Electrical Machines
To achieve spark less commutation brushes of DC generator are rocked ahead so as to bring them

 in magnetic neutral axis.
 just ahead of magnetic neutral axis.
None of these
 just behind the magnetic neutral axis.

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Electrical Machines
Slip speed is the

  difference of actual rotor speed and synchronous speed.
  difference of synchronous speed and actual rotor speed.
  half of the sum of synchronous and rotor speeds.
  sum of synchronous and rotor speeds.

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