Electrical Machines
The rotor speed of an induction motor is given by

  Nr = 120f / p × (1-s).
  Ns = 120f /p × ( 1 - r).
  Ns = 120f / p × ( 1 - s ).
None of these

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

 decrease in speed but armature current remains the same.
 increase in speed but armature currnet remains the same.
 decrease in speed demanding less armature current.
 increase in speed demanding more armature current.

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