Two metal spheres of radius $R$ and $3 R$ have same surface charge density $\sigma$. If they are brought in…

Two metal spheres of radius $R$ and $3 R$ have same surface charge density $\sigma$. If they are brought in contact and then separated, the surface charge density on smaller and bigger sphere becomes $\sigma_1$ and $\sigma_2$, respectively. The ratio $\frac{\sigma_1}{\sigma_2}$ is.
  1. $\frac{1}{9}$
  2. 9
  3. $\frac{1}{3}$
  4. 3

Solution

For conducting sphere, $\mathrm{V}=\frac{\sigma \mathrm{r}}{\varepsilon_0}$
After contact, $\mathrm{V}_1=\mathrm{V}_2$
$\begin{aligned}
& \sigma_1 r_1=\sigma_2 r_2 \\ & \frac{\sigma_1}{\sigma_2}=\frac{r_2}{\mathrm{r}_1} \\ & \frac{\sigma_1}{\sigma_2}=3
\end{aligned}$

Asked in: JEE Main 2025 (08 Apr Shift 2)

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