In the given circuit, an ideal voltmeter connected across the $10\,\Omega $ resistance reads $2\, V$. The internal resistance $r$, of each cell is ................... $\Omega$
JEE MAIN 2019, Medium
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$ R_{e q} =\frac{15 \times 10}{25}+2+2 r $
$ =8+2 r $
$i=\frac{3}{8+2 r}$
$2=\mathrm{i} \mathrm{R}_{\mathrm{eq}}=\frac{3}{8+2 \mathrm{r}} \times 6$
$16+4 r=18$
$\Rightarrow r=0.5\, \Omega$
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