A plano-convex glass lens with curvqature radius of spherical surface `R = 12.5 cm` is pressed against a glass plate. The diameters of the tenth and fifteenth dark Newton's rings in reflected light are equal to `d_(1) = 1.00 mm` and `d_(2) = 1.50 mm`. Find the wavelength of light.

Explanation

From the formula for Newton's rings we derive for dark rings
`(d_(1)^(2))/(4) = k_(1)R lambda, (d_(2)^(2))/(4) = k_(2) R lambda`
so `(d_(2)^(2) - d_(1)^(2))/(4(k_(2) - k_(1))R) = lambda`
Substituating the values, `lambda = 0.5 mu m`.