Single Phase Motor Questions Answers

1. Which of the following motors can be used for unity power factor ?

(a) Capacitor run motor
(b) Shaded pole motor
(c) Hysteresis motor
(d) Schrage motor


Answer: (d) Schrage motor
SHOW ANSWER

2. When a D.C. series motor is connected to A.C. supply, the power factor will be low because of

(a) high inductance of field and armature circuits
(b) induced current in rotor due to variations of flux
(c) fine copper wire winding
(d) none of the above


Answer: (d) Schrage motor
SHOW ANSWER

3. The direction of rotation of universal motor can reversed the by reversing the flow of current through

(a) armature winding
(b) field winding
(c) either armature winding or field winding
(d) none of the above


Answer: (c) either armature winding or field winding
SHOW ANSWER

4. Which motor is normally free from mechanical and magnetic vibrations?

(a) Split phase motor
(b) Universal motor
(c) Hysteresis motor
(d) Shaded pole motor


Answer: (c) Hysteresis motor
SHOW ANSWER

5. A reluctance motor

(a) is self-starting
(b) is constant speed motor
(c) needs no D.C. excitation
(d) all of the above


Answer: (d) all of the above
SHOW ANSWER

6. In a hysteresis motor, the rotor must have

(a) retentivity
(b) resistivity
(c) susceptibility
(d) none of the above


Answer: (a) retentivity
SHOW ANSWER

7. The rotor of a hysteresis motor is made of

(a) aluminium
(b) cast iron
(c) chrome steel
(d) copper


Answer: (c) chrome steel
SHOW ANSWER

8. Which of the following applications always have some load whenever switched on ?

(a) Vacuum cleaners
(b) Fan motors
(c) Pistol drills
(d) All of the above


Answer: (c) Pistol drills
SHOW ANSWER

9. In repulsion motor, maximum torque is developed when

(a) brush axis is at 45 degrees electrical to the field axis
(b) brush axis coincides with the field axis
(c) brush axis is at 90 degrees electrical to the field axis
(d) none of the above


Answer: (a) brush axis is at 45 degrees electrical to the field axis
SHOW ANSWER

10. If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in

(a) damage to the starting winding
(b) damage to the centrifugal switch
(c) over-loading of running winding
(d) none of the above


Answer: (a) damage to the starting winding
SHOW ANSWER

11. Speed torque characteristic of a repulsion induction motor is similar to that of a D.C.

(a) shunt motor
(b) series motor
(c) compound motor
(d) separately excited motor


Answer: (b) series motor
SHOW ANSWER

12. In a ceiling fan employing capacitor run motor

(a) secondary winding surrounds the primary winding
(b) primary winding surrounds the secondary winding
(c) both are usual arrangements
(d) none of the above


Answer: (a) secondary winding surrounds the primary winding
SHOW ANSWER

13. The shaded pole motor is used for

(a) high starting torque
(b) low starting torque
(c) medium starting torque
(d) very high starting torque


Answer: (b) low starting torque
SHOW ANSWER

14. The rotor slots, in an induction motor, are usually not quite parallel to the shaft because it

(a) improves the efficiency
(b) helps the rotor teeth to remain under the stator teeth
(c) helps in reducing the tendency of the rotor teeth to remain under the stator teeth
(d) improves the power factor


Answer: (c) helps in reducing the tendency of the rotor teeth to remain under the stator teeth
SHOW ANSWER

15. The speed/load characteristics of a universal motor is same as that of

(a) A.C. motor
(b) D.C. shunt motor
(c) D.C. series motor
(d) none of the above


Answer: (c) D.C. series motor
SHOW ANSWER

16. The motor used for the compressors is

(a) D.C. series motor
(b) shaded pole motor
(c) capacitor start capacitor run motor
(d) reluctance motor


Answer: (c) capacitor start capacitor run motor
SHOW ANSWER

17. In repulsion motor, zero torque is developed when

(a) brush axis is 45 degrees electrical to field axis
(b) brush axis coincides with the field axis
(c) brush axis is 90 degrees electrical to field axis
(d) either brush axis coincides with the field axis or brush axis is 90 degrees electrical to field axis


Answer: (d) either brush axis coincides with the field axis or brush axis is 90 degrees electrical to field axis
SHOW ANSWER

18. Centrifugal switch disconnects the auxiliary winding of the motor at about……………. percent of synchronous speed.

(a) 30 to 40
(b) 70 to 80
(c) 80 to 90
(d) 100


Answer: (b) 70 to 80

SHOW ANSWER

19. Starting winding of a single phase motor of a refrigerator is disconnected from the circuit by means of a

(a) magnetic relay
(b) thermal relay
(c) centrifugal switch
(d) none of the above


Answer: (a) magnetic relay
SHOW ANSWER

20. If a single phase induction motor runs slower than normal, the most likely defect is

(a) worn bearings
(b) short-circuit in the winding
(c) open-circuit in the winding
(d) none of the above


Answer: (a) worn bearings

SHOW ANSWER

21. Two-value capacitor motor finds increased application as compressor motor in small home air-conditioners because

(a) it is comparatively cheaper.
(b) it has almost non-destructible capacitor.
(c) it has low starting as well as running currents at relatively high power factor.
(d) it is quiet in operation.


Answer: (c) it has low starting as well as running currents at relatively high power factor.
SHOW ANSWER

22. lf the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then

(a) motor will not come up to speed
(b) motor will not carry the load
(c) current drawn by the motor will be excessively high
(d) electrolytic capacitor will in all probability, suffer break down


Answer: (d) electrolytic capacitor will in all probability, suffer break down
SHOW ANSWER

23. In a universal motor, the most common cause of brush sparking is

(a) open armature winding
(b) shorted armature winding
(c) shorted field winding
(d) high commutator mica
(e) all of the above


Answer: (e) all of the above
SHOW ANSWER

24. If starting winding of a single-phase induction motor is left in the circuit, it will

(a) run faster
(b) spark at light loads
(c) draw excessive current and over heat
(d) run slower


Answer: (c) draw excessive current and over heat
SHOW ANSWER

25. Most of the fractional horsepower motors have either

(a) hard and annealed bearings
(b) ball or roller bearings
(c) soft and porous bearings
(d) plain or sleeve bearings


Answer: (d) plain or sleeve bearings
SHOW ANSWER

26. Which of the following statements regarding reluctance-start motor is incorrect ?

(a) It is similar to reluctance motor.
(b) It is basically an induction motor and not a synchronous one.
(c) So far as its basic working principle is concerned, it is similar to shaded polo motor.
(d) The air-gap between rotor and salient poles is non- uniform.


Answer: (a) It is similar to reluctance motor.
SHOW ANSWER

27. To reverse the direction of rotation of a capacitor-start motor while it is running we should

(a) disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary winding
(b) disconnect motor from supply and immediately reconnect it to supply with reversed connections of the main winding
(c) reverse the direction of connection of the auxiliary winding and after motor comes to rest then connect auxiliary winding to the supply
(d) reverse the direction of connections of the auxiliary winding and immediately connect it to supply


Answer: (a) disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary winding
SHOW ANSWER

28. When a ceiling fan employing a capacitor run motor is switched on it hums but does not burn. When it is driven by external means, it runs in whatever direction it is made to run. The trouble is due to

(a) blown fuse
(b) short in the capacitor
(c) an open in centrifugal switch
(d) an open in capacitor


Answer: (d) an open in capacitor
SHOW ANSWER

29. Which of the following motors has two separate windings on the motor ?

(a) Repulsion motor
(b) Repulsion induction motor
(c) Repulsion start induction run motor
(d) None of the above


Answer: (b) Repulsion induction motor
SHOW ANSWER

30. As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for

(a) fans
(b) blowers
(c) sound equipment
(d) mixer grinders


Answer: (c) sound equipment
SHOW ANSWER

31. Reluctance motors are

(a) singly excited
(b) doubly excited
(c) either of the above
(d) none of the above


Answer: (a) singly excited
SHOW ANSWER

32. Which motor will make least noise?

(a) Hysteresis motor
(b) Capacitor motor
(c) Shaded-pole motor
(d) Universal motor


Answer: (a) Hysteresis motor
SHOW ANSWER

33. Which motor is relatively free from mechanical and magnetic vibrations?

(a) Shaded-pole motor
(b) Universal motor
(c) Reluctance motor
(d) Hysteresis motor


Answer: (d) Hysteresis motor
SHOW ANSWER

34. A single-phase capacitor-start motor will take starting current nearly

(a) four to six times the full load current
(b) three times the full load current
(c) twice the full load current
(d) same as full load current


Answer: (c) twice the full load current
SHOW ANSWER

35. For a system involving sound recording and reproduction which motor would you select ?

(a) Shaded-pole motor
(b) Universal motor
(c) Reluctance motor
(d) Hysteresis motor


Answer: (d) Hysteresis motor
SHOW ANSWER

Single Phase Motor Questions Answers

 

  1. MCQ on Single Phase Induction Motor
  2. Single Phase Motor Questions Answers
  3. Objective Type Questions on Motor

© www.yourelectricalguide.com/ single phase motor questions answers.

Leave a Comment

Your email address will not be published. Required fields are marked *