Electrical Machines
The magnetic field which initially induces emf in the armature in a self excited DC generator is because of

 armature reaction.
None of these
  permanent magnets.
  residual magnetism.

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Electrical Machines
In the 3-phase induction motor, the resultant flux is of a constant nature and is

 equal to φm, where φm is the maximum flux due to any phase
 3 times maximum value of flux due to any phase
 3/2 times maximum value of flux due to any phase
 1/2 times maximum value of flux due to any phase

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