Single Phase Induction Motors MCQs

1. In repulsion motor direction of rotation of motor

(a) is opposite to that of brush shift
(b) is the same as that of brush shift
(c) is independent of brush shift

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Answer. b

2. The value of starting capacitor of a fractional horse power motor will be

(a) 100 uF
(6) 200 uF
(c) 300 uF
(d) 400 uF

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Answer. c

3. If a particular application needs high speed and high starting torque, then which of the following motor will be preferred?

(a) Universal motor
(b) Shaded pole type motor
(c) Capacitor start motor
(d) Capacitor start and run motor

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Answer. a

4. A centrifugal switch is used to dis- connect ‘starting winding when motor has

(a) run for about 1 minute
(b) run for about 5 minutes
(c) picked up about 50 to 70 per cent of the rated speed
(d) picked up about 10 to 25 per cent of the rated speed

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Answer. c

5. In a shaded pole single-phase motor, the revolving field is produced by the use of

(a) inductor
(b) capacitor
(c) resistor
(d) shading coils

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Answer. d

6. In a shaded pole motor, the shading coil usually consist of

(a) a single turn of heavy wire which is in parallel with running winding
(b) a single turn of heavy copper wire which is short-circuited and carries only induced current
(c) a multilayer fine gauge copper wire in parallel with running winding
(d) none of the above

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Answer. b

7. Which of the following motor will have relatively higher power factor?

(a) Capacitor run motor
(b) Shaded pole motor
(c) Capacitor start motor
(d) Split phase motor

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Answer. a

8. Which of the following motor will give relatively high starting torque?

(a) Capacitor start motor
(b) Capacitor run motor
(c) Split phase motor
(d) Shaded pole motor

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Answer. a

9. The rotor developed by a single-phase motor at starting is

(a) more than the rated torque
(b) rated torque
(c) less than the rated torque
(d) zero

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Answer. d

10. In a split phase motor

(a) the starting winding is connected through a centrifugal switch
(b) the running winding is connected through a centrifugal switch
(c) both starting and running windings are connected through a centrifugal switch
(d) the centrifugal switch is used to control supply voltage

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Answer. a

11. In a capacitor start motor, the phase displacement between starting and running winding can be nearly

(a) 10°
(b) 30°
(c) 60°
(d) 90°

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Answer. d

12. In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to

(a) improve power factor
(b) increase overload capacity
(c) reduce fluctuations in torque
(d) to improve torque

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Answer. a

13. In capacitor start single-phase motors

(a) current in the starting winding leads the voltage

(b) current in the starting winding lags the voltage
(c) current in the starting winding is in phase with voltage in running winding
(d) none of the above

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Answer. a

14. If the capacitor of a single-phase motor is short-circuited

(a) the motor will not start
(b) the motor will run
(c) the motor will run in the reverse direction
(d) the motor will run in the same direction at reduced r.p.m.

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Answer. a

15. In a split phase motor, the running winding should have

(a) high resistance and low inductance
(b) low resistance and high inductance
(c) high resistance as well as high inductance
(d) low resistance as well as low inductance

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Answer. b