d c motors Mcqs
101. D.C. shunt motors are used for driving____________?
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A. machine tools

B. hoists

C. trains

D. cranes

102. The hysteresis loss in a D.C. machine least depends on____________?
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A. Volume and grade of iron

B. Rate of flow of ventilating air

C. Maximum value of flux density

D. Frequency of magnetic reversals

103. Which of the following method of speed control of D.C. machine will offer minimum efficiency ?
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A. Voltage control method

B. Armature control method

C. Field control method

D. All above methods

104. Which of the following motors is most suitable for signalling devices and many kinds of timers ?
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A. D.C. shunt motor

B. Induction motor

C. Reluctance motor

D. D.C. series motor

105. Three point starter can be used for______________?
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A. series motor only

B. shunt motor only

C. compound motor only

D. both shunt and compound motor
106. Sparking, is discouraged in a D.C. motor because_____________?
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A. it increases the input power con-sumption

B. commutator gets damaged

C. both A. and B.

D. none of the above

107. Which D.C. motor has got maximum self loading property?
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A. Differentially compounded motor

B. Cumulatively compounded motor

C. Series motor

D. Shunt motor

108. D.C. generators are normally designed for maximum efficiency around_____________?
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A. rated voltage

B. full-load

C. rated r.p.m.

D. all of the above

109. In variable speed motor___________?
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A. none of the above is correct

B. a stronger commutating field is needed at low speed than at high speed

C. same commutating field is needed at low speed than at high speed

D. a weaker commutating field is needed at low speed than at high speed
110. Ward-Leonard control is basically a____________?
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A. voltage control method

B. field control method

C. armature resistance control method

D. field divertor method

111. The ratio of starting torque to full-load torque is least in case of____________?
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A. shunt motors

B. none of the above

C. series motors

D. compound motors

112. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is______________?
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A. 0.5

B. 4

C. 1

D. 2

113. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because____________?
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A. flux is practically constant in D:C. shunt motors

B. back e.m.f. is equal to armature drop

C. flux is proportional to armature current

D. armature drop is negligible

114. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be_____________?
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A. differentially compounded

B. level compounded

C. cumulatively compounded

D. under compounded

115. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is______________?
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A. 2.36%

B. 6.77%

C. 8.84%

D. 4.76%
116. As -the load is increased the speed of D.C. shunt motor will____________?
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A. increase proportionately

B. remains unchanged

C. increase slightly

D. reduce slightly
117. Sparking at the commutator of a D.C. motor may result in____________?
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A. increased power consumption

B. all of the above

C. damage to commutator segments

D. damage to commutator insulation

118. Which of the following motors one will choose to drive the rotary compressor ?
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A. Synchronous motor

B. Universal motor

C. D.C. series motor

D. D.C. shunt motor

119. In which of the following applications D.C. series motor is invariably tried?
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A. Fan motor

B. Drive for a water pump

C. Motor operation in A.C. or D.C

D. Starter for a car
120. The starting resistance of a D.C. motor is generally_______________?
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A. around 500 Q

B. low

C. 1000 Q

D. infinitely large

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