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 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

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Electrical Machines
Two 3-phase AC generators are such that one has twice the linear dimensions of the other. The field windings of each are excited to give identical sinusoidal air-gap flux density waveform. Both have the same number of stator slots and identical winding patterns. The conductor/slot in a big generator is K times that of the smaller one. The value of K to get equal no load voltage at same frequency is

 8.
  1/2.
 4.
 1/4.

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