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

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Electrical Machines
When the supply terminal of a DC shunt motor are interchanged

 The direction of rotation will reverse.
 The motor will stop.
  The motor will run at its normal speed in the same direction as before.
 The motor will run much faster in the same direction.

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