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

 the flux waveform is improved with reduction in harmonics
 a counter-emf is induced in the coil undergoing commutation
 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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Electrical Machines
For a given torque, reducing diverter resistance of a DC series motor causes

 decrease in speed demanding less armature current.
 decrease in speed but armature current remains the same.
 increase in speed demanding more armature current.
 increase in speed but armature currnet remains the same.

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