Asked by jayy

What the law of reflection

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Answered by GPT-5 mini AI
The law of reflection states:

- The angle of incidence equals the angle of reflection: θi = θr.
- Both angles are measured from the normal (a line perpendicular to the surface) at the point where the ray hits.
- The incident ray, the reflected ray, and the normal all lie in the same plane.

In words: when a light ray (or any wave) strikes a smooth surface, it bounces off so that the incoming angle to the perpendicular equals the outgoing angle.

Simple ASCII sketch:

incident ray
\
\ θi
\ \
----------•---- surface
/ /
/ θr
/ reflected ray

(• is the point of contact; the normal is a vertical line at that point; θi and θr are measured between each ray and the normal.)

Notes:
- For a flat (plane) mirror, this gives a virtual image the same distance behind the mirror as the object is in front.
- For rough surfaces (diffuse reflection), microscopic facets reflect in many directions, so there is no single reflected angle for the whole surface.
- The law can be derived from Fermat’s principle (light takes the path of least time) or from electromagnetic boundary conditions.