DC Motors

No-load speed of which of the following motor will be highest ?

• Shunt Motor

• Series Motor

• Cumulative Compound Motor

• Differential Compound Motor

The direction of rotation of a D.C. series motor can be changed by

• (a) interchanging supply terminals

• (b) interchanging field terminals

• either a and b

• none of the above

Which of the following application requires high starting torque ?

• Lathe machine

• Centrifugal Pump

• Locomotive

• Air blower

If a D.C. motor is to be selected for conveyors, which motor would be preferred ?

• Series Motor

• Shunt Motor

• Differential Compound Motor

• Cumulative Compound Motor

Which D.C. motor will be preferred for machine tools ?

• Series motor

• Shunt motor

• Cumulative Compound motor

• Differential Compound motor

Differentially compound D.C. motors can find applications requiring

• high starting torque

• low starting torque

• variable speed

• frequent on-off cycles

Which D.C. motor is preferred for elevators ?

• Shunt motor

• Series motor

• Differential compound motor

• Cumulative compound motor

According to Fleming’s left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of

• current in the conductor

• Lines of flux

• resultant force on conductor

• none of the above

Starters are used with D.C. motors because

• the motors have high starting torque

• these motors are not self-starting

• back e.m.f. of these motors is zero initially

• to restrict armature current as there is no back e.m.f. while starting

If the field of a D.C. shunt motor gets opened while motor is running

• the speed of motor will be reduced %

• the armature current will reduce

• the motor will attain dangerously high speed

• the motor will remain constant