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- The back EMF in DC motor ……
Opposes the applied voltage
Aids the applied voltage
Aids the armature current
Provide the fine speed
- A DC motor takes a large current at starting
because ……..
The armature resistance is high
Back emf is low
Shunt field is producing weak field
Dirt on commutator
- Commutating poles are also known as ….
Main pole
Primary pole
Interpol
Pole Pitch
- A series motor will over speed when ……..
The load is increases
The field is open
The armature circuit is open
The load is removed
- The shaft torque in a DC motor is less than
total armature torque because of …… in the
motor
Cu loss Field loss
Iron and friction loss
Bearing loss only
- The resistance of shunt field winding as
compared to series field winding is ….
Less
More
Same
Double
- A 20 HP DC motor has 89.03% efficiency
at rated power. What are its total losses
1787 W
1232 W
2184 W
1572 W
- The current drawn by a 220 V dc motor of
armature resistance 0.5 ohm and back emf
200 V is …..
44 A
40 A
400 A
440 A
- The friction and windage loss in a DC
motor depends upon …..
Speed
Flux
Armature current
Field and armature resistance
- DC series motors are used in those
applications where ………. Is required
High starting torque
Constant speed
Low no load speed
Low starting torque
- ……. The motor is most suitable for punch
press
Shunt
Series
Differential compound
Cumulative compound
- Which motor is not be used for centrifugal
pumps
Shunt
Series
Cumulative compound
Differential compound
- The most commonly used method of
speed control of DC motor is by varying
…..
The voltage applied to the motor
Field strength
The effective number of a conductor in series
Armature circuit resistance