Electrical Machines
In a DC machine the armature mmf is

 rotating with respect to field poles.
  rotating with respect to field poles as well as armature.
  stationary with respect to armature.
  stationary with respect to field poles.

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Electrical Machines
Flashing the field of DC generator means

 increasing flux density by adding extra turns of winding.
  making the magnetic losses forces parallel.
  neutralising residual magnetism.
  creating residual magnetism by a DC source.

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