DC Motors MCQ Quiz - Multiple Choice Questions & Answers

1. The condition for maximum power in case of D.C. motor is

1. back e.m.f. = 2 x supply voltage
2. back e.m.f. = | x supply voltage
3. supply voltage = | x back e.m.f.
4. supply voltage = back e.m.f.

2. The current drawn by the armature of D.C. motor is directly proportional to

1. the torque required
2. the speed of the motor
3. the voltage across the terminals
4. none of the above

3. The direction of rotation of a D.C. series motor can be changed by

1. interchanging supply terminals
2. interchanging field terminals
3. either of a and b above
4. None of the above

4. The hysteresis loss in a D.C. machine least depends on

1. Frequency of magnetic reversals
2. Maximum value of flux density
3. Volume and grade of iron
4. Rate of flow of ventilating air

5. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?

1. hysteresis loss
2. field copper loss
3. armature copper loss
4. eddy current loss

6. The main disadvantage of the Ward-Leonard control method is

1. high initial cost
2. high maintenance cost
3. low efficiency at Hght loads
4. all of the above

7. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is

1. 4
2. 2
3. 1
4. 0.5

8. The plugging gives the

1. zero torque braking
2. smallest torque braking
3. highest torque braking
4. none of the above

9. The power mentioned on the name plate of an electric motor indicates

1. the power drawn in kW
2. the power drawn in kVA
3. the gross power
4. the output power available at the shaft

10. The purpose of retardation test on D.C. shunt machines is to find out

1. stray losses
2. eddy current losses
3. field copper losses
4. windage losses