DC MACHINES 4

 

DC MACHINES MCQ 4

 

1. The function of a commutator in a d.c. generator is
a) to collect current from conductors.
b) to change d.c. to a.c.
c) to conduct the current to the brushes.
d) to change a.c. to d.c.
ans. d

2. The current flowing in the conductors of a d.c. motor is
a) a.c.
b) d.c.
c) a.c as well as d.c.
d) transients.
ans. a

3. As the load is increased the speed of a d.c. shunt motor will
a) remain constant.
b) increase proportionately.
c) increase slightly.
d) reduce slightly.
ans. d

4. If the current in the armature of d.c. series motor is reduced to 5% , the torque of the motor will become
a) 50% of the previous value.
b) 25% of the previous value.
c) 150% of the previous value.
d) 125% of the previous value.
ans. b

5. In d.c. shunt motor, if the terminal voltage is reduced to half and torque remains the same. then,
a) speed will be half and armature current also will be half

b) speed will be half but armature current remains the same.
c) speed will be half and armature current becomes double.
d) speed and armature current will remain the same.
ans. c

6. The armature of d.c.motors is laminated
a) to reduce the hysteresis losses.
b) to reduce the eddy current losses.
c) to reduce the inductivity of armature.
d) to reduce the mass of the armature.
ans. b

7. Which of the following is a correct statement about a series motor?
a) Its field winding consists of thicker wire and less turns.
b) It can run easily without load.
c) It has almost constant speed.
d) It has poor torque.
ans. a

8. Which of the following d.c. motors has the least drop in the speed between no load to nominal load?
a) Shunt motor with commutating poles.
b) Series motor without commutating poles.
c) Compound motor without commutating poles.
d) Series motor with commutating poles.
ans. a

9. What happens if the field winding of a running shunt motor suddenly breaks open?
a) Its speed slows down
b) Its speed becomes dangerously high.
c) It gives out sparks.
d) It stops at once.
ans. b

10. The speed of a series motor at no load is
a) zero
b) 3000 rpm.
c) 3600 rpm.
d) infinity.
ans. d

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