Electrical Machines
Armature reaction in a DC machine

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

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Electrical Machines
Cogging and crawling are phenomena associated with

 the former during starting and the latter at a fraction of its rated speed.
 cage induction machines and they are essentially the same.
 the former at a fraction of its rate speed and the latter during starting.
 any of the above.

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