A beam of unpolarized light in air strikes a flat piece of glass at an angle of 57.3e . If the reflected beam is completely polarized, what is the index of refraction of the glass?

Huygen's principle: Every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself. The new wave front is the envelope of all the wavelets - that is, tangent to all of them.