Electrical Machines
Interpoles in a DC motor must be

 Series excited and should have the same polarity as that of the ahead 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.
 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.

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Electrical Machines
In a DC machine, for the same value of φ, Z and N; which one of the following statements is correct?

 Armature emf is less with wave winding than with lap winding.
  Armature emf is more with wave winding than with lap winding.
 Armature emf is same as long as the flux density in the air gap remains the same.
 Armature emf depends on weather the machine is running as a motor or generator.

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