D.C motor. Part – 1

1. The speed of D.C. shunt motor more than its full-load speed can be obtained by

A. Decreasing the field current

B. Increasing the field current

C. Decreasing the armature current

D. Increasing the armature current

2. Field winding of a DC series motor is usually provided with thick wire

A. To provide large flex

B. To reduce the use of insulation materials

C. As it carries large load current

D. In order to reduce eddy current

3. The best way to start a large DC shunt motor is with,

A. Weak field

B. Strong field

C. Full supply to the armature

D. Higher supply voltage

4. If the field circuit of a DC shunt motor opens during normal operation, the speed of motor will,

A. Increase

B. Decrease

C. Remain the same

D. Motor will stop

5. As the load is increased the speed of DC shunt motor will

A. Reduce rapidly

B. Increase slightly

C. Increase proportionately

D. Reduce slightly

6. A 230v dc motor has an armature circuit resistance of 0.6 ohm. If the full load armature current is 30A and the no load armature current is 4A, the change in back emf from no load to full load will be

A. 32.2V

B. 64V

C. 1.5V

D. 15.6V

7. Which DC motor is generally preferred for cranes and hoists?

A. DC shunt motor

B. Cumulatively compounded motor

C. DC series motor

D. Differentially compounded motor

8. Which motor should not be started on no-load?

A. DC shunt motor

B. DC series motor

C. Synchronous motor

D. induction motor

9. The commutator in D.C. Motor

A. Changing A.C. Into D.C.

B. Convert D.C. Into A.C.

C. Reducing friction

D. Avoiding arc at the brushes

10. When is mechanical power developed by DC motor maximum?

A. Back EMF is equal to applied voltage

B. Back EMF is zero

C. Back EMF is equal to half of applied voltage

D. None of the above