d c motors MCQs – Page 5

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

d c motors Mcqs
81. Which of the following motor has the poorest speed regulation ?
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A. Shunt motor

B. Differential compound motor

C. Cumulative compound motor

D. Series motor
82. During rheostat braking of D.C. series motors_____________?
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A. motor is run at reduced speed

B. motor is reversed in direction

C. motor is run as a generator
83. If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
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A. Starting torque

B. Full-load current

C. Operating speed

D. All of the above

84. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the________________?
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A. shunt motor

B. compound motor

C. any of the above

D. series motor
85. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
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A. Eddy current losses

B. Copper losses

C. Windage losses

D. Hysteresis losses

86. Which of the following loss in a D.C. generator varies significantly with the load current ?
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A. Windage loss

B. None of the above

C. Armature copper loss

D. Field copper loss

87. Which of the following method is used for the speed control of DC shunt motor?
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A. all of the above

B. rheostat control method

C. flux control method

D. voltage control method

88. 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 ?
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A. armature copper loss

B. field copper loss

C. hysteresis loss

D. eddy current loss

89. In a differentially compounded D.C. motor, if shunt field suddenly opens____________?
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A. the motor will work as series motor and run at slow speed in the same direction

B. the motor will not work and come to stop

C. the motor will work as series motor and run at high speed in the same direction

D. the motor will first stop and then run in opposite direction as series motor
90. In which of the following device the generated emf and armature current are in the opposite directions?
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A. dc generator

B. all of the above

C. dc motor

D. transformer

91. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking?
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A. any of the above

B. plugging

C. dynamic braking

D. none of the above

E. regenerative

92. Following motor is used where high starting torque and wide speed range control is required?
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A. None of the above

B. Induction motor

C. Synchronous motor

D. Single phase capacitor start

E. D.C. motor
93. Why are the D.C. motors preferred for traction applications ?
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A. The speed is inversely proportional to the torque and the torque is proportional to square of armature current

B. Torque is proportional to armature current

C. Torque and speed are inversely proportional to armature current

D. Torque is proportional to square root of armature current

94. The armature voltage control of D.C. motor provides_____________?
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A. constant torque drive

B. constant voltage drive

C. none of the above

D. constant current drive

95. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
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A. The armature may burn

B. The motor will stop

C. The motor will run noisy

D. The motor will continue to run

96. D.C. generators are installed near the load centres to reduce_____________?
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A. sparking

B. corona losses

C. line losses

D. iron losses

97. The speed of a D.C. shunt motor can be increased by_______________?
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A. reducing the resistance in the armature circuit

B. reducing the resistance in the field circuit

C. increasing the resistance in field circuit

D. increasing the resistance in armature circuit

98. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this______________?
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A. any of the above

B. compound motor

C. shunt motor

D. series motor

99. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
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A. Frame

B. Commutator

C. Stator

D. Shaft

100. The condition for maximum efficiency for a D.C. generator is______________?
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A. copper losses = 0

B. variable losses = constant losses

C. hysteresis losses = eddy current losses

D. eddy current losses = stray losses