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

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

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

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