A. field control method
B. armature controlled method
C. field diverter
D. frequency control method
D.C. Motors
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
Which method of braking is generally used in elevators ?
A. Plugging
B. Regenerative braking
C. Rheostatic braking
D. None of the above
Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
A. Lenz’s law
B. Faraday’s law
C. Coloumb’s law
D. Fleming’s left-hand rule
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
Why are the D.C. motors preferred for traction applications ?
A. Torque and speed are inversely proportional to armature current
B. Torque is proportional to armature current
C. Torque is proportional to square root of armature current
D. The speed is inversely proportional to the torque and the torque is proportional to square of armature current
One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven_______________?
A. runs as a generator
B. does not run as a generator
C. also runs as a motor comes to stop after sometime
The armature torque of the D.C. shunt motor is proportional to____________?
A. field flux only
B. armature current only
C. both A. and B.
D. none of the above
In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to
A. 100% of the previous value
B. 50% of the previous value
C. 25% of the previous value
D. 10% of the previous value
E. none of the above
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
