Electrical Machines
The polarity of a DC generator can be reversed by

 any of above.
 reversing field electric current as well as direction of rotation.
 increasing field current.
 reversing the field current.

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Electrical Machines
Cogging of induction motor occurs at

 high voltage and when stator and rotor poles are equal.
 high voltage and when stator and rotor poles are not equal.
 low voltage and when stator and rotor poles are equal.
 low voltage and when stator and rotor poles are not equal.

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Electrical Machines
The coil spam

 can never be equal to pole pitch.
  may or may not be exactly equal to people pitch.
 none of above.
 must be exactly equal to people pitch.

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