D.C. Motors

The power mentioned on the name plate of an electric motor indicates____________?

A. the power drawn in kW
B. the power drawn in kVA
C. the gross power
D. the output power available at the shaft

The current drawn by the armature of D.C. motor is directly proportional to__________?

A. the torque required
B. the speed of the motor
C. the voltage across the terminals
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. series motor is_____________?

A. proportional to the armature current
B. proportional to the square of the armature current
C. proportional to field current
D. inversely proportional to the armature current

The starting resistance of a D.C. motor is generally_______________?

A. low
B. around 500 Q
C. 1000 Q
D. infinitely large

Which of the following load normally needs starting torque more than the rated torque?

A. Blowers
B. Conveyors
C. Air compressors
D. Centrifugal pumps

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

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

A. Slip rings
B. Commutator
C. Field winding
D. Armature winding

The ratio of starting torque to full-load torque is least in case of____________?

A. series motors
B. shunt motors
C. compound motors
D. none of the above

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%