Two sources of equal $emf$ are connected to an external resistance $R$. The internal resistances of the two sources are ${R_1}$ and ${R_2}\,({R_2} > {R_1})$. If the potential difference across the source having internal resistance ${R_2}$ is zero, then
AIEEE 2005,AIIMS 2008, Diffcult
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(d) $i = \frac{{2E}}{{R + {R_1} + {R_2}}}$
From cell $(2)$ $E = V + i{R_2} = 0 + i{R_2}$
$==>$ $E = \frac{{2E}}{{R + {R_1} + {R_2}}} \times {R_2}$
$==>$ $R = {R_2} - {R_1}$
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