Geometrical optics, also known as ray optics, is one of the two main branches of optics, the other being physical optics.
Geometrical optics is based on the assumption that light travels as a straight line and is useful in explaining various optical phenomena, including reflection and refraction, in simple terms.
Geometrical optics is a useful tool in analyzing the behaviour of optical systems, including the image-forming process and the appearance of aberrations in systems containing lenses and prisms.
The underlying assumptions of geometrical optics include that light rays:
Propagate in straight-line paths when they travel in a uniform medium.
Bend, and in particular, refract, at the interface between two dissimilar media.
Follow curved paths due to the varying refractive index of the medium.
May be absorbed as photons and transferred to the atoms or molecules of the absorbing material, causing the absorbing material to heat up or emit radiation of its own.