A plano-convex lens with radius of curvature R = 3.8 m is in contact with a flat plate of glass. A light source and the observer's eye are both close to the normal, as shown in the figure below. The radius of the 49th bright Newton's ring is found to be 9.0 mm. What is the wavelength of the light produced by the source? nm R

A plano-convex lens with radius of curvature R = 3.8 m is in contact with a flat plate of glass. A light source and the observer's eye are both close to the normal, as shown in the figure below. The radius of the 49th bright Newton's ring is found to be 9.0 mm. What is the wavelength of the light produced by the source? nm R