Determine the radius of Newton's second dark ring in reflected light, if the device, consisting of a plano-convex lens with a radius of curvature R = 8 m and a flat glass plate, was illuminated by monochromatic light with a wavelength of 640 nm.

A detailed solution with a brief note of the conditions, formulas and laws used in the solution, the derivation of the calculation formula and the answer.
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