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

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

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Electrical Machines
In a DC machine the armature mmf is

 rotating with respect to field poles.
  stationary with respect to field poles.
  stationary with respect to armature.
  rotating with respect to field poles as well as armature.

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