DC Generators
The number of brushes in a commutator depends on

Voltage
Amount of current to be collected
Type of winding
Speed of armature

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DC Generators
While applying Fleming's right-hand rule to and the direction of induced e.m.f., the thumb points towards

Direction of induced e.m.f.
Direction of motion of conductor, if forefinger points along the lines of flux
Direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
Direction of flux

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