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Free download in PDF Polyphase Induction Motors General Knowledge Multiple Choice Questions(MCQs) & Answers for competitive exams. These short objective type questions with answers are very important for Board exams as well as competitive exams. These short solved questions or quizzes are provided by Gkseries.
(1)
An induction motor is identical to
[A]
D.C. compound motor
[B]
D.C. series motor
[C]
synchronous motor
[D]
asynchronous motor
Answer: asynchronous motor
(2)
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
(3)
An induction motor with 1000 r.p.m. speed will have
[A]
8 poles
[B]
6 poles
[C]
4 poles
[D]
2 poles
(4)
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
Answer: directly proportional to slip
(5)
The term ‘cogging’ is associated with
[A]
three phase transformers
[B]
compound generators
[C]
D.C. series motors
[D]
induction motors
(6)
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
Answer: single phase motors
(7)
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
Answer: two parallel windings in rotor
(8)
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
(9)
The number of slip rings on a squirrel cage induction motor is usually
[A]
two
[B]
three
[C]
four
[D]
none
(10)
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%
(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
(12)
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
(13)
Slip rings are usually made of
[A]
copper
[B]
carbon
[C]
phospor bronze
[D]
aluminium
(14)
In case the air gap in an induction motor is increased
[A]
the magnetising current of the rotor will decrease
[B]
the power factor will decrease
[C]
speed of motor will increase
[D]
the windage losses will increase
Answer: the power factor will decrease
(15)
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
Answer: reduce magnetic hum
(16)
In medium sized induction motors, the slip is generally around
[A]
0.04%
[B]
0.4%
[C]
4%
[D]
14%
(17)
In an induction motor, no-load the slip is generally
[A]
less than 1%
[B]
1.5%
[C]
2%
[D]
4%
(18)
The shaft of an induction motor is made of
[A]
high speed steel
[B]
stainless steel
[C]
carbon steel
[D]
cast iron
(19)
The shaft of an induction motor is made of
[A]
stiff
[B]
flexible
[C]
hollow
[D]
any of the above
(20)
The frame of an induction motor is usually made of
[A]
silicon steel
[B]
cast iron
[C]
aluminium
[D]
bronze
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