Electrical Machines
In DC generators brushes are used for

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

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Electrical Machines
Skewing of the rotor in a 3 - Φ squirrel cage induction motor reduces

  noise, parasitic torque, starting torque and pull out torque.
  noise and pullout torque, but increase parasitic and starting torque.
  noise and parasitic torque, but increase starting and pull-out torque.
  noise, parasitic and starting torque, but increase pull out torque.

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