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.
  sR2 = X2.
  R2 = s2X2.

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Electrical Machines
In dc machines, the field system has to be provided on stator unlike synchronous machines Where in it could be on any member, because

 dc machines are comparatively low rating machines.
 commutator action is not possible otherwise
 it reduces field structure iron losses
 it gives more uniform air-gap flux distribution

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Electrical Machines
In a DC machine the armature mmf is

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

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Electrical Machines
In a step down transformer which one of the following statements is true?

 Secondary power is less than primary power.
 Secondary current is less than primary current.
 Number of secondary turns is more than that of primary.
  Number of secondary turns is less than primary turns.

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