## Law of ReflectionA light ray incident upon a reflective surface will be reflected at an angle equal to the incident angle. Both angles are typically measured with respect to the normal to the surface. This law of reflection can be derived from Fermat's principle.
| Index Reflection concepts Mirror concepts | ||

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## Fermat's Principle:ReflectionFermat's Principle: Light follows the path of least time. The law of reflection can be derived from this principle as follows:
This derivation makes use of the calculus of maximum-minimum determination, the derivative of a square root, and the definitions of the triangle trig functions.
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## Fermat's Principle and RefractionFermat's Principle: Light follows the path of least time. Snell's Law can be derived from this by setting the derivative of the time =0. It shows how the refraction of light at an interface depends upon the indices of refraction. This derivation makes use of the calculus of maximum-minimum determination and the definitions of the triangle trig functions.
| Index Reference Meyer-Arendt | ||

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