Electrical Machines
In case of a dc motor the ratio Eb / E is indicative of

  ratio of starting to running torque.
  ratio of starting to running current.
  ratio of input to output voltage.
  efficiency.

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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 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.
 Shunt 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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