Electrical Machines
Under commutation results in

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

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Electrical Machines
Interpoles in a DC motor must be

 Shunt excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.

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