#### Reflection and Refraction

The first equality in Eq.(C.56) implies that the
*angle of incidence equals angle of reflection:*

We now wish to find the wavenumber in medium 2. Let denote the phase velocity in wave impedance :

*refraction*of the plane wave as it passes through the impedance-change boundary. The refraction angle depends on ratio of phase velocities . This ratio is often called the

*index of refraction*:

*Snell's Law*(of refraction).

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Reflection Coefficient