DC MACHINES 5

 

DC MACHINES MCQ 5

1. Which of the following motors is used for rolling mills?
a) D.C. shunt motor
b) D.C. cumulative compound motor.
c) D.C. series motor.
d) D.C. differential compound motor.
ans. b

2. Armature reaction is attributed to
a) the effect of magnetic field setup by armature current.
b) the effect of magnetic field setup by field current.
c) copper loss in the armature.
d) the effect of magnetic field setup by back emf.
ans. a

3. What will happen if the supply terminals of dc shunt motor are interchanged?
a) Motor will stop.
b) Motor will run at its normal speed in the same direction as it was running .
c) The direction of rotation will reverse.
d) Motor will run at a speed lower than the normal speed in the same direction.
ans. b

4. When the electric train is moving down a hill the dc motor acts as
a) dc series motor
b) dc shunt motor
c) dc series generator
d) dc shunt generator
ans.c

5. Which of the following dc motors is suitable for high starting torque?
a) shunt motor
b) cumulative compound motor
c) series motor
d) compound motor.
ans. c

6. D.C. series motors are best suited for traction work because
a) torque is proportional to the square of armature current and speed is inversely proportional to torque.

b) torque is proportional to the square of armature current and speed is proportional to the torque.
c) torque and speed are proportional to square of armature current.
d) none of these
ans. a

7. A series motor is started without load. The effect is that
a) the torque increases rapidly
b) the speed increases rapidly
c) current drawn increases rapidly
d) the back emf decreases.
ans. b

8. The direction of rotation of a dc series motor can be reversed by interchanging
a) the supply terminals only
b) the field terminals only
c) the supply as well as field terminals
d) None of these.
ans. b

9. The motor used for intermittent, high torque load is
a) dc shunt motor
b) dc series motor
c) differential compound motor
d) cumulative compound motor
ans. d

10. If the field of a dc shunt motor is opened.
a) it will continue to run at its rated speed.
b) the speed of the motor will become very high
c) the motor will stop
d) the speed of motor will decrease.
ans. b

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