Electric field at a conducting plane from axial point charges ($E_z(0^{+})=-\frac{2}{4\pi {ϵ}_0}{\sum }_j{Q}_j/h_j^2$)

For point electric charges at heights $h_j>0$ on one normal above an infinite grounded conducting plane, the method of images places opposite image charges at $-h_j$. At the point directly below them, tangential electric fields cancel and normal components add, giving the displayed one-sided field. The electric field inside the metal is zero instead. The boundary jump is supported by induced surface charge.