where <math> \hat{\mathbf{n}} </math> is the unit normal vector at the interface pointing from medium 1 to towards medium 2,
<b>D(r)</b> = ε<b>E(r)</b> is the electric flux density, <b>E(r)</b> is the electric field vector, and ρ<sub>s</sub> is the surface charge density at the interface.