MULTIPLE CHOICE QUESTIONS
Q.1 Regarding skewing of motor bars in a squirrel cage induction motor, (SCIM) which statement is false ?
(A) it prevents cogging
(B) it increases starting torque
(C) it produces more uniform torque
(D) it reduces motor ‘hum’ during its operation.
Q.2 The principle of operation of a 3-phase. Induction motor is most similar to that of a
(A) synchronous motor
(B) repulsion-start induction motor
(C) transformer with a shorted secondary
(D) capacitor-start, induction-run motor.
Q.3 The magnetising current drawn by transformers and induction motors is the cause of their
.........power factor.
(A) zero
(B) unity
(C) lagging
(D) leading.
Q.4 The effect of increasing the length of air-gap in an induction motor will be to increase the
(A) power factor
(B) speed
(C) magnetising current
(D) air-gap flux.
Q.5 In a 3-phase induction motor, the relative speed of stator flux with respect to ..........is zero.
(A) stator winding
(B) rotor
(C) rotor flux
(D) space.
Q.6 An eight-pole wound rotor induction motor operating on 60 Hz supply is driven at 1800 r.p.m. by a prime mover in the opposite direction of revolving magnetic field. The frequency of rotor current is
(A) 60 Hz
(B) 120 Hz
(C) 180 Hz
(D) none of the above.
Q.7 A 3-phase, 4-pole, 50-Hz induction motor runs at a speed of 1440 r.p.m. The rotating field
produced by the rotor rotates at a speed of ....... r.p.m... with respect to the rotor.
(A) 1500
(B) 1440
(C) 60
(D) 0.
Q.8 In a 3-f induction motor, the rotor field rotates at synchronous speed with respect to
(A) stator
(B) rotor
(C) stator flux
(D) none of the above.
Q.9 Irrespective of the supply frequency, the torque developed by a SCIM is the same whenever ........ is the same.
(A) supply voltage
(B) external load
(C) rotor resistance
(D) slip speed.
Q.10 In the case of a 3 phase induction motor having Ns = 1500 rpm and running with s = 0.04
(A) revolving speed of the stator flux is space is .....rpm
(B) rotor speed is ........rpm
(C) speed of rotor flux relative to the rotor is .......rpm
(D) speed of the rotor flux with respect to the stator is ........rpm.
