21. A 3-phase induction motor

- is self-starting with zero torque
- is self-starting with high torque
- is self-starting with low torque
- is not self-starting

22. To use an AC motor in a DC circuit, Which equipment would be required additionally?

- Capacitor
- Inductor
- Inverter
- Rectifier

23. Rotating magnetic field is produced in a

- Single-phase induction motor
- Three-phase induction motor
- D.C. series motor
- A.C. series motor

24. The output power of any electric motor is taken from

- frame
- commutator
- coupling mounted on shaft
- armature

25. The rotor power output of a 3 phase induction motor is 15 kW and the corresponding slip is 4%. The rotor copper losses will be

- 525 W
- 625 W
- 600 W
- 500 W

26. If the rotor circuit resistance of a 3-phase induction motor is increased, then

- The starting torque will increase but the maximum torque will remain unchanged
- Both the starting and the maximum torque will decrease
- The starting torque will decrease but the maximum torque will remain unchanged
- Both the starting and the maximum torque will increase

27. In the circle diagram for a 3 phase induction motor, the diameter of the circle is determined by?

- Rotor current
- Rotor current referred to stator
- Exciting current
- Total stator current

28. Which of the following motors can be used for unity power factor?

- Schrage motor
- Hysteresis motor
- Shaded pole motor
- Capacitor run motor

29. Motor operating at maximum power output has an efficiency of approximately

- 26.5 %
- 50 %
- 43 %
- 71 %

30. Slip of a 3 phase induction motor is 0.1. If the line frequency is 60 Hz, the rotor frequency will be

- 59.4 Hz
- 54 Hz
- 6 Hz
- 5.4 Hz