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single phase induction motors MCQs

Practise focused single phase induction motors questions with marked answers for exam preparation and subject revision.

single phase induction motors Mcqs
1. The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the ground will be___________?
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A. at the slot edge where coil enters or comes out of the slot

B. at the end connections

C. at the end terminals

D. anywhere on the winding inside a slot

2. Which of the following motor will give the highest starting torque ?
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A. D.C. shunt motor

B. Repulsion start and induction run motor

C. Universal motor

D. Schrage motor
3. The power factor of a single-phase induction motor is usually?
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A. always leading

B. lagging

C. unity

D. unity to 0.8 leading

4. Which of the following motors is used in a situation where load increases with speed ?
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A. Hysteresis motor

B. Induction motor

C. Three-phase series motor

D. Schrage motor

5. In split phase motor main winding is of _____________?
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A. thin wire placed at the bottom of the slots

B. thick wire placed at the top of the slots

C. thin wire placed at the top of the slots

D. thick wire placed at the bottom of the slots
6. A schrage motor can run on___________?
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A. positive slip

B. zero slip

C. all of the above

D. negative slip

7. A centrifugal switch is used to dis- connect starting winding when motor has___________?
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A. picked up about 50 to 70 per cent of rated speed

B. run for about 1 minute

C. picked up about 10 to 25 per cent of rated speed

D. run for about 5 minutes

8. After the starting winding of a single phase induction motor is disconnected from supply, it continues to run only on ______________?
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A. running winding

B. compensating winding

C. field winding

D. rotor winding

9. The range of efficiency for shaded pole motors is______________?
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A. 80% to 90%

B. 5% to 35%

C. 95% to 99%

D. 50% to 75%

10. A single-phase induction motor is__________?
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A. inherently non-self-starting with low torque

B. inherently self-starting with low torque

C. inherently non-self-starting with high torque

D. inherently self-starting with high torque

11. In a single phase motor the centrifugal switch____________?
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A. reconnects the auxiliary winding of the motor

B. disconnects auxiliary winding of the motor

C. reconnects the main winding the motor

D. disconnects main winding of the motor

12. In a split phase motor____________?
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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. centrifugal switch is used to control supply voltage

13. Starting winding of a single phase motor of a refrigerator is disconnected from the circuit by means of a___________?
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A. thermal relay

B. none of the above

C. centrifugal switch

D. magnetic relay
14. If the capacitor of a single-phase motor is short-circuited_________?
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A. the motor will not start

B. the motor will run in reverse direction

C. the motor will run in the same direction at reduced r.p.m

D. the motor will run

15. Hysteresis motor is particularly useful for high-quality record players and tape-recorders because___________?
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A. it revolves synchronously

B. it is not subject to any magnetic or mechanical vibrations

C. it can be easily manufactured in extremely small sizes of up to 1 W output

D. it develops hysteresis torque which is extremely steady both in amplitude and phase
16. If starting winding of a single-phase induction motor is left in the circuit, it will____________?
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A. spark at light loads

B. run faster

C. run slower

D. draw excessive current and overheat
17. The direction of rotation of universal motor can be reversed the by reversing the flow of current through__________?
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A. none of the above

B. field winding

C. armature winding

D. either armature winding or field winding
18. Which of the following statements regarding repulsion-start induction motor is incorrect ?
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A. In fractional horse power motors, it has replaced the capacitor motors

B. It is not easily reversed

C. It requires more maintenance of commutator and other mechanical devices

D. It makes quite a bit of noise on starting

19. The speed of a universal motor is generally reduced by using_________?
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A. gear trains

B. V-belts

C. chains

D. brakes

20. In repulsion motor, maximum torque is developed when____________?
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A. none of the above

B. brush axis coincides with the field axis

C. brush axis is at 90 electrical to the field axis

D. brush axis is at 45 electrical to the field axis
21. Centrifugal switch disconnects the auxiliary winding of the motor at about ______ percent of synchronous speed?
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A. 30 to 40

B. 100

C. 70 to 80

D. 80 to 90

22. The motor used on small lathes is usually_________?
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A. D.C. shunt motor

B. 3-phase synchronous motor

C. universal motor

D. single-phase capacitor run motor
23. In repulsion motor direction of rotation of motor____________?
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A. is independent of brush shift

B. is opposite to that of brush shift

C. is the same as that of brush shift
24. The motor used for the compressors is____________?
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A. capacitor-start capacitor-run motor

B. d.c. series motor

C. reluctance motor

D. shaded pole motor

25. Which of the following motors can be run on AC. as well as D.C. supply ?
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A. Reluctance motor

B. Synchronous motor

C. Universal motor

D. Repulsion motor

26. The rotor slots, in an induction motor, are usually not quite parallel to the shaft because it_____________?
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A. helps in reducing the tendency of the rotor teeth to remain under the stator teeth

B. improves the efficiency

C. helps the rotor teeth to remain under the stator teeth

D. improves the power factor

27. Which of the following motors will operate at high power factor ?
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A. Split phase motor

B. Capacitor run motor

C. Shaped pole motor

D. Capacitor start motor

28. Which of the following motors can be used for unity power factor ?
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A. Shaded pole motor

B. Schrage motor

C. Capacitor run motor

D. Hysteresis motor

29. The rotor developed by a single-phase motor at starting is___________?
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A. less than the rated torque

B. zero

C. more than i.he rated torque

D. rated torque

30. Speed torque characteristic of a repulsion induction motor is similar to that of a D.C____________?
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A. series motor

B. shunt motor

C. compound motor

D. separately excited motor

31. Which of the following single-phase motors is suitable for timing and control purposes ?
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A. Series motor

B. Repulsion motor

C. Universal motor

D. Reluctance motor
32. In a universal motor, the most common cause of brush sparking is___________?
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A. shorted armature winding

B. shorted field winding

C. open armature winding

D. high commutator mica

E. all of the above
33. In a split phase motor, the running winding should have?
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A. high resistance and low inductance

B. low resistance and high inductance

C. low resistance as well as low inductiance

D. high resistance as well as high inductance

34. If a D.C. series motor is operated on A.C. supply, it will____________?
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A. spark excessively

B. have poor power factor

C. all of the above

D. have poor efficiency

35. When a D.C. series motor is connected to A.C. supply, the power factor will be low because of____________?
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A. high inductance of field and armature circuits

B. induced current in rotor due to variations of flux

C. none of the above

D. fine copper wire winding

36. Which of the following motors is preferred for tape-recorders ?
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A. Hysteresis motor

B. Two value capacitor motor

C. Universal motor

D. Shaded pole motor

37. In A.C. series motor compensating winding is employed to_____________?
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A. none of the above

B. increase the torque

C. reduce sparking at the brushes

D. reduce the effects of armature reaction

38. In a capacitor start single-phase motor, when capacitor is replaced by a resistance____________?
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A. the motor will consume less power

B. torque will increase

C. motor will run in reverse direction

D. motor will continue to run in same direction
39. Locked rotor current of a shaded pole motor is____________?
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A. several times the full load current

B. slightly more than full load current

C. less than full load current

D. equal to full load current

40. In split-phase motor auxiliary winding is of___________?
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A. thick wire placed at the top of the slots

B. thin wire placed at the top of the slots

C. thin wire placed at the bottom of the slots

D. thick wire placed at the bottom of the slots

41. Which of the following statements regarding two value capacitor motor is incorrect ?
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A. It has low starting as well as rushing currents

B. It has high starting torque

C. It is a reversing motor

D. It is preferred to permanent-split single-value capacitor motor where frequent reversals are required
42. In which single-phase motor, the rotor has no teeth or winding ?
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A. Universal motor

B. Split phase motor

C. Reluctance motor

D. Hysteresis motor
43. In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to_______________?
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A. to improve torque

B. reduce fluctuations in torque

C. improve power factor

D. increase overload capacity

44. The electric motor used in portable drills is__________?
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A. capacitor run motor

B. universal motor

C. repulsion motor

D. hysteresis motor

45. As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for__________?
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A. fans

B. sound equipment

C. mixer grinders

D. blowers

46. The direction of rotation of an hysteresis motor is determined by____________?
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A. interchanging the supply leads

B. retentivity of the rotor material

C. position of shaded pole with respect to main pole

D. none of these

47. In repulsion motor, zero torque is developed when___________?
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A. brush axis is 45 electrical to field axis

B. brush axis coincides with the field axis

C. brush axis is 90 electrical to field axis

D. both B. and (c)
48. Short-circuiter is used in_____________?
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A. none of the above

B. repulsion induction motor

C. repulsion start induction run motor

D. repulsion motor

49. The capacitors used in single-phase capacitor motors have no__________?
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A. voltage rating

B. dielectric medium

C. polarity marking

D. definite value

50. The repulsion-start induction-run motor is used because of___________?
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A. high starting torque

B. good power factor

C. minimum cost

D. high efficiency