Electrical Machines
Which of the following is done in speed control of DC motor by field flux control?

 Inserting an additional resistance in the field circuit.
 Any of above.
 Inserting an additional resistance in the armature circuit.
 Inserting resistance to armature circuit and field circuit.

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Electrical Machines
Commutation in a DC machine may be explained as a process

 by virtue of which emf is induced in the armature conductors.
  by which electric current in a coil is reversed.
 how alternate flux affects the main field flux.
  in which magnetic field is set up.

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