Electrical Machines
The air gap between stator and the rotor of the 3 - φ induction motor is kept

  depends on the material of stator and the rotor.
  as small as possible.
  as wide as possible.
  air gap does not matter.

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

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

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

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