Electrical Machines MCQ Questions and Answers for Practice

1. The power factor of the induction motor will be __________ if the magnetizing current is __________

1. Low......low
2. High........high
3. High.....low
4. Low ....... high

2. The magnetizing current of an induction motor will be __________ for __________ air gap

1. Larger .......... smaller
2. Larger ......... larger
3. Smaller....... larger
4. Smaller...........smaller

3. In induction motors, small air gap __________ power factor and __________ noise level

1. Increases .......... reduces
2. Reduces .......... increases
3. Reduces..........also reduces
4. Increases..........also increases

4. In induction motors, the difference between the number of stator and rotor slots should not be

1. P
2. 2P
3. 5P
4. Any of the above

5. Induction motor which of the following depends on the leakage reactance?

1. Starting torque
2. Maximum torque
3. Starting current
4. All of the above

6. The use of double squirrel cage winding on the rotor provides

1. Low noise
2. Reduced starting torque
3. A large starting torque
4. Higher efficiency

7. In induction motor if the number of rotor slots is equal to the stator slots then

1. The motor will run smoothly
2. The motor will mil at zero slip
3. The noise level will be low
4. The motor may refuse to start

8. In squirrel cage motors, skin effect occurs in

1. Stator winding
2. Rotor winding
3. Both (A) and (B) above
4. None of the above

9. A synchronous machine having large length of the air gap will have

1. Higher noise level
2. Smaller unbalanced magnetic pull
3. Lower limit of stability
4. Higher value of inherent regulation

10. Damper windings are provided in synchronous machines to

1. Damp out rotor oscillations
2. Reduce the over-voltages under abnormal conditions
3. Facilitate starting
4. All of the above

11. Which of the following motors has a high starting torque?

1. AC series motor
2. DC series motor
3. Induction motor
4. Synchronous motor

12. The starting winding of a single-phase motor is placed in

1. Rotor
2. Stator
3. Armature
4. Field

13. In a DC series motor increase in load current results in

1. Decrease in speed
2. Increase in speed
3. Better commutation
4. Increase in the back emf

14. Which DC motors has approximately constant speed?

1. Series motor
2. Shunt motor
3. Cumulatively compound motor
4. All of the above.

15. An electric machine will have high efficiency when

1. input/output ratio is low
2. Reactive power is more
3. kWh consumption is low
4. losses are low