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Reflection and Refraction 
Reflection and Refraction are two wave phenomena that cause a change in direction of a wavefront at an interface between two different media. In general, a light wave is partially refracted and partially reflected when it passes from one medium to another at any angle other than 0° from the normal.
with the angle of incidence and the angle of reflection .
Refraction: The direction of the propagating wave changes according to the refractive indices.
with the angle of incidence , the angle of refraction , the refractive indices and .
The refractive index of a material
with is the material’s relative permittivity, and is its relative permeability.
Total Internal Reflection
The total reflection will happen at the critical angle
where is the critical angle, and are the refractive index.
- If , the ray will split; some of the ray will reflect
- If , the entire ray reflects from the boundary.
Light that is reflected at Brewster’s angle