Electrical Machines
With the increase in speed of a DC motor

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

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Electrical Machines
Commutation in a DC machine may be explained as a process

 how alternate flux affects the main field flux.
 by virtue of which emf is induced in the armature conductors.
  in which magnetic field is set up.
  by which electric current in a coil is reversed.

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