Electrical Machines
Compensating windings are used in DC generators

  to provide path for the circulation of cooling air.
None of these
  mainly to reduce the eddy currents by providing local short circuit.
  to neutralize the cross magnetizing effect of the armature reaction.

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

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

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Electrical Machines
With the increase in speed of DC motor

 Back emf falls and line current increase.
 Both back emf as well as line current increase.
 Both back emf as well as line current fall.
  Back emf increase but line current falls.

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