Let us imagine a surface, with X and Y axes on it and Z axis normal to it. well, the theory, (in my particular case, some article) says that S polarized light, propagating along the x-directioin possesses only electric field components, Ei, paralel to the surface (||y-direction), i.e. transversal electric waves have Ei=(0, Ey, 0), while P-polarized light has Ei=(Ex, 0, Ez). The question: I understand that S-polarized light, propagating along x-direction has only electric field components, Ei, paralel to the surface. Ei=(0, Ey, 0), since in case of s-polarization E is perpendicular to plane of incidence. Also I understand that P-polarized light, propagating in the same x-direction has Ez component, since in case of P-polarization E is in the plane of incidence. what I do not understand is, why p-polarized light has Ex component.