In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
A. Remain unchanged
B. Reduce to one-fourth value
C. Increase four folds
D. Be doubled
Answer: Option A
This Question Belongs to Electrical Engineering >> D.C. Motors
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The condition for maximum efficiency for a D.C. generator is
A. Eddy current losses = stray losses
B. Hysteresis losses = eddy current losses
C. Copper losses = 0
D. Variable losses = constant losses
If a D.C. motor is connected across the A.C. supply it will
A. Run at normal speed
B. Not run
C. Run at lower speed
D. Burn due to heat produced in the field winding by eddy currents
The speed of a D.C. shunt motor can be increased by
A. Increasing the resistance in armature circuit
B. Increasing the resistance in field circuit
C. Reducing the resistance in the field circuit
D. Reducing the resistance in the armature circuit
The armature voltage control of D.C. motor provides
A. Constant torque drive
B. Constant voltage drive
C. Constant current drive
D. None of the above
Explanation: Torque depends on armature current, so as long as armature current remains constant torque will not change. Speed depends directly with back emf thus, it will definitely become double when back emf is doubled.