DC MACHINES 10

 

DC MACHINES MCQ 10

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 proportional to 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. The hysteresis loss per unit weight is
a) proportional to the frequency
b) inversely proportional to the frequency
c) inversely proportional to the flux density
d) proportional to the thickness of lamination's.
ans. a

8. If the thickness of lamination's is increased , then
a) the eddy current loss decreases
b) the eddy current loss increases
c) the hysteresis loss decreases
d) the hysteresis loss increases
ans. b

9. Ohmic losses in a dc machine occur in
a) the armature winding only
b) the field winding only
c) the brush contact only
d) the armature winding , the field winding and also in the brush contact.
ans. d

10. The efficiency of a dc machine is maximum when the variable losses equal to
a) the constant losses
b) the square of the constant losses.
c) the square root of the constant losses
d) zero.
ans. a

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