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

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

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Electrical Machines
Due to magnetic saturation, the flux per pole in a DC machine without brush shift

 increases in generators but decreases in motor with load.
 decreases in generators and increases in motor with load.
  decreases in both generators and the motors with load.
 increases in both the generators and the motors with load.

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