wave equations

Electromagnetic Nature of Light — A brief history of light.

Let us begin this lecture which has roughly two parts;

1. the history of light and its understanding through the centuries

and

2. the electromagnetic nature of light

A brief history of light

Various optical devices and optical phenomena have been known since close to 4000 years. The optical devices of ancient time includes mirrors, burning glasses, lenses and other magnifying devices.

Accordingly various properties and laws of light were understood and developed since these times. E.g.

a. light was understood to propagate rectilinearly and 

b. light was understood to reflect and refract.

Least action principle and principle of equivalence …

This article is written in the flow of my intuition which is in a chronological order without any flip-flops. So first I came up with the idea Principle of equivalence means nature of potential energy and kinetic energy are same hence they are equivalents not gravitational mass and kinematic mass as represented through all texts [read other articles linked in this article for this idea] Then I came with the idea it actually follows from Prinicple of Least action in a round about way [which could be spurious and incorrect but leads to the answer] and in a direct and simple way in two lines.