DC MACHINES 8

 

DC MACHINES MCQ 8

1. The main function of a commutator in dc motor is to
a) prevent sparking
b) convert ac to dc
c) reduce friction
d) convert dc to ac
ans. b

2. Which of the following statements is incorrect? If a starter is not used with large dc motor. It will draw a starting current which
a) is many times its full-load current
b) will produce excessive line voltage
c) will damage the commutator
d) will produce very low starting torque
ans. d

3. The factor which voltage does not cause decrease in the terminal voltage of a shunt generator is
a) armature resistance
b) armature reaction
c) reduction in field current
d) armature reactance
ans. d

4. A dc generator can be termed as
a) rotating amplifier.
b) prime mover.
c) power pump.
d) none of these
ans. a

5. The rated speed of a given dc shunt motor is 1050 rpm.To run this machine at 1200rpm , which of the following speed control scheme will be used
a) Armature current resistance control
b) Field resistance control
c) Ward-Leonard control
d) none of these
ans. b

6. The destroyed residual magnetism of a shunt generator may restored by connecting its shunt field to
a) earth
b) generator
c) a battery
d) none of these
ans. d

7. It is preferable to start a dc series motor with some mechanical load on it because
a) it will not run at no load
b) it acts as a starter to the motor
c) it may develop excessive speed and damage itself
d) none of these
ans. c

8. If the flux of a dc motor approaches zero, its speed will approach
a) infinity
b) zero
c) a stable value nearer to the rated speed
d) none of these
ans. a

9. As the load is increased, speed of a shunt motor
a) remains constant
b) increases slightly
c) reduces slightly
d) none of these
ans. c

10. A 230 V dc series motor is connected to 230 V ac it will
a) run slowly
b) not run at all
c) run with less efficiency
d) none of these
ans. c

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