Electrical Machines
An IM cannot run at synchronous speed because

  rotor torque will not be produced.
  induction motor will become synchronous motor.
  none of above.
  air friction will prevent it.

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Electrical Machines
Interpoles in a DC motor must be

 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 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.
 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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