DC Generators
Carbon brushes are used in a dc machine because _______

None of the listed here
Carbon is cheap
Carbon lubricates and polishes the commutator
Contact resistance is decreased

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DC Generators
When two D.C. series generators are running in parallel, an equalizer bar is used

So that two similar machines will pass approximately equal currents to the load
To reduce the combined effect of armature reaction of both machines
To increase the series flux
To increase the speed and hence generated e.m.f.

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DC Generators
Inter-pole flux should be sufficient to

None of these
Neutralize the commutating self induced e.m.f.
Neutralize the armature reaction flux
Neutralize both the armature reaction flux as well as commutating e.m.f. induced in the coil

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