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.
$\frac{1}{9}$
9
$\frac{1}{3}$
3
Solution
For conducting sphere, $\mathrm{V}=\frac{\sigma \mathrm{r}}{\varepsilon_0}$ After contact, $\mathrm{V}_1=\mathrm{V}_2$ $\begin{aligned} & \sigma_1 r_1=\sigma_2 r_2 \\
& \frac{\sigma_1}{\sigma_2}=\frac{r_2}{\mathrm{r}_1} \\
& \frac{\sigma_1}{\sigma_2}=3 \end{aligned}$