Electrical Machines
To avoid formation of grooves in the commutator

  the brushes of opposite polarity should track each other.
None of these
  brush position has no effect on the commutator grooving.
 the brushes of same polarity should track each other.

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Electrical Machines
If two 8-pole dc machines of identical armature sare wound, one with lap winding and the other with wave winding, then

 lap-wound machine will have more rated voltage and less current
 lap-wound machine will have more rated voltage and more current
 wave-wound machine will have more rated current and more voltage
 wave-wound machine will have more rated voltage and less current

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