Electrical Machines
Copper brushes in DC machine are used

 where high voltage and low current.
 where low voltage and high currents are involved.
None of these
 in both of above cases.

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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, 3, 5
 1, 4
 2, 3 , 5

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