731. Sparking at the commutator of a D.C. motor may result in____________?
A. damage to commutator segments
B. damage to commutator insulation
C. increased power consumption
D. all of the above
732. Which of the following motor is preferred for operation in highly explosive atmosphere ?
A. Series motor
B. Shunt motor
C. Air motor
D. Battery operated motor
733. 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
734. Which one of the following is not the function of pole shoes in a D.C. machine ?
A. To reduce eddy current loss
B. To support the field coils
C. To spread out flux for better uniformity
D. To reduce the reluctance of the magnetic path
735. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is______________?
A. 4.0
B. 2.0
C. 1.0
D. 0.5
736. 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. = | x supply voltage
C. supply voltage = | x back e.m.f
D. supply voltage = back e.m.f
737. For which of the following applications a D.C. motor is preferred over an A.C. motor ?
A. Low speed operation
B. High speed operation
C. Variable speed operation
D. Fixed speed operation
738. 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
739. Which D.C. motor is generally preferred for cranes and hoists ?
A. Series motor
B. Shunt motor
C. Cumulatively compounded motor
D. Differentially compounded motor
740. Three point starter can be used for______________?
A. series motor only
B. shunt motor only
C. compound motor only
D. both shunt and compound motor
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