Reflection and Refraction on a Flat Surface between Two Different Materials
When a ray of light hits the surface between two different materials, part of it is reflected and part of it is refracted through the second material. Call the angle between the incoming ray and the normal to the surface. The angle of reflection is , while the angle of refraction is , satisfying , where and are the ratios between the speed of light in a vacuum and in the materials, and . There is no reflected ray when .
If the angle is greater than , there is total reflection, which means that the ray does not cross the surface. (This is explicitly indicated in the panel on the right as " does not exist".)