Fermat’s principle: The light ray always travels in a path which needs shortest possible time to cover distance between two points. This principle has lot of importance on optics.
This is used in
1. Laws of reflection (i.e., angle of incidence = angle of reflection)
2. Laws of refraction (Snell’s law)
3. To derive refractive index of a medium.
4. To derive refractive index of glass slab. So, I appreciate the Fermat’s principle.
