DC Motors MCQs Quiz Multiple Choice Questions & Answers

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

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

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

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

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

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

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

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

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

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

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

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. 2
2. 1
3. 0.5
4. 4

8. The plugging gives the

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

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

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

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

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

11. The ratio of starting torque to full-load torque is least in case of

1. shunt motors
2. compound motors
3. none of the above
4. series motors

12. The speed of a D.C. motor can be varied by varying

1. applied voltage
2. resistance in series with armature
3. any of the above
4. field current

13. The speed of a D.C. series motor is

1. proportional to the square of the armature current
2. proportional to field current
3. inversely proportional to the armature current
4. proportional to the armature current

14. The speed of a D.C. shunt motor can be increased by

1. increasing the resistance in field circuit
2. reducing the resistance in the field circuit
3. reducing the resistance in the armature circuit
4. increasing the resistance in armature circuit

15. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by

1. decreasing the armature current
2. increasing the armature current
3. increasing the excitation current
4. reducing the field current

16. The speed of a D.C. shunt motor more than its full-load speed can be obtained by

1. increasing the field current
2. decreasing the armature current
3. increasing the armature current
4. decreasing the field current

17. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is

1. 4.76%
2. 6.77%
3. 8.84%
4. 2.36%

18. The starting resistance of a D.C. motor is generally

1. around 500 Q
2. 1000 Q
3. infinitely large
4. low

19. The total losses in a well designed D.C. generator of 10 kW will be nearly

1. 500 W
2. 1000 W
3. 1500 W
4. 100 W

20. The type of D.C. motor used for shears and punches is

1. series motor
2. differential compoutid D.C. motor
3. cumulative compound D.C. motor
4. shunt motor

21. These days D.C. motors are widely used in

1. air compressors
2. electric traction
3. machine shops
4. pumping sets

22. Three point starter can be used for

1. shunt motor only
2. compound motor only
3. both shunt and compound motor
4. series motor only

23. To get the speed of D.C, motor below the normal without wastage of electrical energy is used.

1. rheostatic control
2. any of the above method
3. none of the above method
4. Ward Leonard control

24. Torque developed by a D.C. motor depends upon

1. active length of the conductor
2. current flow through the conductors
3. all above factors
4. magnetic field

25. Usually wide and sensitive speed control is desired in case of

1. elevators
2. steel rolling mills
3. colliery winders
4. centrifugal pumps

26. Ward-Leonard control is basically a

1. field divertor method
2. field control method
3. armature resistance control method
4. voltage control method

27. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?

1. The motor will continue to run
2. The armature may burn
3. The motor will run noisy
4. The motor will stop

28. When the armature of a D.C. motor rotates, e.m.f. induced is

1. mutually induced e.m.f.
2. back e.m.f.
3. none of the above
4. self-induced e.m.f.

29. When two D.C. series motors are connected in parallel, the resultant speed is

1. loss than the normal speed
2. normal speed
3. zero
4. more than the normal speed

30. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversingand speed control

1. three point starter is used
2. four point starter is used
3. all above can be used
4. drum type controller is used

31. Which D.C. motor has got maximum self loading property?

1. Shunt motor
2. Cumulatively compounded motor
3. Differentially compounded motor
4. Series motor

32. Which D.C. motor has got maximum self relieving property ?

1. Shunt motor
2. Cumulatively compounded motor
3. Differentially compounded motor
4. Series motor

33. Which D.C. motor is generally preferred for cranes and hoists ?

1. Shunt motor
2. Cumulatively compounded motor
3. Differentially compounded motor
4. Series motor

34. Which D.C. motor is preferred for elevators ?

1. Series motor
2. Differential compound motor
3. Cumulative compound motor
4. Shunt motor

35. Which D.C. motor will be preferred for machine tools ?

1. Shunt motor
2. Cumulative compound motor
3. Differential compound motor
4. Series motor

36. Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?

1. Shunt motor
2. Cumulatively compounded motor
3. Differentially compounded motor
4. Series motor

37. Which method of braking is generally used in elevators ?

1. Regenerative braking
2. Rheostatic braking
3. None of the above
4. Plugging

38. Which motor has the poorest speed control?

1. Cumulatively compounded motor
2. Shunt motor
3. Series motor
4. Differentially compounded motor

39. Which motor should not be started on no-load ?

1. Shunt motor
2. Cumulatively compounded motor
3. Differentially compounded motor.
4. Series motor

40. Which of the following application requires high starting torque ?

1. Centrifugal pump
2. Locomotive
3. Air blower
4. Lathe machine

41. Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?

1. Faradays law
2. Coloumbs law
3. Flemings left-hand rule
4. Lenzs law

42. Which of the following load normally needs starting torque more than the rated torque?

1. Conveyors
2. Air compressors
3. Centrifugal pumps
4. Blowers

43. Which of the following loss in a D.C. generator is dissipated in the form of heat?

1. Core loss
2. Copper loss
3. All of the above
4. Mechanical loss

44. Which of the following loss in a D.C. generator varies significantly with the load current ?

1. Windage loss
2. Armature copper loss
3. None of the above
4. Field copper loss

45. Which of the following losses are significantly reduced by laminating the core of aD.C. generator ?

1. Eddy current losses
2. Copper losses
3. Windage losses
4. Hysteresis losses

46. Which of the following method of speed control of D.C. machine will offer minimum efficiency ?

1. Field control method
2. Armature control method
3. All above methods
4. Voltage control method

47. Which of the following motor has the poorest speed regulation ?

1. Series motor
2. Differential compound motor
3. Cumulative compound motor
4. Shunt motor

48. Which of the following motor is preferred for operation in highly explosive atmosphere ?

1. Shunt motor
2. Air motor
3. Battery operated motor
4. Series motor

49. Which of the following motors is most suitable for signalling devices and many kinds of timers ?

1. D.C. series motor
2. Induction motor
3. Reluctance motor
4. D.C. shunt motor

50. Which of the following motors is usually used in house-hold refrigerators ?

1. D.C. series motor
2. Single phase induction motor (split phase start or induction run motor)
3. Reluctance motor
4. D.C. shunt motor