In D.C. motor which of the following can sustain the maximum temperature rise?

In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be______________?

A. 100%
B. around 90%
C. anywhere between 75% and 90%
D. less than 50%

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

In a differentially compounded D.C. motor, if shunt field suddenly opens____________?

A. the motor will first stop and then run in opposite direction as series motor
B. the motor will work as series motor and run at slow speed in the same direction
C. the motor will work as series motor and run at high speed in the same direction
D. the motor will not work and come to stop

D.C. shunt motors are used for driving____________?

A. trains
B. cranes
C. hoists
D. machine tools

Ward-Leonard control is basically a____________?

A. voltage control method
B. field divertor method
C. field control method
D. armature resistance control method

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