The experimental set-up for producing Newton's ring is shown in fig. (A). A plane-convex lenses L of large radius of curvature with its convexities is placed on a plane glass plate P. When light from an extended monochromatic source is allowed to fall on plane glass plate G inclined at an angle of 45 degree to the incident beam, it reflects incident light beam in vertically downward direction on the system (Plano-convex lens L + Plane glass plate P). The light waves reflected form the top and bottom surfaces of the air film produces interference fringes. These interference fringes (rings) may be seen by using a low power microscope.