Electrical Machines
If the field circuit of a DC shunt motor is opened

  The motor will attain dangerously high speed.
 The armature current will reduce.
 The speed of motor will be reduced.
 DC Shunt Motor

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

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

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

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