Electrical Machines
In DC generators brushes are used for

 collecting of voltage
 reduce eddy current loss
 collecting of current without any sparkings
 convert ac armature current in to dc

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Electrical Machines
Two of supply terminals to a 3 - Φ induction motor get interchanged during re-connection after normal maintenance. When switched on the supply, the motor will

  get heated and damaged.
  rotate in the same direction as before maintenance.
  not start at all.
  rotate in direction opposite to that before maintenance.

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