D.C Motor: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive] DC Motor MCQ Questions And Answers

21. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking……….

(a) regenerative

(b) plugging

(c) dynamic braking

(d) none of the above

Ans: b

22. Which of the following motors one will choose to drive the rotary compressor?

(a) D.C. shunt motor

(b) D.C. series motor

(c) Universal motor

(d) Synchronous motor

Ans: d

23. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will……….

(a) increase

(b) decrease

 (c) remain same

(d) become zero

Ans: a

24. In Ward-Leonard control the lower limit of speed is imposed by……….

(a) residual magnetism of the generator

(b) core losses of motor

(c) mechanical losses of motor and generator together                                                                                       

(d) all of the above

Ans: a

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25. The main disadvantage of the Ward-Leonard control method is……….

(a) high initial cost

(b) high maintenance cost

(c) low efficiency at highest  loads 

(d) all of the above

Ans: d

26. Regenerative method of braking is based on that……….

(a) back e.m.f. is less than the applied voltage

(b) back e.m.f. is equal to the applied voltage

(c) back e.m.f. of rotor is more than the applied voltage

(d) none of the above

Ans: b

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27. The hysteresis loss in a D.C. machine least depends on………

(a) Frequency of magnetic reversals

(b) Maximum value of flux density

(c) Volume and grade of iron

(d) Rate of flow of ventilating air

Ans: d

28. In a D.C. generator all of the following could be the effects of iron losses except……….

(a) Loss of efficiency

(b) Excessive heating of core

(c) Increase in terminal voltage

(d) Rise in temperature of ventilating air 

Ans: c

29. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator?

(a) hysteresis loss

(b) field copper loss

(c) armature copper loss
(d) eddy current loss

Ans: b                                                                                                                                                                       
 30. Which of the following loss in a D.C. generator varies significantly with the load current?
 (a)Field copper loss

(b) Windage loss

(c) Armature copper loss

(d) None of the above

Ans: c

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