Past exam of the optics and electrodynamics course of the University of Cambridge / 2012 / Paper 1 / 1 / a / Solution

The electric field of the reflected beam is perpendicular to the vertical plane of incidence, hence parallel to the water surface. At Brewster's angle the reflected p-polarization amplitude vanishes; only the s-polarization component remains. For incidence from air, approximated by refractive index one,Incidence is measured from the surface normal, whereas solar elevation is measured from the horizontal. The Brewster solar elevation is thereforeThis assumes an ideally flat, transparent, nonmagnetic interface; ripples, absorption and diffuse light would spoil complete polarization.