131. Which of the following statements associated with a dc series motor is correct?
- it has poor torque
- it gives almost constant speed
- its field winding consists of few turns of thick wire
- it may run away if its field gets opened
132. An electric motor with “constant output power” will have a torque speed characteristic in the form of a
- straight line through the origin
- straight line parallel to speed axis
- circle about the origin
- rectangular hyperbola
133. An electric train employing a dc series motor is running at a fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in
- drop in speed and rise in current
- rise in speed and drop in current
- rise in speed and rise in current
- drop in speed with current unaltered
134. In the dc series motor, if armature current is reduced to 70% of its original value, the torque of the motor will be reduced by
- 49%
- 51%
- 50%
- 70%
135. When the torque of a dc series motor is trippled, the power approximately increases by
- 33%
- 50%
- 75%
- 150%
136. When an electric train is moving down a hill, the dc motor will operate as a dc
- series motor
- series generator
- shunt motor
- shunt generator
137. A dc series motor must not be started on no load because it would
- not develop starting torque
- fail to start without load
- run at dangerously high speed
- draw more current without producing sufficient torque
138. In case of a dc series motor it is possible to have finite no-load speed if a resistance is connected across its
- field terminals
- armature terminals
- field and armature together
- it is always very high at no-load
139. It is advisable to start a dc series motor with some load to
- limit the flux
- limit the current
- limit the speed
- avoid sparking
140. The speed of a 4-pole dc series motor at no load will be
- zero
- 3000 rpm
- infinite
- 1500 rpm
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