DC Motors Multiple Choice Questions and Answers

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