Task id16303

Why do Newton's rings form only due to the interference of rays 2 and 3, reflected from the air gap between the lens and the glass (Fig.), and ray 4, reflected from the flat face of the lens, does not affect the nature of the interference pattern? Assuming that monochromatic light falls normally, calculate the radii of Newton’s rings if the radius of curvature of the lens is known (in the figure, the path of rays 4, 2, 3 is slightly distorted so that it is better visible which rays we are talking about).