1. If the armature current of a dc motor is increased keeping the field flux constant, then the developed torque
a) increases proportionally.
b) decreases in inverse proportion.
c) remains constant.
d) increases proportionally to the square of the current.
ans. a
2. The direction of induced emf in an armature coil of a dc machine is
a) the same as that of the current for both the generator and the motor.
b) opposite to that of the current for the generator and the motor.
c) the same as that of current for the generator and opposite to that of the current for the motor.
d) none of these.
ans. c
3.In a dc machine the armature mmf is always directed along the
a) polar axis
b) brush axis
c) interpolar axis
d) none of these
ans. b
4. In a dc machine without any brush shift, the shift of the magnetic neutral axes due to armature is
a) in the direction of rotation for the generator and against the direction of rotation for the motor.
b) in the direction of rotation for both the generator and the motor.
c) against the direction of rotation for both the generator and the motor
d) against the direction of rotation for the generator and in the direction of rotation
ans. a
5. The wave form of the armature mmf in a dc machine is
a) square
b) rectangular
c) triangular
d) sinusoidal
ans. c
6. The commutator of a dc machine acts as a
a) full wave rectifier
b) half wave rectifier
c) controlled full-wave rectifier.
d) controlled half-wave rectifier.
ans. a
7. In a dc machine the armature reaction and the inductance of the commutating coils result in
a) over-commutation
b) sinusoidal commutation
c) linear commutation
d) under commutation
ans. d
8. Under commutation gives rise to
a) sparking at the leading edge of the brush
b) sparking at the trailing edge of the brush
c) no sparking at all
d) sparking at the middle of the brush
ans. b
9. For a dc generator if the brushes are given , a small amount forward shift the effect of armature reaction is
a) totally demagnetizing
b) totally magnetizing
c) partly demagnetizing and partly cross magnetizing
d) totally cross-magnetizing
ans. c
10. In a dc motor if the brushes are given backward shift , then
a) commutation is worsened and speed decreases
b) commutation is improved and speed decreases
c) commutation is unaffected and speed increases
d) commutation is improved and speed increases
ans. d
a) increases proportionally.
b) decreases in inverse proportion.
c) remains constant.
d) increases proportionally to the square of the current.
ans. a
2. The direction of induced emf in an armature coil of a dc machine is
a) the same as that of the current for both the generator and the motor.
b) opposite to that of the current for the generator and the motor.
c) the same as that of current for the generator and opposite to that of the current for the motor.
d) none of these.
ans. c
3.In a dc machine the armature mmf is always directed along the
a) polar axis
b) brush axis
c) interpolar axis
d) none of these
ans. b
4. In a dc machine without any brush shift, the shift of the magnetic neutral axes due to armature is
a) in the direction of rotation for the generator and against the direction of rotation for the motor.
b) in the direction of rotation for both the generator and the motor.
c) against the direction of rotation for both the generator and the motor
d) against the direction of rotation for the generator and in the direction of rotation
ans. a
5. The wave form of the armature mmf in a dc machine is
a) square
b) rectangular
c) triangular
d) sinusoidal
ans. c
6. The commutator of a dc machine acts as a
a) full wave rectifier
b) half wave rectifier
c) controlled full-wave rectifier.
d) controlled half-wave rectifier.
ans. a
7. In a dc machine the armature reaction and the inductance of the commutating coils result in
a) over-commutation
b) sinusoidal commutation
c) linear commutation
d) under commutation
ans. d
8. Under commutation gives rise to
a) sparking at the leading edge of the brush
b) sparking at the trailing edge of the brush
c) no sparking at all
d) sparking at the middle of the brush
ans. b
9. For a dc generator if the brushes are given , a small amount forward shift the effect of armature reaction is
a) totally demagnetizing
b) totally magnetizing
c) partly demagnetizing and partly cross magnetizing
d) totally cross-magnetizing
ans. c
10. In a dc motor if the brushes are given backward shift , then
a) commutation is worsened and speed decreases
b) commutation is improved and speed decreases
c) commutation is unaffected and speed increases
d) commutation is improved and speed increases
ans. d
