Electrical Machines
In shunt dc motor the direction of rotation of the motor will reversed. When

  either field terminals are reversed or armature terminals are reversed.
  only armature terminals are reversed.
  none of above.
  only field terminals are changed.

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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.
 Very fine speed control over the whole range from zero to normal speed is required.
 The accuracy in speed control is required.

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Electrical Machines
If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced by 50%, the maximum flux density will (assuming that the magnetic circuit remains unsaturated)

 changes to 0.5 times the original value
 remain the same as the original
 changes to three times the original value
 changes to 1.5 times the original value

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