Electrical Machines
Cogging of induction motor occurs at

 high voltage and when stator and rotor poles are equal.
 low voltage and when stator and rotor poles are not equal.
 high voltage and when stator and rotor poles are not equal.
 low voltage and when stator and rotor poles are equal.

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

 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
 the flux waveform is improved with reduction in harmonics
 a counter-emf is induced in the coil undergoing commutation

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