Electrical Engineering 1 Drdo

8/9/2019 Electrical Engineering 1 Drdo

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ELECTRICAL ENGINEERING

PRACTICE SET-1

Q.1:- The resistance of a strip of copper of rectangular cross-section is 2Ω. A

metal of resistivity twice that of copper is coated on its upper surface to a

thickness equal to that of copper strip. The resistance of composite strip will be

(a !Ω (b "#$Ω (c $#2Ω (d $#"Ω

Q.2:- The electric %eld lines and equipotential lines

(a Are parallel to each other.(b Are one and the same.(c &ut each other orthogonally.(d &an be inclined to each other at any angle.

Q.3:- 'or an &)* di#dt protection is achieved through the use of

(a ) in series with &).(b + in series with &).(a )+ in series with &).(c )+& in series with &).

Q.4:- ,n a linear system* an input of sin wt produces an output of / cos wt.

The output corresponding to input / cos wt will be equal to

(a 0 sin wt (b - sin wt (c 0 2/ sin wt (d 1 2/ sin wt.

Q.5:- 'or the system shown in %gure* with a damping ratio of /.3 and an

undamped natural frequency w n of " rad # sec* the values of 4 and are

(a 4 5 "* a 5 /.$(b 4 5 6* a 5 /."

(c 4 5 !* a 5 /.22(d 4 5 !"* /.7

Q.6:- A single instruction to clear the lower four bits of the accumulator , 6/6

assembly language is8

(a 9), :;' (b A


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(b A dc ground potential.(c The most positive potential available in the circuit.(d The most negative potential available in the circuit.

Q.8:- The velocity of electromagnetic ratio waves is

(a $ ? 106m/s

(b $ ? 108

m/s

(c $ ? 1010m/ s

(d $ ? 1012m/s

Q.9:- A certain 6- bit microprocessor e?ecutes @B A* BC by loading B to the

A+* then loading A to the A+* ubtracting A from B* and storing the result in B.

Dhich of the following instructions would cause the EF): >ag to be setG

(a B 1 (9* (9 0

(b B 9* (9 0(c B 1 ( 9* (9(d all of the above

Q.10:- which of the following induction motor will have the least shaft diameterG

(a 2/ ;H* 266/ rpm(b 2/ ;H* ""/ rpm(c 2/ ;H* 7!/ rpm(d 2/ ;H* 3$/ rpm

Q.11:- ,n IplasmaJ state a gas

(a ( a loses electrical conductivity(b ( b attracts moisture(c ( c becomes perfect dielectric medium(d ( d conducts electricity

Q.12:- ,f the secondary winding of the ideal transformer shown in the %gure

below* has "/ turns* the number of turns in the primary winding for ma?imum

power transfer to the 2 ohm resistor will be

,KFA T)A


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Q.13:- A ! pole $-phase wound-rotor induction machine is driven by another

machine at 6// rpm. The rotor of the induction machine is connected to a /;M

system. ,f the mechanical rotation of the rotor is in the same direction as the

rotor winding >u? rotation* then frequency of the stator voltage will be

(a /;M (b "/ ;M (c / ;M (d 2// ;M

Q.14:- A universal motor runs at

(a ;igher speed will dc supply and with less sparking.(b ;igher speed with ac supply with less sparking.(c ame speed both ac and dc supplies.(d ;igher speed with ac supply but with increased sparking at the brushes.

Q.15:- Two / kNA alternator operate in parallel to supply the following loads

,. 2/ 4D at /.7 p.f. lagging,,. // 4D at /.6 p.f. leading

:ne machine is supplying 2// 4D at /.7 p.f. lagging. The p.f. of other

machine must be

(a /.67 leading (b /.7 leading (c /.7 lagging

(d /.67 lagging

Q.16:- ,n a / volts compound generator* the armature* shunt and series

windings are /./! ohm* 23. ohm and /./" ohm respectively. The load consists of

2// lampsO each rated at D* / N. %nd the total e.m.f. when the machine is

connected for long shunt operation.

(a 2 N (b 32 N (c // N (d

2/ N

Q.17:- Bagasse is

(a +ow quality coal.(b A fuel consisting of wood.(c 'ibrous portion of sugarcane left after e?tracting the =uice.(d A kind of rice straw.

Q.18:- The copper armature winding of a motor is sub=ected to an operating

temperature of 6/P&. The room temperature is 2/P &. The percentage change inresistance of the armature winding from cold staring condition to normal running

will be nearly8

(a /Q (b !Q (c 2/Q (d 2"Q

Q.19:- Lagnetic >u? density at a point distance ) due to an in%nitely long linear

conductor carrying a current is given by


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(a B 51

2 μ πR (b B 5 µ

2 R

(c B 5 µ

2 μ R (d B 5 µ

2 π R2

Q.20:- A Mener diode works on the principle of

(a Tunneling of charge carriers across the =unction.(b Thermionic emission.(c KiRusion of charge carriers across the =unction.(d ;oping of charge carriers across the =unction.

Q.21:- Two resistance //Ω S Ω S Ω are connected in series. ,f the errors

are speci%ed as standard deviations* the resultant error will be

(a S /Ω (b S /.!Ω (c S .6Ω (d S 2/Ω

Q.22:- The unit impulse response of a system is given as c (t 5 −4e−t

0!e2t.

The step response of the same system for U/ is equal to

(a $e2t 0"et0(b $e2t 0"et(c $e2t 0"et

(d −¿ $e2t 0"et

Q.23:- Dhich of the following statements is trueG

(a ):L is a )ead#Drite memory.

(b H& points to the last instruction that was e?ecuted.(c tack works on the principal of +,':.(d All instructions aRect the >ags.

Q.24:- ,f a transistor is operation with both of its =unctions forward biased* but

with the collector forward bias greater than the emitter-base forward bias* then it

is operating in ht

(a 'orward active mode.(b )everse saturation mode.(c )everse active mode forward saturation mode.

(d 'orward saturation mode.

Q.25:- Dhich type of transmission line will have the ma?imum value of

characteristic impedanceG

(a :pen wire line.(b Twin lead line.(c &oa?ial cable.(d All have same impedance.


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(a A. teel core . &opper(b B. )otor core 2. &opper alloy(c &. tator windings $. ilicon steel(d K. lip rings ". Lild steel

i. . Aluminum

&odes8-

(a A B & K$ 2 (b A B & K

" 2(c A B & K

" $ 2(d A B & K

$ " 2

Q.33:- The type of dc generator used for arc welding purposes is a

(a eries generator.(b hunt generator.(c &umulatively compounded generator.(d KiRerentially compound generator.

Q.34:- ,n power station practice @spinning reserveC is

(a )eserve generating capacity that is in operation but not in service.(b )eserve generation capacity that is connected to bus and ready to take the

load.(c )eserve generating capacity that is available for service but not in

operation.(d &apacity of the part of the plant that remains under maintenance.

Q.35:- A load that has a resistance of / ohms is to be connected to a supply

that has a constant voltage of 2/ volts. ,f it is desired that the current to the

load be varied from $ to amperes* what are the resistance and the current

rating of the series rheostat that permit this variationG

(a (a ohms* A (b / ohms* / A(b (c 2/ ohms* / A (d 2/ ohms* / A

Q.36:- La?wellJs divergence equation for the magnetic %eld is given by

(a (a ∇× B 5 / (b ∇.B=¿ /

(b (c ∇× B 5 ρ (d ∇ . B= ρ

Q.37:- Dhen a line commutated converter operates in the inverter mode

(a ,t draws both real and reactive power from the A.&. supply.(b ,t delivers both real and reactive power to the A.&. supply.(c ,t delivers real power to the A.&. supply.


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(d ,t draws reactive power from the A.&. supply.

Q.38:- Latch +ist- with +ist-2 and select the correct answer using the codes

given below the lists8

+ist- +ist-2

(Harameter measured (Bridge

A. Audio frequency . La?well bridgeB. ;igh Y inductor 2. ;ay bridge&. Kielectric loss $. Dien bridgeK. +ow Y inductor ". chering bridge

&odes8

(a A B & K

$ " 2

(b A B & K

$ 2 "

(c A B & K" 2 $

(d A B & K

" 2 $

Q.39:- Latch +ist- with +ist-2 and select the correct answer using the codes

given below the lists8

+ist- +ist-2

(Time functions (+aplace transforms

A. FZ[ (t-2 .2

S ²

B.d (t 2)dt 2.

1e−² s

S+2

&. t # 2 $.1

2 s ²

".1

2 s

Codes:

(a A B &

2 $

(b A B &

2 $ "

(c A B &

2 $

(d A B &


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$ "

Q.40:- Dhat is the distance of the following codeG

(a 2 (b $ (c " (d

Q.41:- The common-emitter short-circuit current gain of a transistor

(a ,s a monotonically increasing of the collector current I c .

(b is a monotonically decreasing function I c .

(c ,ncreases with I c for low

I c * reaches a ma?imum* and then

decreases in I c .

(d is not a function of I c .

Q.42:- Dhich of the following is circularly polariMed antennaG

(a ;elical (b yogi.uda (c mall circular loop (d Harabolicre>ector

Q.43:- A single instruction to clear the lower four bits of the accumulator in 6/6

assembly language is8

(a 9), :'; (b A


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(b Transformer A8 primary ∆ O secondary \

Transformer B8 primary ∆ O secondary ∆

(c Transformer A8 primary \ O secondary ∆

Transformer B8 primary ∆ O secondary ∆

(d Transformer A8 primary ∆ O secondary ∆

Transformer B8 Hrimary ∆ O secondary ∆

Q.47:- A centre Mero ammeters connected in the rotor circuit of a !-pole / ;M

induction motor makes $/ oscillations in one minute. The rotor speed is

(a 73/ (b 77/ (c // (d /$/

Q.48:- which of the following capacitor start split-phase induction motor will

have the largest value of capacitanceG

(a ] ;.H.* $"/ rpm(b ] ;.H.* 32 rpm(c ] ;.H. * "/ rpm(d ^ ;.H.* "/ rpm.

Q.49:- The most appropriate operating speed in rpm of generators used in

Thermal*


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2:-$'& ince no electric can e?ist along any surface* all points of which are at the

same potential* electric %eld lines and equipotential lines are orthogonal to each

other.

3 :-$ %& 'or an &)* di#dt protection is achieved through the used of + in series

with &). A snubber circuit connected across an &) is to suppress dv # dt.

4 :-$ d& in wt →−¿ &os wt

KiRerentiating

&os wt →−¿ 2 in wt

∴ An input of / &os wt will cause a

)esponse of 1 2/ in wt.

5:- $'& L (s 5

1+G ( s ) H (s )¿

G(s)¿

5

1+(1+as ) K / s(s+2)¿

K / s(s+2)¿

The changed equation is

s (s02 0 4 ( 0 as 5 / or s[ 0 s (20ak 0 k 5/

&ompare with s[02

δ n s0

wn²

5 /

∴ 4 5wn² 5 "[ 5 !O

2δwn 5 (20ak

∴ a52×0.7×4−2

16 53.6

16 5 /.22


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6:- $%& A single instruction to clear the lower four bits of the accumulator in 6/6

assembly language is Aag will be set.

10:- $(& The horsepower is proportional to the product of rpm (ected resistance in

the primary circuit should be 6 ohm.

Therefore*

N 1

N 2 5 2 so that R

2'

5 (

N 1

N 2 [ ? R

2


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:r R

2 5 2[ ? 2 6 ohm

Thus*


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∴ The second machine will operate at leading

p.f. H` of this machine is

$/ 1 2// 5 / kD

∴ &os ` 5 tan cosZ76.67

150

5 /.67/ leading.

16:- $d& ra 5 /./! ohm

rs 5 23. ohm

rs 5 /./"

Total load current.

I ! 5 2// ?55

110 5 // A

I s 5110

27.5 5 " A.

I a 5

I ! 0 I s 5 // 0 " 5 /"A

emf 5 / 0 /" (/./! 0 /./" 5 2/." N.

17:- $'& Bagasse is %brous portion of sugarcane left after e?tracting the =uice.

18:- $'& 'or the present problem* the readers should consider armature as a

copper conduction through which the current >ows.

De know that for copper

" 5 /.//$7$ (at 2/P&

;ence* R

80 5 R

20 0 " (6/ 1 2/

5 R

20+ R

20 . " 9 !/

∴ R80− R

20

R20 5/.//$7$ ? !/ 5 2.$6


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:pen 1 wire line $// 1 !// Ω

Twin 1 lead line 2/ 1 $// Ω

&oa?ial cable / 1 3 Ω

26:- $(& 3 A / // / //

A2 // /// 0 // /

/ ///

)esult 5 K6VW.

ign bit 5 * so negative >ag set. The sign of the result is the same as the

sign of the number subtractedO thus. :ver>ow >ag set.

27:- $%& Lain purpose of peak load plant is to meet the peaked demand. uch

plants normally run for short durations and* therefore* their eXciency is a

secondary consideration.

28:- $'& Dhen a conductor is moved towards the north pole of a bar magnet* if

will e?perience a change of magnetic >u? as a result of which there will be an

induced emf. This emf will give rise to an induced current in the conductor* in a

direction (determined by +enMJs law that will oppose the movement of the

conductor. uch currents are called eddy currents.

,n general* eddy currents occur in conductors that e?perience a change of

>u?. This >u? change can be due either to the mechanical motion in a magnetic

%eld as in the armature of a motor* or to a changing current in the wires wound

around the soft iron core of a transformer. ,n both cases* eddy currents cause i[ )

losses due to heating. These can be minimiMed by laminating the iron core* i.e.*building it up with thin sheets covered by a thin coating of insulating varnish. This

reduces the eddy currents.

29:- $d& LagnetiMing current is usually non-sinusoidal at the >u? density values

normally usedO and under no load condition* the total current comprises

magnetiMing current and core loss component correct.

30:- $(& +enMJs law

30:- $%& )eluctance motor.

32:- $d& A - $* B 1 "* & 1 * K 1 2.

33:- $d& As the terminal voltage should fall with increase in the arc current for

welding work* the diRerentially compounded generator is quite suited for this

purpose.

34:- $%& ,n power station practice @spinning reserveC is to reserve generating

capacity that is connected to bus and ready to take the load.

35:- $'& The / ohm load when connected to 2/ N supply with take a current of

2/#/ 52A without rheostat in the circuit. ince it is desired to restrict the


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increase as the load increases. The crack will e?tend and a brittle fracture will

take place.

46:- $%& Fven (c is possible because we can have the phase group as yd and

Ky or yd and Ky . (b is impossible because there shall be a phase

diRerence of $/P in the voltages of the corresponding phases of the two-

transformers on the secondary side.

47:- $%& )otor frequency f` 5 /. ;O

f` 5 sf

s 50.5

50 5 /./

N s 5120 f

P 5120×50

6 5///

N r 5 N s ( 1 s

5 /// ( 1 /./ 5 77/ rpm

48:- $d& :ut of the given range of motors* motor at (d will require highest

torque. Therefore* capacitor in the au?iliary winding for this motor would have the

largest value.

49:- $%& Thermal power plant generators are invariably high speed machines.


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Electrical Engineering 1 Drdo