Shine unpolarized light on flat glass — is there an angle where the reflection vanishes for one polarization, and what does that reveal?
▶ Launch the interactive simulationSweep the incidence angle θᵢ for unpolarized light hitting flat glass and split the reflected beam with the Fresnel equations into its s- and p-polarized parts; locate the angle where the p-reflectance R_p falls to zero, and read the refractive index n = tan θ_B off that null.
Brewster's law — the p-reflectance hits EXACTLY zero at θ_B = arctan(n₂/n₁) ≈ 56.3° for glass, so the light reflected there is 100% s-polarized (the reflected and refracted rays come off perpendicular). Recovering n = tan θ_B from the R_p null is why polarized sunglasses kill glare and why laser cavities use Brewster windows. The polarization branch of the optics arc, after Snell, TIR, mirage and the rainbow.