Electrical Machines
The synchronous speed of an induction motor will be increased by

  decreasing of frequency.
  increasing number of poles.
  increasing of frequency.
  speed can not be increased.

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

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

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