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

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Electrical Machines
For an ideal transformer the winding should have

 equal resistance on primary and secondary side
 maximum resistance on primary side and least resistance on secondary side
 no ohmic resistance on either side
 minimum resistance on primary side and maximum resistance on secondary side

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