Electrical Machines
An IM cannot run at synchronous speed because

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

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Electrical Machines
The introduction of interpoles in between the main poles improves the performance of a dc machine, because

 a counter-emf is induced in the coil undergoing commutation
 the flux waveform is improved with reduction in harmonics
 the inequality of air-gap flux on the top and bottom halves of the armature is removed
 the interpoles produce additional flux to augment the developed torque

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