Electrical Machines
The working principle of transformer depends on

 Newtons law.
 Coulombs law.
 Faradays law of electromagnetic induction.
 Amperes law.

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Electrical Machines
Short circuit test is performed on a transformer with a certain impressed voltage at rated frequency. If the short circuit test is now performed with the same magnitude of impressed voltage, but at frequency higher than the rated frequency then

 The magnitude will both increase.
 The magnitude of current will decrease but the power factor will increase.
 The magnitude of circuit as well as the power factor will decrease.
 The magnetude of current will increase, but power factor will decrease.

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Electrical Machines
In a DC generator, the armature reaction results in

  demagnetization of leading & magnetization of trailing pole tip.
  magnetization of inter poles.
 magnetization of leading and demagnetization of trailing pole tip.
 demagnetization of centers of poles.

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