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The brush potential of a separately exci...

The brush potential of a separately excited generator, when it is delivering 5 A is 125 V. When the generator dilivers 15 A, the potential difference across the brushes fall to 122 V. What are the induced e.m.f. and the resistance of armature ?

Text Solution

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Here, (i) `I = 5 A, V = 125 v`
As `V = E - 1 r :. 125 = E - 5 r`
(ii) When `I = 15 A, V = 12V :. 122 = E - 15 r`
Subtract (ii) from (i), `3 = 10 r, r = 0.3 Omega`
Form (i), `125 = E - 5 xx 0.3`
`E = 125 + 1.5 = 126.5 V`
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