Electrical Machines
For a given torque, reducing divertor resistance of a DC series motor

  Increase in speed demanding more armature current.
  Decrease in speed but armature current remains the same.
  Increase in speed but armature currnet remains the same.
  Decrease in speed demanding less armature current.

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Electrical Machines
In a DC machine

 current and emf in armature are alternating.
 emf in armature conductors and at the terminals is alternating.
 current and emf at the terminals are alternating.
 current and emf in armature are unidirectional

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Electrical Machines
Cogging and crawling are phenomena associated with

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

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