Electrical Machines
Commutator in DC generator is used for

 increase efficiency
 collecting of current
 reduce losses
 convert AC armature current in to DC

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Electrical Machines
With the increase in speed of a DC motor

 both back emf as well as line current fall.
 back emf falls and line current increases.
 both back emf as well as line current increase.
 back emf increases but line current falls.

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