Electrical Machines
Consider the following statements regarding dc machines : 1. possible resistance of shunt-field winding is 1 Ω 2. possible resistance of series-field winding is 1 Ω 3. electrographite brushes are used for 230 V, 10 A machines 4. Copper-graphite brushes are used for 230 V, 10 A machines 5. Possible armature-circuit resistance is 1 Ω From these, the correct statements are

 2, 4 ,5
 1, 4
 2, 3 , 5
 1, 3, 5

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Electrical Machines
In a DC generator, the armature reaction results in

 demagnetization of centers of poles.
 magnetization of leading and demagnetization of trailing pole tip.
  demagnetization of leading & magnetization of trailing pole tip.
  magnetization of inter poles.

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