d c motors MCQs – Page 3

Practise focused d c motors questions with marked answers for exam preparation and subject revision.

d c motors Mcqs

41. The total losses in a well designed D.C. generator of 10 kW will be nearly______________?
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A. 500 W

B. 1000 W

C. 1500 W

D. 100 W

42. Which of the following motor is preferred for operation in highly explosive atmosphere ?
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A. Series motor

B. Shunt motor

C. Air motor

D. Battery operated motor

43. Which of the following motors is usually used in house-hold refrigerators ?
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A. Reluctance motor

B. D.C. series motor

C. D.C. shunt motor

D. Single phase induction motor (split phase start or induction run motor)

E. Synchronous motor

44. Speed control by Ward Leonard method gives uniform speed variation_____________?
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A. in one direction

B. in both directions

C. below normal speed only

D. above normal speed only

45. In Ward-Leonard control the lower limit of speed is imposed by________?
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A. mechanical losses of motor and generator together

B. residual magnetism of the generator

C. all of the above

D. core losses of motor

46. Which of the following load normally needs starting torque more than the rated torque?
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A. Air compressors

B. Centrifugal pumps

C. Conveyors

D. Blowers

47. In a D.C. generator, the iron losses mainly take place in___________/
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A. armature conductors

B. armature rotor

C. commutator

D. yoke

48. The speed of a D.C. shunt motor more than its full-load speed can be obtained by_____________?
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A. increasing the field current

B. increasing the armature current

C. decreasing the field current

D. decreasing the armature current

49. Which motor has the poorest speed control?
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A. Differentially compounded motor

B. Cumulatively compounded motor

C. Shunt motor

D. Series motor

50. With the increase in temperature, the speed of DC series motor______________?
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A. decreases

B. remain same

C. none of the above

D. increases

51. Armature reaction in dc motor results___________?
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A. open circuit

B. decrease in speed

C. short circuit

D. increase in speed

52. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
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A. Using non-magnetic material for frame

B. Using material of low hysteresis co-efficient for armature core material

C. Providing laminations in stator

D. Providing laminations in armature core

53. For a D.C. shunt motor if the excitation is changed_______________?
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A. torque will remain constant

B. torque will change but power will remain constant

C. torque and power both will change

D. torque, power and speed, all will change

54. The current drawn by the armature of D.C. motor is directly proportional to__________?
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A. the voltage across the terminals

B. the torque required

C. the speed of the motor

D. none of the above

55. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens__________?
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A. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed

B. this will make armature to take heavy current, possibly burning it

C. nothing will happen to the motor

56. A direct on line starter is used: for starting motors___________?
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A. up to 20 H.P

B. up to 15 H.P

C. up to 5 H.P

D. up to 10 H.P

57. In the D.C. motor the iron losses occur in____________?
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A. the brushes

B. the armature

C. the field

D. the commutator

58. Which motor should not be started on no-load ?
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A. Cumulatively compounded motor

B. Series motor

C. Shunt motor

D. Differentially compounded motor

59. If I2 be the armature current, then speed of a D.C. shunt motor is_______________?
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A. varies as (Ia)

B. proportional to la

C. independent of Ia

D. varies as la

60. Which D.C. motor has got maximum self relieving property ?
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A. Series motor

B. Shunt motor

C. Cumulatively compounded motor

D. Differentially compounded motor

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