Electrical Machines
The counter (or back) emf in a dc machine is 1. the same as generated emf in a dc motor 2. proportional to field flux and armature speed 3. not the same as generated emf in a dc motor 4.inversely proportional to field flux 5. proportional to number of armature conductors 6. constant from no load to full load From these, the correct answer is

 2, 3, 6
 1, 2, 5
 2, 4, 5, 6
 3, 4, 5

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Electrical Machines
Flashing the field of DC generator means

 increasing flux density by adding extra turns of winding.
  making the magnetic losses forces parallel.
  creating residual magnetism by a DC source.
  neutralising residual magnetism.

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