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Question
A cell of emf E and internal resistance r is connected across an external resistance R. Plot a graph showing the variation of P.D. across R, versus R.
Solution
We know that `I = E/(R + r)` and `V = IR`.
So `V = (ER)/(R + r)` .....(I)
`V = E/(1 + r/R)` ......(II)
Here E and r are constants.
So `V oo 1/(1 + r/R)` (from (II)
And `V oo R` (from I)
With increase in R, P.D. across R is increased up to maximum value E.
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