Polyphase Induction Motors Mcqs - Set 5

1)   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  Explanation 

ANSWER: directly proportional to slip

Explanation:
No explanation is available for this question!


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  Explanation 

ANSWER: small

Explanation:
No explanation is available for this question!


3)   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  Explanation 

ANSWER: two parallel windings in rotor

Explanation:
No explanation is available for this question!


4)   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  Explanation 

ANSWER: single phase motors

Explanation:
No explanation is available for this question!


5)   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  Explanation 

ANSWER: low

Explanation:
No explanation is available for this question!


6)   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  Explanation 

ANSWER: (l-s)Ns

Explanation:
No explanation is available for this question!


7)   Slip rings are usually made of___________?

a. copper
b. carbon
c. phospor bronze
d. aluminium
Answer  Explanation 

ANSWER: phospor bronze

Explanation:
No explanation is available for this question!


8)   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  Explanation 

ANSWER: the power factor will decrease

Explanation:
No explanation is available for this question!


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
Answer  Explanation 

ANSWER: reduce magnetic hum

Explanation:
No explanation is available for this question!


10)   In medium sized induction motors, the slip is generally around___________?

a. 0.04%
b. 0.4%
c. 4%
d. 14%
Answer  Explanation 

ANSWER: 4%

Explanation:
No explanation is available for this question!


11)   Which of the following component is usually fabricated out of silicon steel ?

a. Bearings
b. Shaft
c. Statorcore
d. None of the above
Answer  Explanation 

ANSWER: Statorcore

Explanation:
No explanation is available for this question!


12)   An induction motor with 1000 r.p.m. speed will have____________?

a. 8 poles
b. 6 poles
c. 4 poles
d. 2 poles
Answer  Explanation 

ANSWER: 6 poles

Explanation:
No explanation is available for this question!


13)   The term ‘cogging’ is associated with___________?

a. three phase transformers
b. compound generators
c. D.C. series motors
d. induction motors
Answer  Explanation 

ANSWER: induction motors

Explanation:
No explanation is available for this question!


14)   The number of slip rings on a squirrel cage induction motor is usually____________?

a. two
b. three
c. four
d. none
Answer  Explanation 

ANSWER: none

Explanation:
No explanation is available for this question!


15)   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  Explanation 

ANSWER: 80 to 90%

Explanation:
No explanation is available for this question!


16)   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  Explanation 

ANSWER: 2 Hz

Explanation:
No explanation is available for this question!


17)   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  Explanation 

ANSWER: the power factor will decrease

Explanation:
No explanation is available for this question!


18)   In an induction motor, no-load the slip is generally____________?

a. less than 1%
b. 1.5%
c. 2%
d. 4%
Answer  Explanation 

ANSWER: less than 1%

Explanation:
No explanation is available for this question!


19)   The shaft of an induction motor is made of_____________?

a. high speed steel
b. stainless steel
c. carbon steel
d. cast iron
Answer  Explanation 

ANSWER: carbon steel

Explanation:
No explanation is available for this question!


20)   The torque of an induction motor is___________?

a. directly proportional to slip
b. inversely proportional to slip
c. proportional to the square of the slip
d. none of the above
Answer  Explanation 

ANSWER: directly proportional to slip

Explanation:
No explanation is available for this question!


21)   The frame of an induction motor is usually made of____________?

a. silicon steel
b. cast iron
c. aluminium
d. bronze
Answer  Explanation 

ANSWER: cast iron

Explanation:
No explanation is available for this question!