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CDAC Placement-Paper Electronics-Communication-Engineering Electrical and Electronics-04 Jan 2013


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 CDAC Electrical and electronics questions with answers

1.  Two 100-W, 200-V lamps are connected in series across a 200-V supply. The total power consumed by each lam will be _____ watts.

(a) 200

(b) 100

(c) 50

(d) 25  (Ans)

 

2. Kirchhoff’s voltage law is nt valid for a non-linear network.

(a) True

(b) False   (Ans)

 

3. The material used for fuse must have

(a) low melting point and low specific resistance

(b) high melting point and low specific resistance

(c) low melting point and high specific resistance  (Ans)

(d) none of these

 

4. If a piece of metal wire is stretched, its resistance will increase.

(a) True   (Ans)

(b) False

 

5. The usual value of the surge impedance of a telephone line is ____ ohm.

(a) 75  (Ans)

(b) 600

(c) 500

(d) 250

 

6. In mesh analysis of a network, all the mesh current must necessarily be either clock-wise or anticlock-wise.

(a) True   (Ans)

(b) False

 

7. The purpose of introducing reactor in the ignition circuit of mercury are rectifier is to limit the

(a) voltage of the circuit

(b) rate  of change of flux in the circuit

(c) current in the circuit   (Ans)

(d) rate of change of current in the circuit

 

8.  An uncharged capacitor is connected across a charged one. There will flow an impulsive current through the circuit.

(a) True   (Ans)

(b) False

 

9.  In the case of a lossy capacitor, series equivalent  resistance value will be

(a) small  

(b) large   (Ans)

(c) very small

(d) none of these

 

10. Time constant of an R- C circuit increases if the value of resistance is

(a) decreased

(b) increased   (Ans)

(c) neither (a) nor (b)

(d) either (a) nor (b)

  

11. If R, L and C denote resistance, inductance and capacitance respectively, the quantity RC has the same dimensions as that of R/L.

(a) True  

(b) False   (Ans)

 

12. If R, L and C denote resistance, inductance and capacitance respectively, the quantity CR2 has the dimensions of L.

(a) True    (Ans)

(b) False

 

13. Sparking between contacts can be reduced by inserting a

(a) capacitor in parallel with contacts   (Ans)

(b) resistance in the line

(c) capacitor in series with contacts

(d) none of these

 

14. A battery will not cause any current to flow, when it is connected across a pure capacitor, in the steady state even if the capacitor value varies with time.

(a) True  

(b) False   (Ans)

 

15. Voltage stress is maximum in a cable at the surface of the

(a) insulator

(b) sheath

(c) conductor   (Ans)

(d) none of these

 

16. When two capacitors C1 and C2 are connected in series, the effective capacitance is C1 + C2

(a) True  

(b) False   (Ans)

 

17. Sparking occurs when a load is switched off because the circuit has high

(a) resistance   (Ans)

(b) inductance

(c) capacitance

(d) none of these

 

18. The flux linked with a coil of inductance L carrying a current is d/dt (Li) .

(a) True  

(b) False   (Ans)

 

19. The coefficient of coupling between two air core coils depends on

(a) mutual inductance and self inductances of the two coils   (Ans)

(b) mutual inductance between two coils only

(c) self inductances of the two coils only

(d) none of these

 

20.  The location of lightning arrestor is

(a) away from the transformer

(b) near the transformer   (Ans)

(c) near the circuit breaker

(d) none of these

 

21. A conductor of length 1 metre moves at rt. angles to a magnetic field of flux density 1 Wb/m2 with a velocity of 25 m/s. The induced e.m.f. in the conductor will be _______ volt.

(a) 75

(b) 25  (Ans)

(c) 50

(d) 100

 

22. In electrical machines, laminated cores are used with a view to reducing

(a) eddy current loss   (Ans)

(b) hysteresis loss

 

23. A battery

(a) always delivers power

(b) always absorbs power

(c) absorbs power when the internal resistance is non-zero but delivers power when the internal resistance is zero

(d) can absorb or deliver power depending upon the circuit to which it is connected   (Ans)

 

24.  When one wants to connect two batteries in parallel to draw larger current than what can be supplied by one battery, it suffices to ensure that their e.m.f.s. are equal.

(a) True    (Ans)

(b) False

 

25.  An ideal battery can supply infinite current

(a) True  

(b) False   (Ans)

 

26. Decibel is a

(a) unit of voltage

(b) unit of power

(c) ratio of power   (Ans)

(d) none of these

 

27. dBm is a

(a) ratio of power   (Ans)

(b) unit of power

(c) unit of voltage

(d) none of these

 

 

28. Decibel is a unit of

(a) frequency

(b) impedance

(c) power ratio   (Ans)

(d) none of these

 

29. The absolute unit of resistance is of the dimension of

(a) velocity   (Ans)

(b) length

(c) acceleration

(d) none of these 

 

30. The absolute unit of inductance is of the dimension of

(a)  time

(b) length   (Ans)

(c) mass

(d) none of these

 

31.  The applied voltage from the circuit being checked is disconnected  when an ohmmeter is used because

(a) the current will decrease the resistance

(b) the ohmmeter has its own battery

(c) no current is needed for meter movements

(d) the voltage source will increase the resistance   (Ans)

 

32. An accurate voltmeter must have an internal impedance of

(a) very high value   (Ans)

(b) very low value

(c) low value

(d) none of these

 

33.  A moving-coil instrument can be used to measure

(a) high frequency a.c.

(b) low frequency a.c.

(c) both d.c. and a.c

(d) direct current   (Ans)

 

34. The voltage drop across the moving coil of a 50-μA (f.s) PMMC meter at full-scale deflection is ___ the voltage drop across that of a 1-mA (fs) PMMC meter at full-scale deflection.

(a) less than

(b) approximately equal to   (Ans)

(c) greater than

(d) none of these

 

35. Deflection of pointer of a permanent-magnet moving-coil meter for fixed current is ______flux density in the air gap between magnetic pole shoes and coil.

(a) independent of

(b) directly proportional to   (Ans)

(c) inversely proportional to

(d) none of these

 

36. A moving-iron meter is useful for voltage measurement at _____ frequencies.

(a) high

(b) low   (Ans)

(c) very high

(d) none of these

 

37.  A thermocouple instrument would be useful for current measurement at _____ frequencies.

(a) low

(b) very low

(c) very high   (Ans)

(d) none of these

 

38. Which of the following instruments will be used to measure alternating current only ?

(a) moving-iron (attraction-type) ammeter

(b) moving-iron voltmeter

(c) permanent-magnet type ammeter

(d) induction-type ammeter   (Ans)

 

39. A milliammeter can be used

(a) only as an ammeter

(b) as a voltmeter

(c) both as voltmeter and ammeter   (Ans)

(d) none of these

 

40.  To measure the e.m.f. of a Weston standard cell, one would use a/an

(a) electrostatic voltmeter

(b) hot-wire voltmeter

(c) galvanometer

(d) potentiometer   (Ans)

 

41. Deflection sensitivity of deflecting plates of a cathode ray tube ___ the distance between deflection plates.

(a) is inversely proportional to    (Ans)

(b) is directly proportional to

(c) does not depend on

(d) none of these

 

42. Deflection sensitivity of deflecting plates of a cathode ray tube ____ the accelerating anode (A3) voltage.

(a) is inversely proportional to    (Ans)

(b) is directly proportional to

(c) does not depend on

(d) none of these

 

43. A moving-coil instrument can be used to measure

(a) direct current    (Ans)

(b) alternating current

(c) both direct current and alternating current

(d) none of these

 

44. The frequency stability of a crystal oscillator depends upon

(a) tuned circuit

(b) crystal    (Ans)

(c) crystal as well as the tuned circuit.

(d) none of these

 

45. Hay bridge is usually used for measuring

(a) resistance

(b) capacitance

(c) inductance    (Ans)

(d) none of these

 

46. Schering bridge is used for measuring

(a) capacitance    (Ans)

(b) inductance

(c) frequency

(d) none of these

 

47. The Wien's bridge is particularly useful for measuring frequencies of ____ value.

(a) low

(b) very high

(c) high    (Ans)

(d) very low

 

48. Impedance relay is used to protect

(a) line within a particular zone    (Ans)

(b) line beyond a particular zone

(c) the whole transmission system

(d) none of these

 

49.  Buchholz relay is used in ____ protection.

(a) line

(b) generator

(c) transformer    (Ans)

(d) none of these

 

50. 1 GHz means 109 Hz.

(a) True     (Ans)

(b) False  

 

 

51.  If e1 = A sin wt and e2 = B sin (wt - θ), then ___ by θ.

(a) e1 leads e2

(b) e2 leads e1

(c) elags e1   (Ans)

(d) elags  e2

 

52. Average value of a sine wave is √2 times the maximum value.

(a) True    

(b) False      (Ans)

 

53. Any resistive network, linear or non-linear will pass a non-sinusoidal wave-form without distortion.

(a) True    

(b) False      (Ans)

 

54. The error due to conductance of Q-meter tuning capacitor on the indicated Q _____ with increase in frequency.

(a) has no effect

(b) decreases

(c) increase    (Ans)

(d) none of these

 

55. Quality of a circuit  (Q-factor) increases by ____ bandwidth.

(a) increasing

(b) decreasing    (Ans)

 

56.  A current consists of a fundamental component of amplitude l1 and a third harmonic of amplitude l3. The rms value of the current will be

(a) lrms = √(l12 + l32

(b) lrms = √(l12 + l32)/2   (Ans)

(c) lrms = (l1 + l3)/2

(d) lrms = (l1 + l3)/2√2

 

57.  The impedance of a coil above self-resonant frequency is

(a) resistive

(b) capacitive

(c) inductive    (Ans)

(d) none of these

 

58. If  L, C and R denote inductance, capacitance and resistance respectively then √L/C has the dimensions of frequency.

(a) True    

(b) False      (Ans)

 

59. The solution of the second-order differential equation d2i / dt2 + 2  di/ dt + i = 0 will be of the form K1 e-t + K2 e-t

(a) True    

(b) False     (Ans)

 

60. A pure inductance having no initial energy is conducted across a pure capacitance having some initial energy. The current in the circuit will eventually decay to zero.

(a) True     (Ans)

(b) False  

 

61.  Floating neutral in a three phase supply is undesirable because it may give rise to

(a) low voltage across the load

(b) unequal line voltages across the load  (Ans)

(c) high voltage across the load

(d) none of these

 

62.  If the readings of the two watt-meters in the 2-wattmeter method of power measurement are 4.5 kW and 3.5 kW respectively and the latter reading has been obtained after reversing the current coil of the wattmeter. What will be the total power in kW?

(a) 8

(b) 4.5

(c) 3.5

(d) 1   (Ans)

 

63. Which of the following generating station has the minimum running cost ?

(a) diesel power plant

(b) thermal power station

(c) nuclear power station

(d) hydro-electric station   (Ans)

 

64. Charging current in a transmission line

(a) decreases line losses

(b) increases line losses  (Ans)

(c) increase the line current

(d) none of these

 

65.  The span of transmission line between towers takes the form of a

(a) catenary

(b) parabola  (Ans)

 

66.  Lightning arrestors are located at the

(a) line entry point of the power house

(b) transformer terminal

(c) generator terminal

(d) tower top  (Ans)

 

67.  It is important to control power factor in supply systems and equipments for

(a) increasing apparent power

(b) regulation  (Ans)

 

68.  The highest transmission line voltage in India today is ____ kV.

(a) 750

(b) 220

(c) 600

(d) 400     (Ans)

 

69. Shunt capacitance is neglected while considering a ______ transmission line

(a) long

(b) short    (Ans)

(c) medium

(d) very long

 

70.  The efficiency of a d.c. shunt generator is maximum when the

(a) stray losses are equal to the copper losses

(b) magnetic losses are equal to the mechanical losses

(c) armature copper losses are equal to constant losses     (Ans)

(d) field copper losses are equal to the constant losses

 

71.  A 4-pole lap-connected D.C. shunt generator generates a voltage of 230 V. If the pole number is reduced to two without changing the flux, the number of armature conductors and speed, the machine will generate a voltage of ____ volt.  

(a) 460

(b) 115

(c) 0

(d) 230    (Ans)

 

72. In a dc generator, the brushes on the commutator at shifted from geometrical neutral positions to

(a) avoid sparking     (Ans)

(b) obtain highest generator voltage

 

73. A dc generator generates

(a) ac voltage     (Ans)

(b) dc voltage

 

 

74. A dc generator can be termed as a

(a) power pump

(b) rotating amplifier     (Ans)

(c) prime mover

(d) none of these

 

75. The mechanical power developed by a d.c. motor is maximum when the back e.m.f. is

(a) approaching the value of the applied voltage

(b) equal to the applied voltage

(c) equal to zero

(d) equal to half the applied voltage     (Ans)

 

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