Electrical Machines
When R2 is rotor resistance, X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running condition will be

  sR2 = X2.
  R2 = s2X2.
  R2 = sX2.
  R2 = s2X2.

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Electrical Machines
No load primary current in a transformer

 lags behind applied voltage by exactly 90Â&am
 leads the applied voltage somewhat less than 90Ã&
 lags behind applied voltage somewhat less than 90Ã
 leads the applied voltage by exactly 90Â&

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