Two cells when connected in series are balanced on $8\;m$ on a potentiometer. If the cells are connected with polarities of one of the cell is reversed, they balance on $2\,m$. The ratio of $e.m.f.$'s of the two cells is
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(b) $\frac{{{E_1}}}{{{E_2}}} = \frac{{{l_1} + {l_2}}}{{{l_1} - {l_2}}} = \frac{{(8 + 2)}}{{(8 - 2)}} = \frac{5}{3}$
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