DC Machines Objective Questions Answers

1. Torque development in a dc motor depends on:

a) Magnetic field and radius of armature

b) Current flowing through the armature conductors

c) Active length of the conductors and number of armature conductors

d) All the above

D

2. The horse power obtained from the motor shaft is called:

a) IHP

b) BHP

c) Useful torque

d) None of the above

C

3. The efficiency of a dc motor when developing maximum power will be about:

a) 100%

b) 50%

c) Less than 50%

d) More than 50%

C

4. A dc motor having full load speed of 75 rpm and speed regulation of 10% will have no load speed of:

a) 825 rpm

b) 675 rpm

c) 800 rom

d) 700 rpm

A

5. The direction of rotation of a dc compound motor can be reversed by interchanging __ connections:

a) Armature

b) Series field

c) Shunt field

d) Armature and series field

A

6. A DC shunt motor is running at light load, what happens if the field winding gets opened?

a) Motor will stop

b) Motor will burn

c) Motor will make noise

d) Motor will pickup high speed 

D

7. In an electrical motor, the electromagnetic torque developed is:

a) In opposite direction to both load torque and fractional torque

b) In the same direction to the load torque but opposite direction to the fractional torque

c) In the same direction as the load torque and fractional torque

d) In the same direction as the fractional torque but in opposite direction to the load torque

A

8. In a dc motor, the shaft torque is less than armature torque . This is due to:

a) Eddy current loss

b) Hysteresis loss

c) Stray loss

d) All the above 

C

9. The starting torque of dc shunt motor is:

a) Zero

b) Low

c) High

d) Very high

B

10. A DC shunt motor may have rising speed-torque characteristics due to:

a) Very high armature circuit resistance

b) Very high field circuit resistance

c) Very high demagnetizing armature resistance

d) Very low demagnetizing armature reaction

C

11. The dc motor, that has poorest speed regulation is:

a) Cumulative compound

b) Differential compound

c) Series

d) Shunt

B

12. The dc motor that draws almost same power at different loads is:

a) Cumulative compound

b) Differential compound

c) Series

d) Shunt

C

13. If the supply voltage to a dc shunt motor is increased by 15%, which of the following will reduce?

a) Full load current

b) Full load speed

c) Starting torque

d) None of the above

A

14. When the torque of dc series motor is tripled, the power approximately increases by:

a) 33%

b) 50%

c) 75%

d) 150%

C

15. The speed of dc shunt motor can be increased above its normal speed by:

a) Increasing the field current

b) Decreasing the field current

c) Decreasing the terminal voltage

d) Increasing the armature resistance

B