TOP Polyphase Induction Motors Multiple choice Questions and Answers pdf

11.    In 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
Ans: c

 12.  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%
Ans: b

13.    The number of slip rings on a squirrel cage induction motor is usually
(a) two
(b) three
(c) four
(d) none
Ans: d

14.    The starting torque of a squirrel-cage induction motor is
(a)     low
(b)     negligible
(c)    same as full-load torque
(d)    slightly more than full-load torque
Ans: a

15.    A double squirrel-cage induction motor has
(a)     two rotors moving in oppsite direction
(b)     two parallel windings in stator
(c)    two parallel windings in rotor
(d)    two series windings in stator
Ans: c

16.    Star-delta starting of motors is not possible in case of
(a)     single phase motors
(b)     variable speed motors
(c)    low horse power motors
(d)    high speed motors
Ans: a

17.    The term 'cogging' is associated with
(a)     three phase transformers
(b)     compound generators
(c)    D.C. series motors
(d)    induction motors
Ans: d

18.    In case of the induction motors the torque is
(a)     inversely proportional to (Vslip)
(b)     directly proportional to (slip)2
(c)    inversely proportional to slip
(d)    directly proportional to slip
Ans: d

19.    An induction motor with 1000 r.p.m. speed will have
(a) 8 poles
(b) 6 poles
(c) 4 poles
(d) 2 poles
Ans: b

20.    The good power factor of an induction motor can be achieved if the average flux density in the air gap is
(a) absent
(b) small
(c) large
(d) infinity
Ans: b

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