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Electrical Engineering Objective Questions { DC Motors }

190.  Sparking at the commutator of a D.C.will be
A. damage to commutator segments
B. damage to commutator insulation
C. increased power consumption
D. all of the above
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191.  If the supply voltage for a D.C. motor is increased, which of the following will decrease?
A. Starting torque
B. Operating speed
C. Full-load current
D. All of the above
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192.  As compared to an induction motor, the air gap in a D.C. motor is
A. less than 50%
B. between 50% and 90%
C. same control, the respective output
D. more powers delivered by the motor are
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193.  The mechanical power developed by a approximately.shunt motor will be maximum when the ratio of back e.m.f. of applied voltage is
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194.  The condition for maximum power in case of D.C. motor is
A. back e.m.f. = 2 x supply voltage
B. back e.m.f. = ?2 x supply voltage
C. supply voltage =-2 x back e.m.f.
D. supply voltage = back e.m.f.
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195.  For which of the following applications a D.C. motor is preferred over an A.C. motor?
A. Law speed operation
B. High speed operation
C. Variable speed operation
D. Fixed speed operation
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196.  In D.C. machines the residual magnetism is of the order of
A. 2 to 3 per cent
B. 10 to 15 per cent
C. 20 to 25 per cent
D. 50 to 75 per cent
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