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

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Electrical Machines
With the increase in speed of a DC motor

 back emf falls and line current increases.
 back emf increases but line current falls.
 both back emf as well as line current increase.
 both back emf as well as line current fall.

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Electrical Machines
A 3-φ alternator has negligible stator resistance. A short circuit test is conducted on this alternator. At a particular speed, a field current of If1 is required to drive the rated armature current. If the speed of the alternator is reduced to half, the field current required to maintain rated armature current

 Woud be equal to 2If1.
 Would be equal to If1/2.
 Would be equal to If1.
  Cannot be predicted due to insufficient data.

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