DC MACHINES 2

 

DC MACHINES MCQ 2

 

1. What is the effect produced by the electric current in an electric motor?
a) magnetic effect only.
b) magnetic as well as heating effect.
c) heating effect only.
d) heating as well as chemical effect.
ans. b

2. The rotating part of a d.c. motors is known as
a) pole
b) stator
c) armature
d) carbon brush.
ans. c

3. Why is the airgap between the yoke and armature of an electric motor kept smaller?
a) To achieve a stronger magnetic field.
b) To avoid overheating of the machine.
c) To make station easier.
d) None of these.
ans. a

4. The function of the commutator in a d.c. machine is
a) to change alternating current to direct current.
b) to improve commutation.
c) for easy speed control.
d) to change alternating voltage to direct voltage.
ans. d

5. Carbon brushes are used in electric motors to
a) brush off carbon deposits on the commutator.
b) provide a path for flow of current.
c) prevent overheating of armature windings.
d) prevent sparking during commutation.
ans. b

6. An external resistance is added in the field of a d.c. shunt generator will
a) increase the speed of the generator.
b) increase the voltage of the generator.
c) decrease the voltage of the generator.
d) increase the power delivered.
ans. c

7. The speed of a d.c. shunt motor is required to be more than F.L. speed. This is possible by
a) increasing the armature current.
b) decreasing the armature current.
c) increasing the excitation current.
d) reducing the field current.
ans. d

8. An emf is induced in the windings of an armature of a d.c. generator when the armature rotates inā
a) alternating magnetic flux.
b) magnetic field.
c) electrostatic field.
d) electromagnetic flux.
ans. b

9. If the speed of d.c. the generator is increased, the generated emf
a) increases
b) decreases
c) remains constant
d) decreases and then increases.
ans. a

10. If the speed of a d.c. shunt motor increases, the back emf
a) increases
b) decreases
c) remains constant
d) first decreases and then increases.
ans. a

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