11. In a d.c. motor the iron losses occur in
a) the yoke
b) the armature
c) the field.
d) None of these.
ans. a
12. The dummy coil in d.c. machines used to
a) eliminate reactance voltage.
b) eliminate armature reaction.
c) bring about mechanical balance of armature.
d) eliminate harmonics developed in the machine.
ans. c
13. A simple method of increasing the voltage of an d.c. generator is
a) to decrease the air gap flux density
b) to increase the speed of rotation.
c) to decrease the speed of rotation.
d) to increase the length of the armature.
ans. b
14. The function of starter in a d.c. machine is
a) to avoid the excessive current at starting
b) to control the speed.
c) to avoid armature reaction.
d) to increase the length of the armature.
ans. b
15. An external resistance is added in the series with the field of a d.c. shunt motor. When the motor runs, the effect of resistance is
a) to reduce the speed of the motor
b) to increase the speed of the motor.
c) to reduce the armature current drawn by the motor
d) to reduce the losses.
ans. b
16. 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
17. 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
18. An emf is induced in the windings of an armature of a d.c. generator when the armature rotates in
a) alternating magnetic flux.
b) magnetic field.
c) electrostatic field.
d) electromagnetic flux.
ans. b
19. If the speed of d.c. generator is increased, the generated emf
a) increases
b) decreases
c) remains constant
d) decreases and then increases.
ans. a
20. 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
a) the yoke
b) the armature
c) the field.
d) None of these.
ans. a
12. The dummy coil in d.c. machines used to
a) eliminate reactance voltage.
b) eliminate armature reaction.
c) bring about mechanical balance of armature.
d) eliminate harmonics developed in the machine.
ans. c
13. A simple method of increasing the voltage of an d.c. generator is
a) to decrease the air gap flux density
b) to increase the speed of rotation.
c) to decrease the speed of rotation.
d) to increase the length of the armature.
ans. b
14. The function of starter in a d.c. machine is
a) to avoid the excessive current at starting
b) to control the speed.
c) to avoid armature reaction.
d) to increase the length of the armature.
ans. b
15. An external resistance is added in the series with the field of a d.c. shunt motor. When the motor runs, the effect of resistance is
a) to reduce the speed of the motor
b) to increase the speed of the motor.
c) to reduce the armature current drawn by the motor
d) to reduce the losses.
ans. b
16. 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
17. 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
18. An emf is induced in the windings of an armature of a d.c. generator when the armature rotates in
a) alternating magnetic flux.
b) magnetic field.
c) electrostatic field.
d) electromagnetic flux.
ans. b
19. If the speed of d.c. generator is increased, the generated emf
a) increases
b) decreases
c) remains constant
d) decreases and then increases.
ans. a
20. 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
