DC Motor Objective Questions Answers

1. In an electric motor, the electromagnetic torque developed is

(a) in opposite direction to both load torque and frictional torque.
(b) in the same direction as the load torque but in opposite direction to frictional torque.
(c) in the same direction as the load torque and frictional torque.
(d) in the same direction as the frictional torque but in the opposite direction to the load torque.

SHOW ANSWER

2. The toque-speed characteristic of a dc shunt motor is

(a) a rectangular hyperbola.
(b) a drooping straight line.
(c) a parabola.
(d) none of the above.

SHOW ANSWER

3. The horse power obtained from the motor shaft is called the

(a) IHP.
(b) BHP.
(c) useful output.
(d) none of these.

SHOW ANSWER

4. 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 of the above.

SHOW ANSWER

5. The mechanical output available at the dc motor shaft is equal to

(a) electrical power input to motor.
(b) electrical power input less iron and friction losses.
(c) electrical power input less copper losses.
(d) electrical power input less total losses (copper loss, iron loss, friction and windage losses).

SHOW ANSWER

6. In a dc motor if the brushes are given a backward shift, then

(a) commutation is improved.
(b) commutation is worsened.
(c) speed increases.
(d) speed decreases.
(e) speed remains unaffected.
(f)both (a) and (c).

SHOW ANSWER

7. T and P are the developed electromagnetic torque and the shaft power of a dc series motor. If losses are neglected, then for constant terminal voltage

(a) T α P
(b) T α 1/P
(c) T α √P
(d) T α P2

SHOW ANSWER

8. Which of the following statements associated with a dc series motor is correct?

(a) It has poor torque.
(b) It gives almost constant speed.
(c) Its field winding consists of few turns of thick wire.
(d) It may run away if its field gets opened.
(e) It can be started on no load.

SHOW ANSWER

9. In comparison to shunt and compound motors, a dc series motor develops high torque at start. It is due to its comparatively

(a) few series turns.
(b) stronger series field.
(c) larger armature current.
(d) smaller armature resistance.

SHOW ANSWER

10. A flywheel is normally fitted to

(a) dc series motor driving a constant torque load.
(b) separately excited dc motor driving pulsed torque load.
(c) cumulatively compound motor driving torque load.
(d) differentially compound motor driving pulsed torque load.

SHOW ANSWER

11. An unsaturated dc shunt motor drives a constant torque load at a speed at 1000 rpm taking an armature current of 20 A when 230 V is applied to the motor. If the applied voltage is reduced to 115 V, the motor runs at

(a) 500 rpm taking an armature current of 20 A.
(b) 1000 rpm taking an armature current of 20 A.
(c) 500 rpm taking an armature current of 40 A.
(d) 1000 rpm taking an armature current of 40 A.

SHOW ANSWER

12. An electric motor with “constant output power” will have a torque-speed characteristic in the form of a

(a) straight line through the origin.
(b) straight-line parallel to speed axis.
(c) circle about the origin.
(d) rectangular hyperbola.

SHOW ANSWER

13. T is the load torque of a dc series motor having linear magnetization and negligible armature resistance. Speed of the motor is

(a) inversely proportional to √T.
(b) directly proportional to √T.
(c) inversely proportional to T2.
(d) directly proportional to T2.

SHOW ANSWER

14. 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

(a) drop in speed and rise in current.
(b) rise in speed and drop in current.
(c) rise in speed and rise in current.
(d) drop in speed with current unaltered.

SHOW ANSWER

15. In a dc series motor, if armature current is reduced to 70% of its original value, the torque of the motor will be reduced by

(a) 49%
(b) 51%
(c) 50%
(d) 70%

SHOW ANSWER

16. When the torque of a dc series motor is tripled, the power approximately increases by

(a) 33%
(b) 50%
(c) 75%
(d) 150%

SHOW ANSWER

17. When an electric train is moving down a hill, the dc motor will operate as a dc

(a) series motor.
(b) series generator.
(c) shunt motor.
(d) shunt generator.

SHOW ANSWER

18. A dc series motor must not be started on no load because it would

(a) not develop starting torque.
(b) fail to start without load.
(c) run at dangerously high speed.
(d) draw more current without producing sufficient torque.

SHOW ANSWER

19. In case of a dc series motor it is possible to have finite no-load speed if a resistance is connected across its

(a) field terminals.
(b) armature terminals.
(c) field and armature together.
(d) it is always very high at no-load.

SHOW ANSWER

20. It is advisable to start a dc series motor with some load to

(a) limit the flux.
(b) limit the current.
(c) limit the speed.
(d) avoid sparking.
(e) avoid demagnetization of field system.

SHOW ANSWER

21. The speed of a 4-pole dc series motor at no load will be

(a) zero.
(b) 3000 rpm.
(c) infinite.
(d) 1500 rpm.
(e) depending upon the applied voltage.

SHOW ANSWER

22. A dc series motor is best suited for driving

(a) line shafting, blowers and fans.
(b) machine tools.
(c) shear and punches.
(d) cranes and hoists.
(e) none of these.

SHOW ANSWER

23. DC series motor is best suited for electric traction as

(a) it develops high starting torque.
(b) it runs at very high speed at light load.
(r) it is cheaper in cost.
(d) it consumes less power.

SHOW ANSWER

24. A dc series motor is running at rated speed without any additional resistance in series. If an additional resistance is placed in series, the speed of motor

(a) increases.
(b) decreases.
(c) remains unchanged.
(d) oscillates around the rated speed.

SHOW ANSWER

25. A dc series motor is used for an overhauling load. It can work stably if

(a) the armature is shunted by a resistor.
(b) the field winding is reversed.
(c) a resistor is put in series with the machine.
(d) a divertor is put across the field.

SHOW ANSWER

26. A dc shunt motor is driving a constant torque load. On inserting an additional resistance in the armature circuit, the speed of the motor will

(a) remain unchanged.
(b) increase.
(c) decrease.
(d) be zero.

SHOW ANSWER

27. A dc shunt motor may have rising speed-torque characteristic due to

(a) very high armature circuit resistance.
(b) very high field circuit resistance.
(c) very high demagnetizing armature reaction.
(d) very low demagnetizing armature reaction.

SHOW ANSWER

28. Consider the following statements: If the terminal voltage of a dc shunt motor is halved with the load torque varying as the square of speed, then

  1. speed is halved.
  2. speed remains unaltered.
  3. armature current is doubled.
  4. armature current remains unaltered.

Of these statements
(a) 1 and 3 are correct.
(b) 1 and 4 are correct.
(c) 2 and 3 are correct.
(d) 2 and 4 are correct.

SHOW ANSWER

29. If the speed of a dc motor increases with load torque, then it is a

(a) series motor.
(b) permanent magnet motor.
(c) differentially compounded motor.
(d) cumulatively compounded motor.

SHOW ANSWER

30. A separately excited dc generator is feeding a dc shunt motor. If the load torque on the motor is halved approximately

(a) armature current of both motor and generator are halved.
(b) armature current of motor is halved and that of the generator, is unaltered.
(c) armature current of generator is halved and that of motor is unaltered.
(d) armature current of both motor and generator are unaltered.

SHOW ANSWER

DC Motor Objective Questions Answers

 

  1. DC Motor Quiz MCQ
  2. DC Motor Questions and Answers
  3. Electrical Machines Quiz MCQ Questions
  4. DC Motor Question Bank
  5. DC Generator MCQ Questions
  6. DC Generator Question and Answer with Solution
  7. DC Machines Questions and Answers
  8. DC Motor Questions and Answers
  9. DC Motor Objective Questions Answers
  10. DC Motor MCQ Question Answer
  11. DC Motor MCQ Questions
  12. DC Motor Multiple Choice Questions and Answers
  13. DC Motor MCQ Question and Answer
  14. DC Motor Objective Type Question Answer

© www.yourelectricalguide.com/ dc motor objective questions answers.

1 thought on “DC Motor Objective Questions Answers”

Leave a Comment

Your email address will not be published.