For a cell terminal $P.D.$ is $2.2\;V$ when circuit is open and reduces to $1.8\;V$ when cell is connected to a resistance of $R = 5\,\Omega $. Determine internal resistance of cell $(r)$ is then ........ $\Omega$
AIPMT 2002, Medium
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$E = 2.2\, V,$ $V = 1.8\, V, R = 5\,\Omega $
$r = \left( {\frac{E}{V} - 1} \right)\,R = \left( {\frac{{2.2}}{{1.8}} - 1} \right) \times 5$
==>$r = \frac{{10}}{9}\,\Omega $
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