Energy stored inthe capacitor $\mathrm{U}=\frac{1}{2} \mathrm{CV}^{2}$

When a dielectric slab of dielectric constant

$\mathrm{K}$ is introduced between the plates of the

condenser, then $\mathrm{C} \longrightarrow \mathrm{KC}$

So energy stored will become $K$ times.

since $Q=C V,$ So $Q$ will become $K$ times

$\therefore $ Surface charge density

$\sigma^{\prime}=\frac{\mathrm{KQ}}{\mathrm{A}}=\mathrm{K} \sigma_{0}$