Electrical Machines MCQs Quiz Multiple Choice Questions & Answers

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

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

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

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

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

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

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

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

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

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

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

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

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

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

8. In squirrel cage motors, skin effect occurs in

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

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

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

10. Damper windings are provided in synchronous machines to

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

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

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

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

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

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

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

14. Which DC motors has approximately constant speed?

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

15. An electric machine will have high efficiency when

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

16. Inter poles in DC machines are provided to reduce

1. Armature reaction
2. Iron loss
3. Efficiency
4. Sparking

17. DC motor yoke is generally made of

1. Copper
2. Aluminum
3. Steel
4. Wood

18. The output of a rotating electrical machine is limited by

1. Peripheral velocity
2. Temperature rise
3. None of the above
4. Size of the machine

19. The dimensions of a dc machine primarily depend on

1. Work done per revolution
2. Exposed surface
3. None of the above
4. kW output

20. Skewing of rotor slots helps in

1. Reducing noise
2. Suppressing undesirable harmonics
3. all of the above
4. Improving beat transfer

21. The harmonics in rotating machines are generated due to

1. Slotting of the stator core
2. Both (A) and (B) above
3. None of the above
4. Non-sinusoidal field form

22. The effect of harmonics in rotating machines can be minimized by

1. Skewing the poles
2. Use of distributed winding
3. all of the above
4. Use of longer air gap

23. In dc machines the number of poles is generally decided by

1. Weight of iron parts
2. Weight of copper
3. all of the above
4. Frequency of flux reversals

24. In dc machines by increasing the number of poles, all of the following reduce except:

1. Weight of iron parts
2. Frequency of flux reversals
3. Overall size of the machine
4. Weight of copper