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Polyphase Induction Motors - section-1
  1. The low power factor of induction motor is due to

    2. A.

     Rotor leakage reactance
    B.

     Stator reactance
    C.

     The reactive lagging magnetizing current necessary to generate the magnetic flux
    D.

     All of the above

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  2. The injected e.m.f. in the rotor of induction motor must have

    3. A.

     Zero frequency
    B.

     The same frequency as the slip frequency
    C.

     The same phase as the rotor e.m.f.
    D.

     High value for the satisfactory speed control

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  3. If any two phases for an induction motor are interchanged

    4. A.

     The motor will run in reverse direction
    B.

     The motor will run at reduced speed
    C.

     The motor will not run
    D.

     The motor will burn

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  4. Slip of an induction motor is negative when

    5. A.

     Magnetic field and rotor rotate in opposite direction
    B.

     Rotor speed is less than the synchronous speed of the field and are in the same direction
    C.

     Rotor speed is more than the synchronous speed of the field and are in the same direction
    D.

     None of the above

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  5. The torque developed by a 3-phase induction motor least depends on

    6. A.

     Rotor current
    B.

     Rotor power factor
    C.

     Rotor e.m.f.
    D.

     Shaft diameter

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  6. The good power factor of an induction motor can be achieved if the average flux density in the air gap is

    7. A.

     Absent
    B.

     Small
    C.

     Large
    D.

     Infinity

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  7. The rotor of an induction motor runs at

    8. A.

     Synchronous speed
    B.

     Below synchronous speed
    C.

     Above synchronous speed
    D.

     Any of the above

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  8. In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be

    9. A.

     Ns
    B.

     s.N
    C.

     (l-s) Ns
    D.

     (Ns-l) s

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  9. Which of the following component is usually fabricated out of silicon steel?

    10. A.

     Bearings
    B.

     Shaft
    C.

     Stator core
    D.

     None of the above

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  10. Insertion of resistance in the rotor of an induction motor to develop a given torque

    11. A.

     Decreases the rotor current
    B.

     Increases the rotor current
    C.

     Rotor current becomes zero
    D.

     Rotor current remains same

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