Electrical Machines
In a DC generator sparking between brushes and commutator surface may be due to

  too rapid reversal of current.
 over commutation.
  under commutation.
  any of the above.

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Electrical Machines
In a 3 - Φ induction motor

  power factor at starting is low as compared to that while running.
  none of them.
  power factor at starting in the same as that while running.
  power factor at starting is high as compared to that while running.

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