Question

Fermat principle states that light takes the quickest path .please tell me how light knows which path is quickest??

Answer 1

As the reader may have noted, a noncalculus proof of the
fact that Fermat’s principle implies Snell’s law is bound to
require some effort. The need to surmount these difficulties
was one of the driving forces behind the early development
of calculus by Gottfried Leibniz. In fact, the interest gener-
ated by the phenomenon of refraction led Leibniz to discuss
it in 1684 in the first paper ever published on calculus.14 The
usual calculus-based proof is certainly impressive, and
should be taught to undergraduates, but it does not convey a
sense of the difficulties that Fermat had to surmount.The principle that the path taken between two points by a ray of light is the path that can be traversed in the least time. Light is always in a hurry and so normally a straight path tends to be the quickest path between two points A and B. So light is also said to be a beam of ray.