In the context of light rays, what is the definition of a 'normal'?

The definition of a 'normal' in the context of light rays is a line that is perpendicular to the surface at the point of incidence. When light rays strike a surface, such as a mirror or a lens, understanding the orientation of the normal line is essential for analyzing how the light will reflect or refract at that surface. The normal serves as a reference line from which angles of incidence and reflection can be measured, following the laws of reflection and refraction, such as Snell's law.

This concept is crucial in optics because it helps clarify how light behaves when encountering different materials, enabling predictions about the angles at which light will travel after interacting with surfaces. Recognizing this relationship allows for improved understanding of phenomena like mirroring effects, bending of light, and other optical behaviors.