgives an output:

a) A single triangular pulse

b) A square pulse

c) An impulse

d) A single sinusoid pulse

47 . .

48.

A . . - - - -4B . 1

C 1 1 _/x

For logic circuit shown, the required inputsA B and C to make the output X I are,respectively,

a) 1, 0andl

b) 0 , 0 and I

c) l , l n d l

d) 0 , 1 and I

The Boolean expression for the shaded areain the Venn diagram shown is :

a) A B C

b) AB ABC

e) ABC ABC

d) AB ABC

Contd.)


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49. Consider the following statements.

The h-parameters of a BJT :

I

2.

Represeni the input resi stance , outputconductance , current gain etc

Can be easily measured n the

laboratory

3. Can be used in circuit analysis over awide range of freq uencies

4. Constitute a simple small signal modelfor easy circuit analysis at low frequencies where junc tion capacitancescan be neglected .

Which of these statements are correct?

(a) I, 2, 3 and 4

(b) 1 ,2and4

(c) 1 3 and 4

(d) 2,3 and 4

50. Consider the following statements :

1. Amplitude distortion arises due todifferent frequency components being

amplified differently2. White noise gives the same noise per

unit bandwidth across the entirefrequency spectrum

3. If an amplifier has two poles such thatp, = 4p then the dominant pole is p,

4. The self-biasing emitter resistance ofan amplifier is bypassed by a largecapacitance to reduce degeneration at

higher frequenciesWhich of these statements are correct?

(a) 1 , 2 , 3 and 4

(b) 2 and 4

. (c) 2 and 3

(d) 3 and 4

51. R.

v, ,,--In the given circuit , the magnitude of the

output voltage

IV.I = 3V 1 + 2V, 7V 3 ,then the valuesof Rl R R, and R. are:

(a) 3 kQ, 2 kQ, 7 H l and I l l

(b) Q , i kQ, .72 kQ and 12 kQ

(c) 4 kQ , 6 kQ, 1f kQ and 12 kQ

(d) t kQ, -t6 kQ, kQ and 12 kQ

52 . A scmiconductor ROM is preferred to asemiconductor RAM because:

(a) ROM is cheaper than RAM

(b) ROM is faster

(c) ROM does not rcquire power supplyfor their operation

(d) Program stored in the ROM cannot bealtered

53. The first machine cycle ofan instruction isalways:

(a) A mcmory read cycle

(b) A fetch cycle

(c) An 1 0 read cycle

Cd) A memory write cyc.le

(Contd.)


9/20

i.

54. If the status of the control lines SI and SO is

LOW then 8085 microprocessor IS

performing :

a) Reset operation

b) HOLD operation

c) Hah operationd) Interrupt acknowledge

55. The output data lines of micro processors and

memories are usually tristated because:

a) More than one device can transmit

information over the data nus by

enabling only onc device at a time

b) More than onc device can transmit overthe data bus at the same time

c) The data lines can bc multiplexed for

both input and output

d) It increases the speed of data transfers

over the data bus

56 . AND operation of 79)\O and --S6) \orcsults in :

a) 50 H

b) 48 H

c) 42 H

d) 08 H

57. ALU Arithmetic Logic Unit) of an 8085

microproccssor consists of:

a) Accumulator temporary register

arithmctic and logic circuits

b) Accumulator, arithmetic , logic circuits

and five flags

c) Acc\U1lulator, arithmetic and logic circuits

d) AccumulatoT temporary register ,

aritiunetic, logic circuits and five flags

58 . The description of a program counter PC)

in 808S microprocessor is :

a) An up/down counter

b) An 8-bit registerc) Initialized automatically by micro-

processord) Used to point to stack memory area

59 . Which components are NOT found on chip

in a microprocessor but may be found on

chip in a microcontrolJer ?a) SRAM and USART

b) EPROM and PORTSc) EPROM, USART and PORTS

d) SRAM , EPROM and PORTS

60. Which value a program counter will hav.ewhen non mask able interrupt of 8085

microprocesor is serviced?

a) 0004 H

b) 0014 H

c) 0024 Hd) 0034 H

61. For the purpose of data processing an

efficient assembly language programmermakes use of the general purpose registers

rather than memory. The reason is :a) The set of instructions for data

processing with memory is limited(b) Data processing becomes easier when

registers are usedc) More memory related instructions are

required in the program for data

processingd) Data processing with registers takes

fewer cycles than that with memory

Comd.)


10/20

62 . 'N'hil.: a program is being executed in anIntel 8085 microprocessor. th.: programcounter of the microproc.:ssor containsa) The memory address ofthe instnlction

that is being currently executed

(b) The memory address of the instmction

that is to be executed next( , ) The number of mstructions that have

aln:ady been executed

(d) Ihe total number ofmstructions in thecurrent program still to be executed

63 . Which one of the following statements is~ r correct 'a) C\IP A is a single b)1e instmct ion and

C:>vIA is not an instruction

(b) The instmction SL 'B 1\ sets the ~ r o

flag(e) Bus is a group o f wires(d) Lnstruction rNR C does not affect carry

flag

64 (0 "x.ocute the following instructionsIiI LOA 2 100 II[ill LXIH.2100H

by an Intel 8085 microprocessor the

numbers of mt:mory cycles required liTe :

a) 2 for l i l and] for Iii](b) 4 for tiJ and 2 for [til(.:) 1 lor [i ] and 3 tor Iii](d) 4 [or [i l and ] for Iii]

65 . In 8085 microprocessor. during PUS I VPSWop ·ration. stack pomter is :(a) D.ocrement.:d by one(b) lJecremt:nteJ by two

( , ) Incremented by one(d) Incremented by two

r v.

66 .

The logic circuit used to generate the actiVl

low chip select signal CS) by an Intel 8085

microprocessor to address a peripheral is

shown in the figun: . The peripheral will

respond to address in the range :

(a) 7800 H . 7 H F Ii

(b) 1000 H I H I- i

(c) 8000 i 8 t H

(d) 8800 H · 8 FH-

67 . The 8259 A programmable Interrupt

controlkr can

I . Manage eight interrupts

2 . Vector an interrupt request anywhen:

in memory map

3 Have 8-bit or 16 b it interval between

interrupt vector locations

4 Initialized with op


11/20,

68. To address the full memory space of an Intel

8085 microprocessor four RAMS o f

different sizes are available :

I SK x 8

2 . 16K x 4

3 32 K x 44 . 32 K x 16

What minimal combination of chip(s) will

serve the purpose?

(a) 1 , 2, 3 and 4

(b) 2

e) 3

(d) 4

69. For which of the following systems, the

signal to noise ratio is the highest?

(a) PAM

(b) PWM

c) PPM

(d) PAM and PWM

70 . An indirect way of generating FM, is :

(a) The Armstrong modulator

(b) The reactance FET modulator

(c) The varactor diode modulator

(d) The reactance bipolar transis tor

modulator

71. Diode demodulator will ignore :

(a) The amplitude modulation

(b) The frequency modulation

(e) PCM

(d) PWM

72 . Match List-I with List-II and select thecorrect answer using the code given belowthe lists:

Lisl 1

A. Phase locked loopB. Super-heterodyne

receiverC. FM receiverD. Envelope detectorC o d e

B C Da) 4 1 2 3

(b) 3 2 4c) 4 2 3d) 3 2 4

Lis/ II

I. Mixer2 . De -emphasis

filter3 . Diodes4 . VCO

73 . Quantizing noise occurs in :

(a) Pulse width modulation

b) Frcqucncy division mutiplexing

(e) Pulse code modulation

(d) Time division multiplexing

74 . If ACF denotes the autocorrelation functionand PSD denotes the power spectral density ,

then for white noise , A CF is :(a) A Gaussian while PSD is uniform

(b) A delta function while PSD is uniform

(c) A delta function while PSD ISexponential

(d) An exponentia l while PSD is uniform

75. The demodulation of a delta modulated

signal is achieved by :(a) Integration

(b) Differentiation

(c) Sampling

(d) Band pass filtering

(Contd.)


12/20

76. In phase modulation, phase deviation isproportional to :

(a) Carrier amplitude

(b) Carrier phase

(c) Message signal

(d) Message signal frequencies

77. In differential PCM, each word indicates:

(a) Difference between a sampleamplitude and a reference signal

(b) Difference in amplitude between asample and the previous sample

(c) Addition of a sample amplitude and areference signal

(d) Addition of amplitude ofa sample andthe previolls sample

78. PPM signal is :

(a) Differentiation of PWM

(b) . Integration ofPWM

(e) Differentiation of PAM

(d) Not related to PWM or PAM

79. The main advantage of pre-emphasis circuitin FM transmitter is :

(a) To increase the carrier power

(b) To improve the signal to noise ratio atlow audio freqllencies

(c) To increase the bandwidth of side band

(d) To improve the signal 10 noise ratio athigh audio frequencies

@

80 . The highest frequency stability is achievedby using an oscillator of the type:(a) Colpitts(b) Crystal controlled(c) Hartley(d) RC oscillator

81. An aerial having a directivity of 90 isoperating at a wavelength of 2 m. Themaximum e fTective aperture of he aerial is :(a) 7·16 m(b) 14·32 m (c) 28·64 m (d) 57·28 m

82 . MSK (Minimum Shift Keying) is anorthogonal FSK scheme that gets its name ·from the fact that :(a) The phase shin is minimum(b) The error probability is minimum(cl The transmission power required is

mmlmum(d) The transmission bandwidth required

IS nlll11mUm

83 . In high . speed TD M , the channels areseparated in the recei vcr employing:(a) OR gate(b) NAND gate(c) NOR gate(d) AND gate

84. Which of the following component blocks

is NOT requiredin

the FDM transmiuerblock diagram?(a) Filter culling off lower and higher

frequencies(b) Filter cutting olfhigher frequencies(c) Single side band modulator(d) Double side band modulator

(Contd.)


13/20

85. An SCR is in conducting state, a r v rs 88 . A structure obtained by lightly doped n - driftvoltage is applied between anode and region between the layers of a pn junction acathode , but it fails to tum off. What could PIN diode is obtained . This structure isbe the reason? effective in :

a) Positive voltage is applied to the gate. a) Making the diode support large reverse

b) The reverse voltage is small.blocking voltages

b) Making reverse recovery process slowc) The anode current is more than the c) Making the diode have high on-stateholding current. voltage drop

d) Tum off time ofSCR is large. d) Reducing the voltage spike during tumoff due to stray inductance

86 . A reverse conducting thyristor RCT)Which one of the following statements isnormally replaces: 89 .NOT correct for a MOSFET ?

a) A pair of anti-parallel thyristors in a a) Are easy to parallel for higher currentcircuit

b) Leakage current is relatively highb) A combination of a thyristor and an c) Have more linear characteristic

anti-parallel diode in a circuitd) Overload and peak current handling

c) A thyristor in a situation where it is not capability are highrequired to have reversed blockingcapability at all 90 . In a GTO, anode current begins to fall when

d) Conventional conversIOn grade the gate current :

thyristors having large tum off time a) Is negative peak at time t = 0b) Is negative peak at t = storage period t

87 . A thyristor can be switched from a non- c) Just begins to become negative at t =0

conducting state to a conducting state by d) Just begins to become positive at t = 0applying :91. Consider the following statements :

I Voltage mor than forward break overI A thyristor requires tum ofT circuitvoltage

while transistor does not.dv 2 The voltage drop of a thyristor is less2. A voltage with high dt

than that of a transistor .3 Positive gate current with positive 3 A thyristor requires a continuous gate

anode voltage current.

4 . Negative gate current with positive 4 A transistor draws continuous baseanode voltage current.

a) I, 2, 3 and 4 are correct Which of these statements are correct?

b) I, 2 and 4 are correcta) 1,2 , 3 and 4b) 1 and 2

c) 1, 2 and 3 are correct c) 2 WId 4d) 2, 3 WId 4 are correct d) 1 and 4

Contd.)


14/20

92. A field effect transistor with an anti-paralh:1body diode blocks :(a) Bidirectional voltage and passes

unidirectional curr.:nt(b) Bidin:ctional voltage and passes

bidirectional current

(el L nidireetional voltage and passesunidirt ,ctional current(d) Lnidireetional voltage and passes

bidirectional current

93. For low-spet:d high-power reversiblt:operation, the most suitable drives are:(a I Voltage sourc.: inverter bed ac drives(b) Current source inverter bed ae drives(e) Dual com-erter bed de drives

(d) Cycloconvt:rter bed ac drives

94 . An advantage of a eycloconverter is :(a) Very good power factor(b) Rcquires few number of thy ristors(c) Commuta tion failur.: does not short

circuit the source(d) Load commutation is possible

95. In de choppers, the waveforms for input and

output voltages are respectively:(a) Discontinuous and continuous

(b) Both .:ontinuous(c) Both discontinuous(d) Continuous and discontinuous

96. The use of multi phase rectifier in place of1 -phast: rectifIer results in ;(a) Increased output voltage and reduc.:d

harmonics

(b) Increased output voltage and increasedharmonics

(c) Decreased output voltage and reducedharmonics

(d) Increased output voltage and no effecton harmonics

97. In a 3-phase semi-converter, for firing angleless than or equal to 60°, freewheeling diodeconducts for :

(a) 90°

(b) 60°

(c) 30°Cd) 0

98. What is the waveform o f the currentflowing through the diode in a buck-boostconverter?

(a) Square wave

(b) Triangular wave

(c) rrapewidal wave

(d) Sinusoidal wave

99. n order to simpliry the designofa convertertransformer, the two converters in a dualconverter should be conn.:cted using :

(a) Series conm ,ction

(b) Cross connection

(c) Direct anti -paralld connection

(d) Anti-parallel connection

100. An integral cycle ae voltage controller isfeeding a purely rt:sist ive circuit from asinglc phase ac voltage source. The currentwaveform consIsts alternately burst o fN-complete cyck of conduction followedby M-complete C)'cles of e tinction. The rmsvalue of the load voltage equals the rmsvalue of the supply voltage for:

(a) \ I - M

(b)

(c) , = M ' 0

Cd)

(Contd.)


15/20

irections

Each of the next Twenty (20) items consistsof two statements, one labeled as theAssertion ( A r and the other as Reason

(R) . You are to examine these twostatements carefully and select the answersto these items using the codes given below:Codes

(a) Both A and R are individuallytrue and R is the correct explanationof

(b) Both A and R are individually truebut R is N O T the correct explanationof A

(c) A is true but R is false(d) A is false but R is true

101. Assertion (A) [n a certain case, a deshunt generator failed tobuild up the voltage.

Reason (R) Shunt field resistance ofa de shunt generatorshould be more than itscritical field resistancevalue to generate voltage:

102. Assertion (A) While running on lightload a salient polesynchronous machine cancontinue to operate oninfinite bus-bars even ifits excitation fails.

Reason (R) A salient pole machinedevelops reluctance

power due to the variablerei uctance offered by thesalient poles.

103. Assertion (A) A squirrel cage induction

motor is preferred to the

slip ring induction motor.

Reason (R) Higher starting torque is

the main consideration.

[04. Assertion (A) [f two transformers with

Reason (R)

Xdifferent R ratios are

operated in parallel, one

of the transformers

becomes overheated

.when full KVA output is

drawn from them.

The impedance triangles

are not identical in shape

when two transformers

having different voltage

ratings are operated in

parallel.

105. Assertion (A) In a certain case of load

change, an alternator

became unstable and

pulled-out.

Reason (R) [n an alternator, damper

winding is present.

106. Assertion (A) t is not necessarily

desirable to compensate

by a series capacitance

for all the line reactance.

Reason (R) Power can be trans-

formed only i f reactance

is present.

(Contd.)


16/20

107. Assertion (A) The collector current ina BJT in common basemode increases slightly

~ t hincrease in collectorbase voltage.

Reason R) Increased collector-basebias causes avalanchebreakdown to increasethe current.

108. Assertion A) In a p-type semiconductor, with increasein the level of doping ata fixed temperature, thehole concentrat ionincreases but the electronconcentration falls .

Reason (R) Law of mass action holdsgood in case of semiconductors.

109. Assertion A) For class A operation ofCE transistor amplifier , theoperating point cannot befixed near VCE = 0 point.

Reason (R) During the positive halfof the input cycle , thetransistor may be drivenfrom active region tosaturation region, thus

loosing the class A waveshape in the output.

110 . Assertion (A)

Reason (R)

•

If the output voltagewaveform in a transistoramplifier is a true replicaof the input waveform.then i t is said to be

operated in class A mode .The Q point cannot befixed near Ic = O.The positive half cycle ofthe input will be clippedoff in the output due totransistor being driven intocut-off from active region .

I II. Assertion A) At OOK , a semiconductorbehaves as an insulator.

Reason R) No free carriers are available in ·the semiconductorat OOK

112. Assertion (A) In a full-wave rectifier, itis absolutely necessary touse identical diodes havingidentical characteristics .

Reason R) In pract ice, it is neverpossible to have two

diodes having identicalcharacteristics due to

technological limitations.

113. Assertion A) The operating point in atransistor amplifier shiftswith changes in temperature .

Reason R) Reverse saturationcurrent approximately

doubles for every 10°Cincrease in temperature

114. Assertion A) In the work functionmodel of Schottky barrierdiode contacts to n-typesemiconductor, the metalwork function will be

highcr than the semi

conduc tor work function.

Reason R) To equalize the Fermi

levels on the ferro sidesof the contact, electronsfrom semiconductor surfucemove to metal side fonninga space charge region athe semiconductor surface.

Contd.)


17/20

115. Assertion A) The energy band diagram

of a real semiconductor

cannot e represented by

flat conduction and

valence bands.

Reason R) The presence of energystates in the forbidden

energy gap results in

carrier trapping, giving

rise to finite curvature in

the bands.

116. Assertion A) Instruction SIM is

necessary to implementthe interrupts INTR.

Reason R) INTR requires external

hardware for implemen

tation .

117. Assertion A) STACK is used to tempo

rarily store the data in

RAM locations specifiedby the programmer in

main program.

Reason R) PUSH and POP instruc-tions are used to send or

retrieve the data from theSTACK .

118 . Assertion A) Coherent FSK system ispreferred to non-coherent

FSK.

Reason R) Coherent FSK requires

less power than non-

coherent FSK .119. Assertion A) In the FM receiver

discriminator, both thesum of the voltages and

ratios of the voltages areindependent of frequency.

Reason R) The diodes face the same

direction and the

discriminator requires alimiter to reject

amplitude changes of the

carrier voltage .

120 . Assertion A) n the power line

communication, carrierfrequency is chosen

between 50 - k z and500 kHz.

Reason R) No extra lines are

necessary for the purposeand the same lines are

used to carry both theelc _ r i c power and

information by carriers.


18/20

SP CE OR ROUGH WORK


19/20

SP CE OR ROUGH WORK


20/20

SP CE FOR ROUGH W O R K

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