d c motors MCQs – Page 7

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

d c motors Mcqs
121. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens____________?
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A. this will make armature to take heavy current, possibly burning it

B. nothing will happen to motor

C. motor will come to stop

D. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

122. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of_____________?
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A. D.C. series motor

B. all of above motors

C. D.C. shunt motor

D. induction motor

123. If the load on a DC shunt motor is increases, its speed is slightly reduced due to______________?
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A. decrease in reactance

B. increase in armature current

C. decrease in back emf

D. increase in flux

124. The plugging gives the____________?
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A. smallest torque braking

B. zero torque braking

C. none of the above

D. highest torque braking
125. When the armature of a D.C. motor rotates, e.m.f. induced is___________?
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A. none of the above

B. back e.m.f

C. mutually induced e.m.f.

D. self-induced e.m.f.

126. The armature voltage control of D.C. motor provides____________?
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A. constant voltage drive

B. none of the above

C. constant current drive

D. constant torque drive
127. Which method of braking is generally used in elevators ?
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A. Rheostatic braking

B. Plugging

C. Regenerative braking

D. None of the above

128. In D.C. motor which of the following can sustain the maximum temperature rise?
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A. Field winding

B. Slip rings

C. Commutator

D. Armature winding

129. A three point starter is considered suitable for______________?
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A. shunt motors

B. shunt as well as compound motors

C. all D.C. motors

D. shunt, compound and series motors

130. Usually wide and sensitive speed control is desired in case of____________?
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A. steel rolling mills

B. elevators

C. centrifugal pumps

D. colliery winders
131. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven_______________?
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A. also runs as a motor comes to stop after sometime

B. does not run as a generator

C. runs as a generator