D.C. Motors

If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will_________?

A. increase
B. decrease
C. remain same
D. become zero

Which of the following motors one will choose to drive the rotary compressor ?

A. D.C. shunt motor
B. D.C. series motor
C. Universal motor
D. Synchronous motor

If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking?

A. regenerative
B. plugging
C. dynamic braking
D. none of the above
E. any of the above

If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor_____________?

A. of lower H.P. should be selected
B. of higher H.P. should be selected
C. can be used for 50°C ambient temperature also
D. is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor

The armature voltage control of D.C. motor provides_____________?

A. constant voltage drive
B. constant current drive
C. constant torque drive
D. none of the above

The plugging gives the____________?

A. zero torque braking
B. smallest torque braking
C. highest torque braking
D. none of the above

For a D.C. shunt motor if the excitation is changed_______________?

A. torque will remain constant
B. torque will change but power will remain constant
C. torque and power both will change
D. torque, power and speed, all will change

Which motor has the poorest speed control?

A. Differentially compounded motor
B. Cumulatively compounded motor
C. Shunt motor
D. Series motor

If I2 be the armature current, then speed of a D.C. shunt motor is_______________?

A. independent of Ia
B. proportional to la
C. varies as (Ia)
D. varies as la

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