DC Motors MCQ Quiz - Multiple Choice Questions & Answers Page 6

51. In D.C. shunt motors as load is reduced

1. the speed will increase abruptly
2. the speed will increase in proportion to reduction in load
3. the speed will remain almost/constant
4. the speed will reduce

52. In the D.C. motor the iron losses occur in

1. the field
2. the armature
3. the brushes
4. the commutator

53. In variable speed motor

1. a stronger commutating field is needed at low speed than at high speed
2. a weaker commutating field is needed at low speed than at high speed
3. same commutating field is needed at low speed than at high speed
4. none of the above is correct

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

1. residual magnetism of the generator
2. core losses of motor
3. mechanical losses of motor and gen¬erator together
4. all of the above

55. In which of the following applications D.C. series motor is invariably tried?

1. Starter for a car
2. Drive for a water pump
3. Fan motor
4. Motor operation in A.C. or D.C.

56. No-load speed of which of the following motor will be highest ?

1. Shunt motor
2. Series motor
3. Cumulative compound motor
4. Differentiate compound motor

57. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven

1. runs as a generator
2. does not run as a generator
3. also runs as a motor comes to stop after sometime

58. Regenerative method of braking is based on that

1. back e.m.f. is less than the applied voltage
2. back e.m.f. is equal to the applied voltage
3. back e.m.f. of rotor is more than the applied voltage
4. none of the above

59. Sparking at the commutator of a D.C. motor may result in

1. damage to commutator segments
2. damage to commutator insulation
3. increased power consumption
4. all of the above

60. Sparking, is discouraged in a D.C. motor because

1. it increases the input power con-sumption
2. commutator gets damaged
3. both a and b
4. none of the above