Electrical Machines
Under commutation results in

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

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Electrical Machines
An ideal synchronous motor has no starting torque because

 rotor winding is highly reactive.
 relative velocity between the stator and rotor mmf’s is zero.
  relative velocity between stator and rotor mmf’s is not zero.
 rotor is made up of salient poles.

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