DC Motors Questions and Answers in Quiz Form 8 for Practice

106. In D.C. motor which of the following can sustain the maximum temperature rise?

1. Slip rings
2. Commutator
3. Field winding
4. Armature winding

107. 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

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

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

109. 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

110. 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

111. 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.

112. 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

113. 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

114. 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

115. 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

116. 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

117. Speed control by Ward Leonard method gives uniform speed variation

1. in one direction
2. in both directions
3. below normal speed only
4. above normal speed only.

118. Starters are used with D.C. motors because

1. these motors have high starting torque
2. these motors are not self-starting
3. back e.m.f. of these motors is zero initially
4. to restrict armature current as there is no back e.m.f. while starting

119. The armature torque of the D.C. shunt motor is proportional to

1. field flux only
2. armature current only
3. both a and b
4. none of the above

120. The armature voltage control of D.C. motor provides

1. constant torque drive
2. constant voltage drive
3. constant current drive
4. none of the above