Electrical Machines
Commutation in a DC machine may be explained as a process

  by which electric current in a coil is reversed.
  in which magnetic field is set up.
 by virtue of which emf is induced in the armature conductors.
 how alternate flux affects the main field flux.

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

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