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Electrical Engineering Objective Questions { Induction Motors }

106. In a induction motor if P is the power delivered to a rotor and s is the slip, then the power lost in the rotor as copper loss will be
A. P/s
B. sP
C. s213
D. P/s2
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107.  The frame of an induction motor is made of
A. carbon
B. closed grained cast iron
C. aluminium
D. stainless steel
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108. Slip rings for induction motors are made of
A. phosphor bronze
B.(a) aluminium
C. carbon
D. cobalt steel
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109.  If s is the slip and f is the supply frequency, the frequency of rotor current is given by
A. s.f
B. s2f
C. s.f12
D. f/s
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110.  Which of the following statements is correct about an induction motor?
A. It is salf starting with high torque
B. It is self starting with zero torque
C. It is self starting with small torque as compared to rated torque
D. None of the above
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111. Type of bearing used for 25 H.P. motor is
A. roller bearing
B. bush bearing
C. needle bearing
D. ball bearing
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112.  When an induction motor is switched on the rotor frequency is
A. zero
B. 60 Hz
C. same as slip frequency
D. same as supply frequency
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