Elaboration of experimental results
polarization
At the border line of two dielectric materials we deal with partial reflection and refraction of light. When there is an angle of 90º between a reflected and refracted ray, reflected light becomes polarized linearly. An angle of incidence which meets that requirement is known as the Brewster's angle. Relation between the Brewster's angle and refraction index is the following:
It means that in our experiment we are not interested in a refracted ray, but in a reflected ray. So the thickness of dielectric from which a fully polarized ray is reflected is of no importance. Therefore, that method can be used to measure a refractive index for a non-transparent dielectric.