31. The diameters di and dk two bright Newton's rings are respectively 4.0 and 4.8 mm. Serial numbers of rings is not determined, but it is known that measured between the two rings are three bright rings. Rings were observed in the reflected light (λ = 500 nm). Find the radius of curvature R of the plano-convex lens, taken for the experience.

Detailed solution. Decorated in Microsoft Word 2003. (Target decided to use formula editor)