D.C. Machines

21. As the voltage of transmission increases, the volume of conductor

1. increases.
2. does not change.
3. decreases.
4. increases proportionately.

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22. Both Hopkinson's test and Field test

1. Require two electrically coupled series motors
2. Need two similar mechanically coupled motors
3. Use negligible power
4. Are regenerative tests

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23. If a transformer primary is energised from a square wave voltage source, its output voltage will be

1. A square wave.
2. A sine wave.
3. A triangular wave.
4. A pulse wave.

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24. The speed of an induction motor

1. decreases too much with the increase of load
2. increase with the increase of load
3. decreases slightly with the increase of load
4. remains constant with the increase of load

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25. If the field of a synchronous motor is under excited, the power factor will be

1. Lagging
2. Leading
3. Unity
4. More than unity

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26. In a 3 – phase induction motor the maximum torque

1. is proportional to rotor resistance r2 .
2. does not depend on r2 .
3. is proportional to square root of r2 .
4. is proportional to square of r2 .

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27. The current from the stator of an alternator is taken out to the external load circuit through

1. slip rings.
2. commutator segments.
3. solid connections.
4. carbon brushes.

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28. In a capacitor start single-phase induction motor, the capacitor is connected

1. in series with main winding.
2. in series with auxiliary winding.
3. in series with both the windings.
4. in parallel with auxiliary winding.

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29. In a D.C. machine, the armature mmf is

1. stationary w.r.t. armature.
2. rotating w.r.t. field.
3. stationary w.r.t. field.
4. rotating w.r.t. brushes.

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30. In a dc generator, the generator, the generated emf is directly proportional to the

1. field current
2. pole flux
3. number of armature parallel paths
4. number of dummy coils

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