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 three times the original value
 changes to 1.5 times the original value
 changes to 0.5 times the original value

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Electrical Machines
With the increase in speed of DC motor

 Back emf falls and line current increase.
 Both back emf as well as line current increase.
 Both back emf as well as line current fall.
  Back emf increase but line current falls.

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