Electrical Machines
The residual magnetism of a self-excited dc generator is lost. To build up its emf again

 the armature connection must be reversed
 field winding must be excited by low voltage dc supply
 the field winding connection must be reversed
 the field winding must be replaced

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Electrical Machines
For a given torque, reducing divertor resistance of a DC series motor

  Increase in speed demanding more armature current.
  Decrease in speed demanding less armature current.
  Decrease in speed but armature current remains the same.
  Increase in speed but armature currnet remains the same.

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