^Geometrical optics

Geometrical optics is also called ray optics. It treats propagation of light in terms of rays and is valid only if wavelength of light is much lesser than the size of obstacles. It deals with the following phenomena

1. rectilinear propagation (i.e. light propagates in a straight line, due to its small wavelength)
2. reflection (i.e. coming back in same medium on striking a shining surface)
3. refraction (i.e. change of speed on changing transparent medium)
4. dispersion (i.e. light splits up in to its constituent colours on changing transparent medium)
5. image formation ( i.e. intersection of two or light rays after undergoing reflection or refraction).