$$\require{cancel}$$
$E_{n}=|\overrightarrow{\mathrm{E}}|=\frac{\sigma_{t}}{\epsilon_{0}}=\frac{1}{\epsilon_{0}}\left(\sigma_{f}+\sigma_{b}\right), \label{2.23}$
where $$σ_f$$ is a free surface charge density on the conducting body, and $$σ_b = −P_n$$ is a bound surface charge density due to a discontinuity in the normal component of $$\vec P$$ if the conductor is in contact with a dielectric material.