Electrical Machines
The oscillation in a synchronous motor can be damped out by

  providing damper bars in the rotor pole faces.
  oscillation cannot be damped.
  maintaining constant excitation.
  running the motor on leading power factors.

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Electrical Machines
For a given torque, reducing diverter resistance of a DC series motor causes

 decrease in speed demanding less armature current.
 increase in speed demanding more armature current.
 decrease in speed but armature current remains the same.
 increase in speed but armature currnet remains the same.

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