Electrical Machines
In a DC machine the armature mmf is

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

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Electrical Machines
In a dc generator operating on load with its brushes on the geometrical neutral axis (GNA), the magnetic neutral axis (MNA) is shifted in the direction of rotation. Now, if the brushes are given a lead of 90° (electrical), then the MNA will

 shift forward by less than 90°
 shift forward by 90°
 coincide with the GNA
 shift forward by more than 90°

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