MCQ on DC motor 41-60

41. In D.C. shunt motors as load is reduced
(a) the speed will increase abruptly
(b) the speed will increase in proportion to reduction in load
(c) the speed will remain almost/constant✔
(d) the speed will reduce

42. A D.C. series motor is that which
(a) has its field winding consisting of thick wire and less turns✔
(b) has a poor torque
(c) can be started easily without load
(d) has almost constant speed

43. For starting a D.C. motor a starter is required because
(a) it limits the speed of the motor
(b) it limits the starting current to a safe value✔
(c) it starts the motor
(d) none of the above

44. The type of D.C. motor used for shears and punches is
(a) shunt motor
(b) series motor
(c) differential compoutid D.C. motor
(d) cumulative compound D.C. motor✔

45. If a D.C. motor is connected across the A.C. supply it will
(a) run at normal speed
(b) not run
(c) run at lower speed
(d) burn due to heat produced in the field winding by .eddy currents✔

46. To get the speed of D.C, motor below the normal without wastage of electrical energy is used.
(a) Ward Leonard control✔
(b) rheostatic control
(c) any of the above method
(d) none of the above method

47. When two D.C. series motors are connected in parallel, the resultant speed is
(a) more than the normal speed
(b) loss than the normal speed
(c) normal speed✔
(d) zero

48. The speed of a D.C. shunt motor more than its full-load speed can be obtained by
(a) decreasing the field current✔
(b) increasing the field current
(c) decreasing the armature current
(d) increasing the armature current

49. In a D.C. shunt motor, speed is
(a) independent of armature current✔
(b) directly proportional to the armature current
(c) proportional to the square of the current
(d) inversely proportional to the armature current

50. A direct on line starter is used: for starting motors
(a) up to 5 H.P.✔
(b) up to 10 H.P.
(c) up to 15 H.P.
(d) up to 20 H.P.

51. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
(a) The motor will stop
(b) The motor will continue to run
(c) The armature may burn
(d) The motor will run noisy✔

52. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
(a) back e.m.f. is equal to armature drop
(b) armature drop is negligible
(c) flux is proportional to armature current
(d) flux is practically constant in D:C. shunt motors✔

53. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
(a) almost negligible
(b) rated full-load current
(c) less than full-load current
(d) more than full-load current✔

54. These days D.C. motors are widely used in
(a) pumping sets
(b) air compressors
(c) electric traction✔
(d) machine shops

55. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
(a) Frame
(b) Shaft
(c) Commutator✔
(d) Stator

56. In which of the following applications D.C. series motor is invariably tried?
(a) Starter for a car✔
(b) Drive for a water pump
(c) Fan motor
(d) Motor operation in A.C. or D.C.

57. In D.C. machines fractional pitch winding is used
(a) to improve cooling
(b) to reduce copper losses
(c) to increase the generated e.m.f.
(d) to reduce the sparking✔

58. A three point starter is considered suitable for
(a) shunt motors
(b) shunt as well as compound motors✔
(c) shunt, compound and series motors
(d) all D.C. motors

59. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
(a) 100%
(b) around 90%
(c) anywhere between 75% and 90%
(d) less than 50%✔

60. The ratio of starting torque to full-load torque is least in case of
(a) series motors
(b) shunt motors✔
(c) compound motors
(d) none of the above

MCQ on DC motor 21-40

21. The main disadvantage of the Ward-Leonard control method is
(a) high initial cost
(b) high maintenance cost
(c) low efficiency at Hght loads
(d) all of the above✔

22. Regenerative method of braking is based on that
(a) back e.m.f. is less than the applied voltage
(b) back e.m.f. is equal to the applied voltage✔
(c) back e.m.f. of rotor is more than the applied voltage
(d) none of above

23. The hysteresis loss in a D.C. machine least depends on
(a) Frequency of magnetic reversals
(b) Maximum value of flux density
(c) Volume and grade of iron
(d) Rate of flow of ventilating air✔

24. In a D.C. generator all of the following could be the effects of iron losses except
(a) Loss of efficiency
(b) Excessive heating of core
(c) Increase in terminal voltage✔
(d) Rise in temperature of ventilating air

25. 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 ?
(a) hysteresis loss
(b) field copper loss
(c) armature copper loss✔
(d) eddy current loss

26. Which of the following loss in a D.C. generator varies significantly with the load current ?
(a) Field copper loss
(b) Windage loss
(c) Armature copper loss✔
(d) None of the above

27. Torque developed by a D.C. motor depends upon
(a) magnetic field
(b) active length of the conductor
(c) current flow through the conductors
(d) all above factors✔

28. D.C. shunt motors are used for driving
(a) trains
(b) cranes
(c) hoists
(d) machine tools✔

29. In a manual shunt motor starter
(a) over load relay is connected in series and no volt relay in parallel with the load.✔
(6) over load relay is connected in parallel and no volt relay in series with the load
(c) over load relay and no volt relay are both connected in series with the load
(d) over load relay and no volt relay are both connected in parallel with the load

30. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
(a) Providing laminations in armature core
(b) Providing laminations in stator
(c) Using non-magnetic material for frame
(d) Using material of low hysteresis co-efficient for armature core material✔

31. During rheostat braking of D.C. series motors
(a) motor is run as a generator✔
(b) motor is reversed in direction
(c) motor is run at reduced speed
(d)all of above

32. For which types of D.C. motor, dynamic braking is generally used ?
(a) Shunt motors
(b) Series motors
(c) Compound motors
(d) All of the above✔

33. Which method of braking is generally used in elevators ?
(a) Plugging✔
(b) Regenerative braking
(c) Rheostatic braking
(d) None of the above

34. In variable speed motor
(a) a stronger commutating field is needed at low speed than at high speed
(b) a weaker commutating field is needed at low speed than at high speed✔
(c) same commutating field is needed at low speed than at high speed
(d) none of the above is correct

35. When the armature of a D.C. motor rotates, e.m.f. induced is
(a) self-induced e.m.f.
(b) mutually induced e.m.f.
(c) back e.m.f.✔
(d) none of the above

36. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
(a) drum type controller is used✔
(b) three point starter is used
(c) four point starter is used
(d) all above can be used

37. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
(a) this will make armature to take heavy current, possibly burning it✔
(b) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
(c) nothing will happen to motor
(d) motor will come to stop

38. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short
duration. We will select the
(a) series motor✔
(b) shunt motor
(c) compound motor
(d) any of the above

39. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this
(a) series motor
(b) shunt motor
(c) compound motor✔
(d) any of the above

40. Which D.C. motor has got maximum self relieving property ?
(a) Series motor✔
(6) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor

MCQ in DC motor 1-20

1. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
(a) regenerative
(b) plugging✔
(c) dynamic braking
(d) none of the above

2. Which of the following motors one will choose to drive the rotary compressor ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Universal motor
(d) Synchronous motor✔

3. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
(a) increase✔
(b) decrease
(c) remain same
(d) become zero

4. Why are the D.C. motors preferred for traction applications ?
(a) Torque and speed are inversely proportional to armature current
(b) Torque is proportional to armature current
(c) Torque is proportional to square root of armature current
(d) The speed is inversely proportional to the torque and the torque is proportional to square of armature current✔

5. Which of the following motors is usually used in house-hold refrigerators ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Single phase induction motor (split phase start or induction run motor)✔
(d) Reluctance motor

6. Which of the following motors is most suitable for signalling devices and many kinds of timers ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Induction motor
(d) Reluctance motor✔

7. Which motor should not be started on no-load ?
(a) Shunt motor
(b) Cumulatively compounded motor
(c) Differentially compounded motor.
(d)Series motor✔

8. Ward-Leonard control is basically a
(a) voltage control method✔
(b) field divertor method
(c) field control method
(d) armature resistance control method

9. For constant torque drive which speed control method is preferred ?
(a) Field control
(b) Armature voltage control✔
(c) Shunt armature control
(d) Mechanical loading system

10. In Ward-Leonard control the lower limit of speed is imposed by
(a) residual magnetism of the generator✔
(b) core losses of motor
(c) mechanical losses of motor and generator together
(d) all of the above

11. No-load speed of which of the following motor will be highest ?
(a) Shunt motor
(b) Series motor✔
(c) Cumulative compound motor
(d) Differentiate compound motor

12. The direction of rotation of a D.C. series motor can be changed by
(a) interchanging supply terminals
(b) interchanging field terminals✔
(c) either of (a) and (b) above
(d) None of the above

13. Which of the following application requires high starting torque ?
(a) Lathe machine
(b) Centrifugal pump
(c) Locomotive✔
(d) Air blower

14. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?
(a) Series motor✔
(b) Shunt motor
(c) Differentially compound motor
(d) Cumulative compound motor

15. Which D.C. motor will be preferred for machine tools ?
(a) Series motor
(b) Shunt motor✔
(c) Cumulative compound motor
(d) Differential compound motor

16. Differentially compound D.C. motors can find applications requiring
(a) high starting torque
(b) low starting torque✔
(c) variable speed
(d) frequent on-off cycles

17. Which D.C. motor is preferred for elevators ?
(a) Shunt motor
(b) Series motor
(c) Differential compound motor
(d) Cumulative compound motor✔

18. According to Fleming’s left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of
(a) current in the conductor aovtaat of conductor✔
(c) resultant force on conductor
(d) none of the above

19. If the field of a D.C. shunt motor gets opened while motor is running
(a) the speed of motor will be reduced %
(b) the armature current will reduce
(c) the motor will attain dangerously high speed 1✔
(d) the motor will continue to nuvat constant speed

20. Starters are used with D.C. motors because
(a) these motors have high starting torque
(b) these motors are not self-starting
(c) back e.m.f. of these motors is zero initially
(d) to restrict armature current as there is no back e.m.f. while starting✔