Electrical Machines
What is the frequency of a alternator, if P = number of poles and N = revolution made per second?

  PN / 2 Hz.
 120 / PN Hz.
 120N / P Hz.
 120P / N Hz.

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Electrical Machines
For a given torque, reducing divertor resistance of a DC series motor

  Increase in speed but armature currnet remains the same.
  Decrease in speed demanding less armature current.
  Decrease in speed but armature current remains the same.
  Increase in speed demanding more armature current.

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Electrical Machines
In a DC generator, the armature reaction results in

  demagnetization of leading & magnetization of trailing pole tip.
  magnetization of inter poles.
 demagnetization of centers of poles.
 magnetization of leading and demagnetization of trailing pole tip.

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