Question

sir i want to about michelson morely experiment.why this experiment was performed

Answer 1

You can drop the formalities, I'm no 'sir' ;)

The michelson-morely experiment was performed to show the existence of a medium through which light waves traveled. The hypothesized medium was called 'luminiferous aether', and they attempted to measure the speed of the earth relative to that aether by shining light perpendicular to, and parallel to, to direction that point of the earth was moving through space. The difference in time it takes light to travel each respective direction is then going to tell how fast that point on the earth is moving relative to the aether.

The result was that the speed of light was the same in all directions, which gave rise to much of the experimental basis for special relativity, and did away with the antiquated notion of the aether.