Polyphase Induction Motors General Knowledge Quiz | Polyphase Induction Motors General Knowledge Multiple Choice Questions(MCQs) & Answers

Questions
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

Answer: small
3 An induction motor with 1000 r.p.m. speed will have
A 8 poles
B 6 poles
C 4 poles
D 2 poles

Answer: 6 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

Answer: 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

Answer: low
9 The number of slip rings on a squirrel cage induction motor is usually
A two
B three
C four
D none

Answer: 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%

Answer: 80 to 90%
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

Answer: (l-s)Ns
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

Answer: 2 Hz
13 Slip rings are usually made of
A copper
B carbon
C phospor bronze
D aluminium

Answer: phospor bronze
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%

Answer: 4%
17 In an induction motor, no-load the slip is generally
A less than 1%
B 1.5%
C 2%
D 4%

Answer: less than 1%
18 The shaft of an induction motor is made of
A high speed steel
B stainless steel
C carbon steel
D cast iron

Answer: carbon steel
19 The shaft of an induction motor is made of
A stiff
B flexible
C hollow
D any of the above

Answer: stiff
20 The frame of an induction motor is usually made of
A silicon steel
B cast iron
C aluminium
D bronze

Answer: cast iron
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