A resistance of $4\,\Omega $ and a wire of length $5\,m$ and resistance $5\,\Omega $ are joined in series and connected to a cell of $e.m.f.$ $10\, V$ and internal resistance $1\,\Omega $. A parallel combination of two identical cells is balanced across $300\, cm$ of the wire. The $e.m.f.$ $E$ of each cell is ........... $V$
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$E = x\,l = \frac{V}{l} = \frac{{iR}}{L} \times l$
$E = \frac{e}{{(R + {R_h} + r)}} \times \frac{R}{L} \times l$
$E = \frac{{10}}{{(5 + 4 + 1)}} \times \frac{5}{5} \times 3 = 3\,V$
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