DC Generators
The rapid wear of brushes takes place due to

Excessive spring pressure
Rough commutator bars
All of these
Abrasion from dust

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DC Generators
In D.C. generators the polarity of the interpoles

Is the same as that of the immediately preceding pole
Is opposite to that of the main pole ahead
Is neutral as these poles do not play part in generating e.m.f.
Is the same as that of the main pole ahead

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