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Lets put these equations to work and figure out something practical. Consider light reflecting off a surface, such as the road in front of you when you aredriving a car. The light hitting the road surface can have any polarization but that will be some addition of light that has and to the plane of incidence. From and we see there is an angle where there is no and only light, namely or Now we can use Snell's law rewritten as and multiply both sides to get which can only be true if In this case Snell's law can be written The angle that gives this effect is known as Brewster's angle At this angle light is completely polarized, it only has to the plane of incidence (or parallel to the surface). Thus the glare you get from reflected light tends to be polarized in this way. In 1929 Edwin Landinvented a method for making celluoid filters to filter out light with given polarizations. He then manufactured sunglasses with these polarizers lined upto filter out the light and thereby reduce glare.
Look at the Fresnel equations again and examine what happens when approaches 90 degrees. The reflection approaches 1 (ignore the signs) Thus at Glancing incidence you get lots of reflection. In fact X-ray telescopes usethis to focus the x-rays onto their detector.
Another effect, if then there is an angle of incidence beyond which light is only reflected. That is the angle where degrees. The critical angle at which this occurs is
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