JEE MAIN - Physics (2021 - 17th March Evening Shift - No. 8)
Two cells of emf 2E and E with internal resistance r1 and r2 respectively are connected in series to an external resistor R (see figure). The value of R, at which the potential difference across the terminals of the first cell becomes zero is
_17th_March_Evening_Shift_en_8_1.png)
r1 $$-$$ r2
$${{{r_1}} \over 2} - {r_2}$$
$${{{r_1}} \over 2} + {r_2}$$
r1 + r2
Explanation
_17th_March_Evening_Shift_en_8_2.png)
$$l = {{3E} \over {R + {r_1} + {r_2}}}$$
_17th_March_Evening_Shift_en_8_3.png)
$${V_A} = {V_B}$$
$$2E = i\,{r_1}$$
$$2E = {{3E} \over {R + {r_1} + {r_2}}}{r_1}$$
$$2R + 2{r_1} + 2{r_2} = 3{r_1}$$
$$R = {{{r_1}} \over 2} - {r_2}$$
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