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Multiple Choice Question (MCQ) of D.C. Machines page-1

1.A shunt motor is fitted with a field regulator for speed control. For constant torque load, the speed will be minimum when the resistance of the regulator is

a) 0Ω
b) Infinite
c) About 10Ω
d) About 100Ω

Ans: (a)

2. Carbon brushes are used in electric motors to

a) Prevent sparking during commutation
b) Provide a path for flow of current
c) Brush off carbon deposits on the commutator
d) None 0f these

Ans: (b)

3. The resistance of the field regulator of a dc shunt motor is of order of

a) 0.1Ω
b) 1Ω
c) 10Ω
d) 100Ω

Ans: (d)

4. Interpoles in dc motors are used for

a) Increasing the speed of motor
b) Reducing sparking at the commutation
c) Decreasing the counter emf
d) Converting armature current to dc

Ans: (b)

5. The dc compound motors are generally

a) Cumulative compound
b) Differential compound
c) Level compound
d) None of these

Ans: (a)

6. Small dc motors upto 5 HP usually have

a) 2 poles
b) 4 poles
c) 6 poles
d) 8 poles

Ans: (a)

7. The air gap between stator and armature of an electric motor is kept as small as possible

a) To get a stronger magnetic field
b) To improve the air circulation
c) To reach a higher speed of rotation
d) To make the rotation easier

Ans: (a)

8. The resistance of the starter of a 220 v, 5 HP dc shunt motor is of the order of

a) 0.01Ω
b) 0.1Ω
c) 1Ω
d) 10Ω

Ans: (d)

9. In a dc motor, unidirectional torque is produced with the help of

a) Brushes
b) Commutator
c) End plates
d) Both (a) and (b)

Ans: (d)

10. A dc motor can be easily identified by

a) Yoke
b) Size of conductor
c) Commutator
d) Winding

Ans: (c)

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