On transitory from a medium with one index of refraction to a medium with a different index of refraction light is typically both reflected and refracted. Under some conditions however all of the light is reflected-none of it gets by the interface. The phenomenon is described as Total Internal Reflection. In which situation if either can total internal reflection take place when light is already in the medium with the greater index of refraction and encounters the boundary between the two media or when light is already in the medium with the smaller index of refraction and encounters the boundary between the two media?

Ans:

The reality that the light has to be inside the medium with the larger index of refraction in order to experience total internal reflection is where total internal reflection gets its name. Consequently for instance in an experiment involving a prism if light is to experience total internal reflection at the surface of the prism the light has to be travelling inside the prism as it approaches that surface.