1. The main function of using starter in induction motor is to
(a) avoid starting torque.
(b) reduce starting torque.
(c) avoid starting current.
(d) reduce starting current.
Answer
2. The slip of a squirrel cage induction motor is small due to
(a) high resistance of rotor winding.
(b) low resistance of rotor winding.
(c) high reactance of rotor winding.
(d) low reactance of rotor winding.
Answer
3. The emf induced in the rotor of an induction motor at synchronous speed is
(a) equal to supply voltage.
(b) zero.
(c) slip time of supply voltage.
(d) maximum.
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4. If the value of rotor resistance of a 3-phase induction motor is increased then the value of slip at which maximum torque occur will
(a) remain same.
(b) increase.
(c) decrease.
(d) data insufficient.
Answer
5. In an 3 phase induction motor, the frequency of rotor current of emf is
(a) zero.
(b) greater then supply frequency.
(c) equal to supply frequency.
(d) slip times of supply frequency.
Answer
6. The rotor speed of 3 phase induction motors is
(a) equal to synchronous speed.
(b) more then synchronous speed.
(c) less then synchronous speed.
(d) slip times of synchronous speed.
Answer
7. The slip ring induction motors are employed only when we require
(a) speed control.
(b) high starting torque.
(c) constant speed.
(d) speed control or high starting torque.
Answer
8. The slots on rotor of induction motor are usually skewed in order to
(a) reduce copper losses.
(b) reduce iron losses.
(c) obtain a more uniform torque.
(d) all of the above.
Answer
9. As load on an induction motor goes on increasing its power factor
(a) goes on decreasing.
(b) goes on increasing even after full load.
(c) remains constant.
(d) goes on increasing up to full load and then it falls again.
Answer
10. In case of a double cage induction motor, the inner cage has
(a) high inductance and low resistance.
(b) low inductance and high resistance.
(c) low inductance and low resistance.
(d) high inductance and high resistance.
Answer
11. The starting torque of any single phase induction motor is
(a) high.
(b) moderate.
(c) low.
(d) zero.
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12. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move
(a) in the opposite direction as the direction of the rotating field.
(b) in the same direction as the direction of the field.
(c) in any direction depending upon phase squence of supply.
(d) motor will not start.
Answer
13. Short-circuit test on an induction motor cannot be used to determine
(a) windage losses.
(b) copper losses.
(c) transformation ratio.
(d) power scale of circle diagram.
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14. If air gap in an induction motor is increased, it power factor will
(a) remain same.
(b) decrease.
(c) increase.
(d) none of these.
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15. In induction motor, percentage slip depends on
(a) power factor.
(b) supply frequency.
(c) supply voltage.
(d) copper losses in motor.
Answer