What is Newton's Ring? How it works & usages?

Newton's rings are ring-shaped interference maximum and minimum seeming around the point of tang ency of a marginally curved convex lens and a plane-parallel plate as light permits through the lens and plate.

The interference pattern in the form of rings happens when light is mirrored from two surfaces, one of which is flat, and the other has a moderately large radius of curvature and comes into contact. If a beam of homo chromatic light is event on such a system in a direction erect to the plane surface, then the light waves reflected from each of these surfaces interfere with each other. The interference pattern shaped in this way comprises of the surfaces of a dark circle witnessed in the place of contact and the neighboring light and dark concentric rings surrounding it.