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Refraction and Reflection
Excerpt from Field Guide to Geometrical Optics
Snell's law of refraction:
The incident ray, the refracted ray and the surface normal are coplanar.
When propagating through a series of parallel interfaces, the quantity nsinθ is conserved.
Law of reflection:
The incident ray, the reflected ray and the surface normal are coplanar.
Reflection equals refraction with n2 = –n1.
At the critical angle, the angle of refraction θ2 equals 90°.
The reflectance ρ of an interface between n1 and n2 is given by the Fresnel reflection coefficients. At normal incidence with no absorption,