Two identical cells send the same current in $2\,\Omega $ resistance, whether connected in series or in parallel. The internal resistance of the cell should be ............... $\Omega$
Medium
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In series , ${i_1} = \frac{{2E}}{{2 + 2r}}$
In parallel, ${I_2} = \frac{E}{{2 + \frac{r}{2}}} = \frac{{2E}}{{4 + r}}$
Since ${i_1} = {i_2}$ $ \Rightarrow $ $\frac{{2E}}{{4 + r}} = \frac{{2E}}{{2 + 2r}}$ $ \Rightarrow $ $r = 2\,\Omega $
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