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)

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

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Electrical Machines
For a given torque, reducing divertor resistance of a DC series motor

  Decrease in speed demanding less armature current.
  Increase in speed demanding more armature current.
  Increase in speed but armature currnet remains the same.
  Decrease in speed but armature current remains the same.

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