DC Generators
In a commutator

Mica and copper are equally hard
Copper is harder than mica
None of the listed here
Mica is harder than copper

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

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