d c motors MCQs – Page 4

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

d c motors Mcqs
61. In a manual shunt motor starter?
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A. over load relay is connected in series and no volt relay in parallel with the load

B. over load relay is connected in parallel and no volt relay in series with the load

C. over load relay and no volt relay are both connected in series with the load

D. over load relay and no volt relay are both connected in parallel with the load

62. The purpose of retardation test on D.C. shunt machines is to find out____________?
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A. eddy current losses

B. stray losses

C. field copper losses

D. windage losses

63. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control______________?
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A. four point starter is used

B. three point starter is used

C. drum type controller is used

D. all above can be used

64. With the increase in temperature, the speed of DC shunt motor____________?
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A. decreases.

B. remain same

C. increases

D. none of the above

65. For which types of D.C. motor, dynamic braking is generally used ?
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A. Shunt motors

B. All of the above

C. Compound motors

D. Series motors

66. Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
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A. Coloumbs law

B. Lenzs law

C. Faradays law

D. Flemings left-hand rule
67. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit____________________?
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A. a resistance is connected parallel to the armature

B. a high value resistor is connected across the field winding

C. a resistance is connected in series with armature

D. armature is temporarily open circuited

68. In a D.C. generator all of the following could be the effects of iron losses except___________?
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A. Loss of efficiency

B. Rise in temperature of ventilating air

C. Increase in terminal voltage

D. Excessive heating of core

69. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by______________?
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A. increasing the excitation current

B. none of the above methods

C. reducing the field current

D. decreasing the armature current

E. increasing the armature current

70. For constant torque drive which speed control method is preferred ?
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A. Field control

B. Shunt armature control

C. Mechanical loading system

D. Armature voltage control
71. For the same H.P. rating and full load speed, following motor has poor starting torque_____________?
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A. differentially compounded

B. series

C. shunt

D. cumulativelycompounded

72. Which D.C. motor will be suitable along with flywheel for intermittent light and heavy loads?
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A. Shunt motor

B. Series motor

C. Cumulatively compounded motor

D. Differentially compounded motor

73. Ward Leonard method of speed control is basically a______________?
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A. frequency control method

B. armature controlled method

C. field control method

D. field diverter

74. The power mentioned on the name plate of an electric motor indicates____________?
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A. the gross power

B. the power drawn in kW

C. the power drawn in kVA

D. the output power available at the shaft
75. These days D.C. motors are widely used in____________?
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A. electric traction

B. machine shops

C. pumping sets

D. air compressors

76. In a D.C. shunt motor, speed is______________?
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A. independent of armature current

B. directly proportional to the armature current

C. inversely proportional to the armature current

D. proportional to the square of the current

77. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will_________?
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A. become zero

B. remain same

C. decrease

D. increase
78. In case of conductively compensated D.C. series motors, the compensating winding is provided______________?
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A. as separately wound unit

B. in parallel with armature winding

C. in parallel with field winding

D. in series with armature winding
79. In D.C. machines fractional pitch winding is used__________?
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A. to reduce the sparking

B. to increase the generated e.m.f.

C. to reduce copper losses

D. to improve cooling

80. The condition for maximum power in case of D.C. motor is______________?
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A. supply voltage = back e.m.f

B. back e.m.f. = 2 x supply voltage

C. back e.m.f. = | x supply voltage

D. supply voltage = | x back e.m.f