Electrical Machines
Armature reaction in a DC machine

 is in the same direction as the main poles.
 makes an angle with the main pole axis which is load dependent.
 is in direct opposition to the main poles.
  makes an angle of 90° with the main pole axis.

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Electrical Machines
In a loaded DC generator, if the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will

 improve with rise in terminal voltage.
 improve with fall of terminal voltage.
 deteriorate with rise in terminal voltage.
 deteriorate with fall of terminal voltage.

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