References: Griffiths, David J. (2007), Introduction to Electrodynamics, 3rd Edition; Pearson Education – Chapter 9, Post 36.
Here’s another simple example of the transmission coefficient for waves passing from medium 1 through medium 2 into medium 3. Suppose we have an aquarium filled with water (index of refraction ). Light from the aquarium passes (at normal incidence) through a sheet of glass () and into air ().
The transmission coefficient is given by
The maximum is when the sine is zero:
It doesn’t matter much what the frequency of the light is or how thick the glass is; most of the light makes it through in any case. Since 1 is symmetric in and a fish inside the aquarium can see out as easily as we can see in.