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Electrical Engineering Objective Questions { Induction Motors }

92. The rotor of an induction motor cannot run with synchronous speed because
A. Lenz's law would be violated
B. induction motor would then become synchronous motor
C. rotor torque would then become zero
D. air friction prevents it to do so
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93. When a load on a squirrel-cage induction motor is increased from no-load to full-load, which of the following statement is incorrect?
A. Slip increases
B. The magnetising component of the stator exiting current is increased
C. Stator power factor is improved
D. Torque developed by the motor increases till it equals the applied torque
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94. The power factor of an induction motor under no-load conditions is about
A. 0.2 lag
B. 0.4 lag
C. unity
D. 0.4 lead
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95.  If there is an open circuit in the rotor of a squirrel cage induction motor
A. rotor will overheat
B. line fuses will blow
C. motor will be noisy
D. motor will not start
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96.  The principle of operation of a 3-phase induction motor is most similar to that of
A. transformer with a shorted secondary
B. synchronous motor
C. capacitor-start induction run motor
D. repulsion-start induction motor
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97. The speed of a 3-phase would motor can be increased by
A. short-circuiting slip-rings
B. increasing applied voltage
C. decreasing applied voltage
D. decreasing external resistance in the rotor circuit
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98. The A.C. motor which would be best suited to drive a centrifugal pump for discharging a variable quantity of water against a Fixed head is the
A. repulsion motor
B. synchronous motor
C. squirrel cage
D. slip ring induction motor
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