A Newton's rings apparatus is to be used to determine the radius of curvature of a lens.

Question:

A Newton's rings apparatus is to be used to determine the radius of curvature of a lens. The radii of the nth and (n + 20)th bright rings are measured and found to be 0.1,62 and 0.368 cm, respectively, in light of wavelength 546 nm. Calculate the radius of curvature of the lower surface of thelens.