Engg Services Electrical Engineering Objective Paper 2 2011
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Transcript of Engg Services Electrical Engineering Objective Paper 2 2011
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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
Serial No. [ 39321
TEST OOKLET ALECTRICAL ENGINEERINGPape r- I I( Time Allowed Two Hours (Maximum Marks 200
INSTRUCTIONS
1. IMMEDIATELY AFTER THE COMMENCEMENT OF THE EXAMINATION, YOU SHOULDCHECK THAT THIS TEST BOOKLET DOES NOT HAVE ANY UNPRrNTED OR TORNOR MISSrNG PAGES OR ITEMS, ETC. IF SO, GET IT REPLACED BY A COMPLETETEST BOOKLET. .
2. ENCODE CLEARLY THE TEST BOOKLET SERIES A. B. C OR D AS THE CASE MAYBE IN THE APPROPRIATE PLACE IN THE ANSWER SHEET.
3. You have to enter your Roll Number on . he Test f 1Booklet in the Box provided alongside . . DO NOT .write anything else on the Test Book le t . · .
4 This Test Booklet contains 120 items (questions). Each item comprises four responses(answers). Yo .u will select the response which you want to mark on the Answer Sheet.In case you feel that there is more than one correct response, mark the response which youconsider the best. In any case, choose ONLY ONE response for each item.
5. You have to mark all your responses ONLY on the separate Answer Sheet provided.
61
See directions in the Answer Sheet . .All items carry equal marks.Before you proceed to mark in the Answer Sheet the response to various items in the TestBooklet; you have to fill in some particulars in the Answer Sheet as per instructions sentto you with your Admission Certificate. .
8. After you have completed filling in all your responses on the Answer Sheet and the.examination has concluded, you should hand over . to the Invigilator only the Answer Sheet .You are permitted to take away with you the Test Booklet.
9. Sheets for rough work are appended in the Test Booklet at the end .10. Penalty for wrong answers :
THERE WILL BE PENALTY FOR WRONG ANSWERS MARKED BY A CANDIDATEIN THE OBJECTIVE TYPE QUESTION PAPERS.(i) There are four alternatives for the answer to every question . For each question for
which a wrong answer has been given by the candidate, / one-tbird (0 33) of the marksassigned to that question will be deducted as penalty.
(ii) If a candidate gives more than one answer, it will be treated as a wrong answer evenif one of the given answers happens to be correct and there will be same penalty asabove to that question.
(iii) f a question is left lHank, i.e., no answer is given by the candidate, there will be. n o penalty for that question.
[ 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-
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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.)
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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.)
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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
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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.)
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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.)
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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.)
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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.)
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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.)
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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.)
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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.
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SP CE OR ROUGH WORK
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SP CE OR ROUGH WORK
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SP CE FOR ROUGH W O R K