Geometric optics describe how light moves in form of rays. When an object is dropped in the water two-dimensional waves are created on the surface. Light is emitted in all directions of the three-dimensional world. The waves produced are spherical and a ray diagram is formed, the same way light travels through mirrors and lenses.
“Geometrical optics, or ray optics, describes light propagation in terms of rays. The ray in geometric optics is an abstraction useful for approximating the paths along which light propagates under certain circumstances.
The simplifying assumptions of geometrical optics include that light rays:
- propagate in straight-line paths as they travel in a homogeneous medium
- bend, and in particular circumstances may split in two, at the interface between two dissimilar media
- follow curved paths in a medium in which the refractive index changes
- may be absorbed or reflected.
Geometrical optics does not account for certain optical effects such as diffraction and interference. This simplification is useful in practice; it is an excellent approximation when the wavelength is small compared to the size of structures with which the light interacts. The techniques are particularly useful in describing geometrical aspects of imaging, including optical aberrations.” https://en.wikipedia.org/wiki/Geometrical_optics