1. In a dc machine without interpoles to get improved commutation , the brush shift angle must be
a) varied with change in load
b) kept constant
c) 0 degree
d) none of these
ans. a
2. Compared to the air-gap under the field-poles, the inter-pole air-gap is made
a) larger for both the generators and the motors.
b) smaller for both the generators and larger for the motor.
c) smaller for generator and larger for the motors.
d) larger for generators and smaller for the motors.
ans. a
3. Compared to an uncompensated dc machine , the interpole as required in a compensated dc machine is
a) larger for the generators and smaller for the motors.
b) smaller for the generators and larger for the motors
c) smaller for both the generators and the motors.
d) larger for both the generators and the motors.
ans. c
4. Due to magnetic saturation , the flux per pole in a dc machine without brush shift
a) decrease the generators and increases in the motors with load.
b) decreases in both the generators and the motors with load.
c) increases in both the generators and the motors with load.
d) increases in the generators and decreases in the motors with load.
ans. b
5. The core losses in a dc machine occur due to
a) hysteresis only
b) eddy current only
c) armature current
d) both hysteresis and eddy currents.
ans. b
6. The core losses in a dc machine occur in
a) the armature only
b) the pole faces only
c) the yoke only
d) both the armature and the pole faces.
ans. d
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
a) varied with change in load
b) kept constant
c) 0 degree
d) none of these
ans. a
2. Compared to the air-gap under the field-poles, the inter-pole air-gap is made
a) larger for both the generators and the motors.
b) smaller for both the generators and larger for the motor.
c) smaller for generator and larger for the motors.
d) larger for generators and smaller for the motors.
ans. a
3. Compared to an uncompensated dc machine , the interpole as required in a compensated dc machine is
a) larger for the generators and smaller for the motors.
b) smaller for the generators and larger for the motors
c) smaller for both the generators and the motors.
d) larger for both the generators and the motors.
ans. c
4. Due to magnetic saturation , the flux per pole in a dc machine without brush shift
a) decrease the generators and increases in the motors with load.
b) decreases in both the generators and the motors with load.
c) increases in both the generators and the motors with load.
d) increases in the generators and decreases in the motors with load.
ans. b
5. The core losses in a dc machine occur due to
a) hysteresis only
b) eddy current only
c) armature current
d) both hysteresis and eddy currents.
ans. b
6. The core losses in a dc machine occur in
a) the armature only
b) the pole faces only
c) the yoke only
d) both the armature and the pole faces.
ans. d
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
