Electrical Machines
Under commutation results in

  sparking at the middle of the brush.
  sparking at the leading edge of the brush.
  sparking the trailing edge of the brush.
  no sparking.

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Electrical Machines
With the increase in speed of a DC motor

 back emf increases but line current falls.
 both back emf as well as line current fall.
 both back emf as well as line current increase.
 back emf falls and line current increases.

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