The balancing length for a cell is $560 \;\mathrm{cm}$ in a potentiometer experiment. When an external resistance of $10 \;\Omega$ is connected in parallel to the cell, the balancing length changes by $60\; \mathrm{cm} .$ If the internal resistance of the cell is $\frac{\mathrm{N}}{10} \;\Omega,$ where $\mathrm{N}$ is an integer then value of $\mathrm{N}$ is
A$12$
B$10$
C$8$
D$14$
JEE MAIN 2020, Medium
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A$12$
a $\mathrm{r}=\mathrm{R}\left(\frac{\mathrm{x}-\mathrm{x}^{\prime}}{\mathrm{x}^{\prime}}\right)$
$=10 \times \frac{60}{500}$
$=12$
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