To study interference in thin film of nonuniform thickness (wedge shaped film). The interference pattern consists of alternate dark and bright concentric.circular fringes.This pattern was first time observed by Newton.It can be used to determine the radius of curvature of the lens,even refractive index of the liquid can be determined by Newton's rings.In above experiment,by measuring the diameters of dark rings, radius of curvature of a plano convex lens is calculated.