Electrical Machines
In a DC generator the emf generated by the armature is maximum when

  rate of change of flux is maximum.
 rate of change of flux is minimum.
 induced voltage is high.
 shaft rotation is high.

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Electrical Machines
Interpoles in a DC motor must be

 Shunt excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.

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