1. When a plano convex lens of large radius of curvature is placed on a glass plate, an air film is formed between the lower surface of the lens and upper surface of the plate.
2. The thickness of the film gradually increases from the point of contact outwards.
3. If monochromatic light is allowed to fall normally on this film, a system of alternate bright and dark concentric rings, with center dark is formed in the air film.
4. These rings were first studied by Newton and hence they are known as Newton's ring .
5. They can be seen through a low power microscope focused on the film.
6. Newton's rings are formed as a result of interference between the waves reflected from the top and bottom surface of the air film forced between the lens and the plate.
Let ρ be radius of a Newtons ring corresponding to the constant film thickness t.
Thus proved that the diameter of nth dark rings are proportional to square root of natural numbers.