1. A double squirrel-cage induction motor has

(a) two rotors moving in opposite direction
(b) two parallel windings in the stator
(c) two parallel windings in the rotor
(d) two series windings in the stator

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Answer. c

2. The starting torque of a squirrel-cage induction motor is

(a) low
(b) negligible
(c) same as the full-load torque
(d) slightly more than full-load torque

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Answer. a

3. The number of slip rings on a squirrel cage induction motor is usually

(a) two
(b) three
(c) four
(d) none

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Answer. d

4. The efficiency of an induction motor can be expected to be nearly

(a) 60 to 90%
(b) 80 to 90%
(c) 95 to 98%
(d) 99%

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Answer. b

5. If Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be

(a) Ns
(b) s.N
(c) (l-s)Ns
(d) (Ns-l)s

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Answer. c

6. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be

(a) 200 Hz
(b) 50 Hz
(c) 2 Hz

(d) 0.2 Hz

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Answer. c

7. Slip rings are usually made of

(a) copper
(b) carbon
(c) phosphor bronze
(d) aluminium

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Answer. c

8. In case the air gap in an induction motor is increased

(a) the magnetizing current of the rotor will decrease
(b) the power factor will decrease
(c) the speed of the motor will increase
(d) the windage losses will increase

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Answer. b

9. In squirrel cage induction motors, the rotor slots are usually given slight skew in order to

(a) reduce windage losses
(b) reduce eddy currents
(c) reduce accumulation of dirt and dust
(d) reduce magnetic hum

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Answer. d

10. In medium sized induction motors, the slip is generally around

(a) 0.04%
(b) 0.4%
(c) 4%
(d) 14%

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Answer. c

11. In an induction motor, no-load the slip is generally

(a) less than 1%
(b) 1.5%
(c) 2%
(d) 4%

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Answer. a

12. The shaft of an induction motor is made of

(a) High-speeded steel
(b) stainless steel
(c) carbon steel
(d) cast iron

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Answer. c

13. The shaft of an induction motor is made of

(a) stiff
(b) flexible
(c) hollow
(d) any of the above

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Answer. a

14. The frame of an induction motor is usually made of

(a) silicon steel
(b) cast iron
(c) aluminium
(d) bronze

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Answer. b

15. Which of the following component is usually fabricated out of silicon steel?

(a) Bearings
(b) Shaft
(c) Stator core
(d) None of the above

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Answer. c

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