DC Motors Questions and Answers | Online Quiz for Practice

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

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

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

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

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

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

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

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

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

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

51. Which of the following motors one will choose to drive the rotary compressor ?

1. D.C. shunt motor
2. D.C. series motor
3. Universal motor
4. Synchronous motor

52. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?

1. Providing laminations in armature core
2. Providing laminations in stator
3. Using non-magnetic material for frame
4. Using material of low hysteresis co-efficient for armature core material

53. Which of the following tests will be suitable for testing two similar D.C. series motorsof large capacity ?

1. Swinburnes test
2. Hopkinsons test
3. Field test
4. Brake test

54. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?

1. Low cost
2. Wide speed range
3. Stability
4. High starting torque.

55. Which one of the following is not the function of pole shoes in a D.C. machine ?

1. To reduce eddy current loss
2. To support the field coils
3. To spread out flux for better unifor-mity
4. To reduce the reluctance of the mag-netic path

56. Why are the D.C. motors preferred for traction applications ?

1. Torque and speed are inversely proportional to armature current
2. Torque is proportional to armature current
3. Torque is proportional to square root of armature current
4. The speed is inversely proportional to the torque and the torque is proportional to square of armature current

57. A D.C. series motor is that which

1. has its field winding consisting of thick wire and less turns
2. has a poor torque
3. can be started easily without load
4. has almost constant speed

58. A direct on line starter is used: for starting motors

1. iip to 5 H.P.
2. up to 10 H.P.
3. up to 15 H.P.
4. up to 20 H.P.

59. A three point starter is considered suitable for

1. shunt motors
2. shunt as well as compound motors
3. shunt, compound and series motors
4. all D.C. motors

60. According to Flemings left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of

1. current in the conductor aovtaat of conductor
2. resultant force on conductor
3. none of the above