What is the definition of an incident ray?

An incident ray is defined as a ray that travels towards an object or a surface where an interaction, such as reflection or refraction, can occur. This ray is crucial in understanding how light behaves when it encounters different materials. When it strikes the surface, its properties change based on the medium it interacts with, leading to various optical phenomena.

In the context of light rays, the term "incident" specifically highlights the direction of travel toward a surface, which is essential when studying the angles of incidence and the subsequent behavior of light, such as how it reflects off surfaces or passes into different media. Understanding this concept is foundational in optics, as it informs the study of phenomena such as lenses, mirrors, and the behavior of light in various environments.