Objective Type Questions on Motor

1. Which of the following statements regarding a reluctance motor is incorrect ?

(a) It cannot be reversed, ordinarily.
(b) It requires no D.C. field excitation for its operation.
(c) It is nothing else but a single-phase, salient pole synchronous-induction motor.
(d) Its squirrel cage rotor is of unsymmetrical magnetic construction in order to vary reluctance path between stator and rotor.


Answer: (a) It cannot be reversed, ordinarily.
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2. A universal motor is one which

(a) can be operated either on D.C. or A.C. supply at approximately the same speed and output
(b) can be marketed internationally
(c) runs at dangerously high speed on no-load


Answer: (a) can be operated either on D.C. or A.C. supply at approximately the same speed and output .
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3. A repulsion motor is equipped with

(a) slip-rings
(b) commutator
(c) both
(d) none of the above


Answer: (b) commutator
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4. The capacitors used in single-phase capacitor motors have no

(a) voltage rating
(b) dielectric medium
(c) polarity marking
(d) definite value


Answer: (c) polarity marking
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5. If a D.C. series motor is operated on A.C. supply, it will

(a) spark excessively
(b) have poor efficiency
(c) have poor power factor
(d) all of the above


Answer: (d) all of the above
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6. Which of the following statements regarding repulsion-start induction motor is incorrect ?

(a) It requires more maintenance of commutator and other mechanical devices.
(b) It makes quite a bit of noise on starting.
(c) In fractional horse power motors, it has replaced the capacitor motors.
(d) It is not easily reversed.


Answer: (c) In fractional horse power motors, it has replaced the capacitor motors.
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7. A.C. series motor as compared to D.C. series motor has

(a) smaller brush width
(b) less number of field turns
(c) more number of armature turns
(d) less air gap
(e) all of the of the above


Answer: (e) all of the of the above
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8. Locked rotor current of a shaded pole motor is

(a) equal to full load current
(b) less than full load current
(c) slightly more than full load current
(d) several times the full load current


Answer: (d) several times the full load current
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9. Speed control of a universal motor is achieved by

(a) varying field flux with tapped field windings
(b) connecting rheostat in series
(c) applying variable voltage by means of silicon controlled rectifier
(d) applying variable voltage by means of variable auto-transformer
(e) all of the above methods


Answer: (e) all of the above methods
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10. Hysteresis motor is particularly useful for high-quality record players and tape-recorders because

(a) it revolves synchronously
(b) it is not subject to any magnetic or mechanical vibrations
(c) it can be easily manufactured in extremely small sixes of up to 1 W output
(d) it develops hysteresis torque which is extremely steady both in amplitude and phase


Answer: (d) it develops hysteresis torque which is extremely steady both in amplitude and phase.
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11. Which of the following statements regarding hysteresis motor is incorrect.

(a) It is extremely sensitive to fluctuations in supply voltage.
(b) Its high starting torque is due to its high rotor hysteresis loss.
(c) It is extremely quiet in operation.
(d) It accelerates from rest to high speed almost instantaneously.


Answer: (a) It is extremely sensitive to fluctuations in supply voltage.
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12. The starting winding of a single-phase motor is placed in

(a) armature
(b) field
(c) rotor
(d) stator


Answer: (d) stator
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13. The speed of a universal motor is usually reduced by using

(a) gearing
(b) belts
(c) brakes
(d) chains


Answer: (a) gearing
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14. In case of a reluctance motor, when the load is increased so that it cannot main maintain synchronous speed, the motor will

(a) become unstable
(b) draw excessive armature current and may burn out
(c) fall out of synchronism and come to stand still
(d) run as induction motor


Answer: (d) run as induction motor
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15. Which of the following motors would you select for vacuum cleaners ?

(a) Reluctance motor
(b) Universal motor
(c) Hysteresis motor
(d) Repulsion motor


Answer: (b) Universal motor
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16. Which of the following single-phase motors will be cheapest ?

(a) reluctance motor
(b) capacitor start motor
(c) capacitor run motor


Answer: (b) capacitor start motor
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17. Which of the following applications would need the smallest size of motor ?

(a) Table fan
(b) Sewing machine
(c) Domestic mixi
(d) Electric clock


Answer: (d) Electric clock
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18. In a shaded-pole motor, rotating magnetic field is produced by using

(a) salient poles
(b) shading coils
(c) copper windings
(d) a capacitor


Answer: (b) shading coils
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19. In a split-phase motor the ratio of number of turns for starting winding to that for running winding is

(a) less than one
(b) more than one
(c) one
(d) two


Answer: (a) less than one
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20. In a hysteresis motor, the rotor

(a) has high hysteresis loss
(b) high retentivity
(c) made of chrome steel
(d) should have all of the above features


Answer: (d) should have all of the above features
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21. In universal motor, normally the ratio of width of brush to the width of commutator segments is

(a) 6:1
(b) 4:1
(c) 2:1
(d) 1:1


Answer: (c) 2:1
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22. Shading coils in case of a shaded pole motor, are used to

(a) protect against sparking
(b) reduce windage losses
(c) reduce friction losses
(d) produce rotating magnetic field


Answer: (d) produce rotating magnetic field
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23. Which motor has unsymmetrical rotor?

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


Answer: (c) Reluctance motor
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24. If a single-phase motor runs hot the probable cause cannot be

(a) blown fuses
(b) low voltage
(c) high voltage
(d) shorted stator coils


Answer: (a) blown fuses
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25. For ceiling fans generally the single phase motor used is

(a) capacitor-start type
(b) split-phase type
(c) permanent capacitor type
(d) capacitor start and run type


Answer: (c) permanent capacitor type
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26. The direction of rotation of universal motor can be reversed by

(a) interchanging the brush lends
(b) switching over from A.C. to D.C.
(c) reversing the supply terminals
(d) any of the above


Answer: (a) interchanging the brush lends
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27. Which of the following is most economical method of starting a single-phase induction motor?

(a) Inductance-start method
(b) Split-phase method
(c) Resistance start method
(d) Capacitance-start method


Answer: (d) Capacitance-start method
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28. When a universal motor is operated on no-bad, its speed is limited by

(a) supply voltage frequency
(b) armature reaction
(c) windage and friction
(d) weight of the armature


Answer: (c) windage and friction
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29. What could be the size of a universal motor for use in vacuum cleaners ?

(a) 2 H.P.
(b) 1 H.P.
(c) 3/4 H.P.
(d) 1/4 H.P.


Answer: (c) 3/4 H.P.
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30. Which of the following applications make use of a universal motor?

(a) Portable tools
(b) Lathe machines
(c) Oil expeller
(d) Floor polishing machine


Answer: (a) Portable tools
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31. For the same rating which of the follow motors has the highest starting torque ?

(a) Synchronous motor 
(b) Universal motor
(c) Split-phase motor
(d) All have identical starting torque


Answer: (b) Universal motor
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32. A capacitor selected for capacitor-run motor should be rated for

(a) r.m.s. voltage
(b) average voltage
(c) peak voltage
(d) none of the above


Answer: (c) peak voltage
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33. If the ceiling fan, when switched on, runs at slow speed in the reverse direction, it can be concluded that

(a) capacitor is ineffective
(b) winding has burnt out
(c) bearings are worn out
(d) none of the above


Answer: (a) capacitor is ineffective
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34. By pushing and pulling the rotor shaft of a motor, we can check its

(a) end play
(b) side play
(c) firmness of mounting
(d) free shaft movement


Answer: (a) end play
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35. Electrical faults in a motor occur most commonly in its

(a) motor winding
(b) commutator
(c) control equipment
(d) brushes


Answer: (c) control equipment
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Objective Type Questions on Motor

 

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

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