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[Phys-l] question about total internal reflection



1. One implication of Snell's law is that for light incident on a boundary with a less dense medium, there must be a maximum angle where transmission can occur. This angle can be calculated by assuming that the refracted light makes a 90 degree angle with the normal in the second medium. But in fact, there is no refracted light -- if you place a sensor along the surface, you fail to detect light. The light has been internally reflected, as a well placed sensor would reveal.

2. This is not a sudden transition -- in fact, a fraction of the light is reflected at any angle of incidence. The reflected portion increases with angle of incidence and the transmitted portion decreases to zero..at that same critical angle? But why is that? It can't just be coincidence that the law that determines the fraction of light transmitted at a given angle from one medium to another happens to predict zero transmission at precisely the angle that Snell's law says it should.

Can anyone point me toward an explanation?

Thanks.