July 2018

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

The condition for maximum power in case of D.C. motor is______________?

A. back e.m.f. = 2 x supply voltage
B. back e.m.f. = | x supply voltage
C. supply voltage = | x back e.m.f
D. supply voltage = back e.m.f

A. 4.0
B. 2.0
C. 1.0
D. 0.5

Which one of the following is not the function of pole shoes in a D.C. machine ?

A. To reduce eddy current loss
B. To support the field coils
C. To spread out flux for better uniformity
D. To reduce the reluctance of the magnetic path

If the supply voltage for a D.C. motor is increased, which of the following will decrease ?

A. Starting torque
B. Operating speed
C. Full-load current
D. All of the above

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

Sparking at the commutator of a D.C. motor may result in____________?

A. damage to commutator segments
B. damage to commutator insulation
C. increased power consumption
D. all of the above

In case of conductively compensated D.C. series motors, the compensating winding is provided______________?

A. as separately wound unit
B. in parallel with armature winding
C. in series with armature winding
D. in parallel with field winding

For the same H.P. rating and full load speed, following motor has poor starting torque_____________?

A. shunt
B. series
C. differentially compounded
D. cumulativelyc’ompounded

D.C. series motors are used______________?

A. where load is constant
B. where load changes frequently
C. where constant operating speed is needed
D. in none of the above situations