Electrical Machines
A simple method of increasing the voltage of a DC generator is to

 increase the source frequency.
 increase the number of turns in armature coil.
  increase the speed of shaft rotation.
 increase the number of turns in field coil.

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Electrical Machines
In speed control of DC Series motor, speed lower than the rated speed can be obtained by

 Connecting an additional resistance in stator circuit.
 Connecting an additional resistance in the armature circuit.
 Any of the above.
 Connecting an additional resistance in the field circuit.

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