SSC JE Electrical MCQ

41. In a motor starter, the electromechanical contactor provides inherent protection against

(a) over-current
(b) short-circuit
(c) single-phasing
(d) under-voltage

43. In a semiconductor, the resistivity

(a) depends on temperature
(b) depends on voltage
(c) depends on current through it
(d) None of the above

44. A geyser is operated from 230V, 50 c/s mains. The frequency of instantaneous power consumed by the geyser is

(a) 25 c/s
(b) 50 c/s
(c) 100 c/s
(d) 150 c/s

45. Ampere-second is the unit of

(a) emf
(b) power
(c) electric charge
(d) energy

46. Two lossy capacitors with equal capacitance values and power factors of 0.01 and 0.02 are in parallel, and the combination is supplied from a sinusoidal voltage source. The power factor of the combination is

(a) 0.03
(b) 0.015
(c) 0.01
(d) 0.0002

47. A voltmeter when connected across a DC supply, reads 124 V. When a series combination of the voltmeter and an unknown resistance X is connected across the supply , the meter reads 4V. If the resistance of the voltmeter is 50k Ω  , the value of X is

(a) 1550k Ω  
(b) 1600k Ω
(c) 1.6k Ω  
(d) 1.5k Ω

48. The purpose of providing a choke in the tube-light is

(a) to eliminate the corona effects
(b) to avoid radio interference
(c) to improve power factor
(d) to limit current to appropriate value

49. In a 3-phase 400 V, 4-wire system, two incandescent lamps, one having 230 V, 100 W specification and the other 230 V, 200 W are connected between R phase-neutral and Y phase-neutral respectively. If the neutral wire breaks

(a) 100 W lamp will fuse first
(b) 200 W lamp will fuse first
(c) both the lamps will fuse together
(d) both the lamps will glow

50. A solenoid of inductance 250 mH and resistance 10Ω is connected to a battery. The time taken for the magnetic energy to reach 1/4^th of its maximum value is

(a) log_e(2)
(b) 10^-3 log_e(2)
(c) 25 log_e(2)
(d) 1/40 log_e(2)

Answer: (d) 1/40 log_e(2)

51. The peak value of the output voltage of a half wave rectifier is 100 V. The r.m.s value of the half-wave rectifier output voltage will be

(a) 100 V
(b) 50 V
(c) 70.7 V
(d) 35.35 V

52. The given circuit represents a

(a) Monostable multivibrator
(b) Astable multivibrator
(c) Schmitt trigger
(d) Bistable multivibrator

53. The input resistance of a FET is of the order of

(a) 100 Ω  
(b) 10 Ω
(c) 1 m Ω  
(d) 100 M Ω

54. In a series R-L circuit supplied from an sinusoidal voltage source, voltage across R and L are 3 V and 4 V respectively. The supply voltage is then

(a) 7 V
(b) 1 V
(c) 3.5 V
(d) 5

55. If the insulation resistance of 2m long sample of a cable is 10MW , then a 8m long sample of the same will have an insulation resistance of

(a) 40 MΩ  
(b) 2.5 MΩ
(c) 2 MΩ  
(d) 5.5 MΩ

56. An inductor is supplied from a sinusoidal voltage source. The magnetic field energy in the inductor changes from peak value to minimum value 10 msec. The supply frequency is

(a) 50 Hz
(b) 25 Hz
(c) 1 kHz
(d) 100 Hz

57. Two 2000 Ω, 2 watt resistors are connected in parallel. Their combined resistance value and wattage rating are

(a) 1000 Ω, 2 watt
(b) 1000 Ω, 4 watt
(c) 2000 Ω , 4 watt
(d) 1000 Ω , 2 watt

58. We have three resistances each of value 1 Ω , 2 Ω  and 3 Ω. If all the three resistances are to be connected in a circuit, how many different values of equivalent resistance are possible?

(a) Five
(b) Six
(c) Seven
(d) Eight

59. One B.O.T. unit is

(a) 1000 kWh
(b) 10 kWh
(c) 1 kWh
(d) 0.1 kWh

60. An electric heater draws 1000 watts from a 250 V source. The power drawn from a 200 V source is

(a) 800 W
(b) 640 W
(c) 1000 W
(d) 1562.5 W