Electrical Machines
The polarity of a DC generator can be reversed by

 increasing field current.
 reversing field electric current as well as direction of rotation.
 any of above.
 reversing the field current.

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Electrical Machines
With the increase in speed of a DC motor

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

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