Electrical Machines
In salient pole synchronous machine, if direct axis reactance and quadrature axis reactance is equal, then power developed due to reluctance is

 zero
 maximum
 any of the above
 infinite value

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Electrical Machines
Commutation in a DC machine may be explained as a process

  by which electric current in a coil is reversed.
 how alternate flux affects the main field flux.
 by virtue of which emf is induced in the armature conductors.
  in which magnetic field is set up.

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

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Electrical Machines
The speed of a DC series motor is

 Proportional to field current.
 Proportional to the armature current.
 Proportional to the square of the armature current.
 Inversely proportional to the armature current.

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