D.C. Motors

1. 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

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2. 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

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

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

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4. 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

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5. 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

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

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6. As -the load is increased the speed of D.C. shunt motor will

1. reduce slightly
2. increase slightly
3. increase proportionately
4. remains unchanged

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7. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit

1. a resistance is connected in series with armature
2. a resistance is connected parallel to the armature
3. armature is temporarily open circuited
4. a high value resistor is connected across the field winding

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8. At the instant of starting when a D.C. motor is put on supply, it behaves like

1. a highly resistive circuit
2. a low resistance circuit
3. a capacitive circuit
4. none of the above

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9. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of

1. D.C. series motor
2. D.C. shunt motor
3. induction motor
4. all of above motors

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10. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?

1. Frame
2. Shaft
3. Commutator
4. Stator

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