Electrical Machines
A DC series motor is running at rated speed without any additional resistance in series. If an additional resistance is placedin series, the speed of motor

 Increases.
 Remains unchanged.
 Oscillates around the rated speed.
  Decreases.

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

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