SSC JE Electrical MCQ

1. The voltage wave v = Vm sin (wt – 15°) volts is applied across an AC circuit. If the current leads the voltage by 10° and the maximum value of currents is Im, then the equation of current is

(a) i = Im sin (wt + 5°) amps
(b) i = Im sin (wt – 25°) amps
(c) i = Im sin (wt + 25°) amps
(d) i = Im sin (wt – 5°) amps

5. Resistance temperature coefficient of copper at 20°C is

(a) 0.0045/°C
(b) 0.0017/°C
(c) 0.00393/°C
(d) 0.0038/°C

6. The load characteristic of DC shunt generator is determined by

(a) the voltage drop in armature resistance
(b) the voltage drop due to armature reaction, voltage drop due to decreased field current and voltage drop in armature resistance
(c) the voltage drop to armature reaction and voltage drop in armature resistance
(d) the voltage drop due to armature reaction, voltage drop due to decreased field current and voltage drops in armature and field resistance

7. How many watt-seconds are supplied by a motor developing 2 hp (British) for 5 hours

(a) 2.6856 × 10⁷watt-seconds
(b) 4.476 × 10⁵watt-seconds
 (c) 2.646 × 10⁷watt-seconds
(d) 6.3943 × 10⁶watt-seconds

8. A 4-pole generator is running at 1200 rpm. The frequency and time period of the emf generated in its coils respectively

(a) 50 Hz, 0.02 sec
(b) 40 Hz, 0.025 sec
(c) 300 Hz, 0.00333 sec
(d) 2400 Hz, 1/2400 sec

9. The single phase Induction Motor (IM) which does not have centrifugal switch is

(a) capacitor start single phase IM
(b) resistance split single phase IM
(c) capacitor start capacitor run single phase IM
(d) permanent capacitor run single phase IM

10. When a multiplier is added to an existing voltmeter for extending its range, its electromagnetic damping

(a) remains unaffected
(b) increases
(c) decreases
(d) changes by an amount depending on the controlling torque

11. Phasor diagram of load voltage (V), current in pressure coil (Ip) and current in current coil (IC) is shown in the figure when an electrodynamic wattmeter is used to measure power. The reading of the wattmeter will be proportional to

12. Two parallel conductors carrying current in opposite directions will exert on each other

(a) an attractive forces
(b) a repulsive force
(c) an axial force
(d) no force

13. The unit of reluctance of magnetic circuit is

(a) AT/m
(b) Weber/m
(c) AT/Weber
(d) Weber/AT

14. In indicating instruments the springs are mainly used to

(a) conduct the current to the coils
(b) hold the pivot in position
(c) control the pointer movement
(d) reduce the vibration of the pointer

15. A balanced 3-phase, 3-wire supply feeds balanced star connected resistors. If one of the resistors is disconnected, then the percentage reduction in load will be

(a) 33.33
(b) 50
(c) 66.67
 (d) 75

16. The total flux at the end of a long permanent bar magnet is 100× 10^-6 Wb. The end of this magnet is withdrawn through a 1000 turn coil in 1/20 seconds. The induced e.m.f. in the coil is

(a) 20.0 V
(b) 2.0 V
(c) 0.2 V
(d) 0.02 V

17. In reference to the figure, the voltage waveform v(t) is measured by a PMMC, a PMMC combined with bridge rectifier and a moving iron (MI) instrument. Two lists are prepared thereafter . The correct option relation the instruments and their reading is

(a) a-i, b-ii, c-iii
(b) a-iii, b-ii, c-i
(c) a-ii, b-iii, c-i
(d) a-iii, b-i, c-ii

18. The switching transistor as shown, carries in the colletor side an rms current of 8 mA. If the frequency of rectangular pulse train Vi is 50 Hz, then on-time of the transistor is

(a) 20 ms
(b) 6.4 ms
(c) 12.8 ms
(d) 16 ms

19. A ammeter of resistance Rm is placed an arrangement as shown in the figure. Material of Rm, Rsh is copper whereas that of Rs, Rx is manganin. The condition for which the meter performance is compensated against temperature, is

(a) 1/R_m + 1/R_sh + = 1/R_s + 1/R_x
(b) R_m R_s = R_sh R_x
(c) R_m + R_s = R_sh  + R_x
(d) R_m //R_s = R_sh + R_s

20. If a 110 V, 50 Hz is applied across a PMMC voltmeter of full-scale range 0-220 V and internal resistance of 10kΩ, reading of the voltmeter will be

(a) 0 V
(b) 110 √2 V
(c) 78V
(d) 55V