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.
  in which magnetic field is set up.
 how alternate flux affects the main field flux.

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Electrical Machines
Consider the following statements : Interpoles in dc machines 1. reducearmature reaction effects in the interpolar region 2. have the same dimension as main polls 3. have their windings connected in series with the armature 4. have same number of turns as the armature 5. have the polarity same as that of the main pole ahead in a motor From these, the correct statements are

 1, 3 and 5
 1, 2, 3 and 5
 1, 2 and 3
 1 and 3

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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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