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

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

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Electrical Machines
With the increase in speed of a DC motor

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

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Electrical Machines
Ward-Leonard system for controlling the speed of a DC motor is used where

 All of above.
 Very fine speed control over the whole range from zero to normal speed is required.
 The speed in both the direction is required.
 The accuracy in speed control is required.

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