A piece of curved glass has a radius of curvature of r = 10.2 m and is used to f

Question

A piece of curved glass has a radius of curvature of r = 10.2 m and is used to form Newton's rings, as in the figure below. Not counting the dark spot at the center of the pattern, there are one hundred dark fringes, the last one being at the outer edge of the curved piece of glass. The light being used has a wavelength of 423 nm in vacuum. What is the radius R of the outermost dark ring in the pattern? (Hint: Note that r is much greater than R, and you may assume that tan ? = ? for small angles, where ? must be expressed in radians.)
___________ m

Explanation / Answer

The radius of nth ring is given by

r_n^2 = n ( lamda) R

           =100 ( 423 * 10 ^-9 m) 10.2 m

r_n =sqrt 100 ( 423 * 10 ^-9 m) 10.2 m

        =0.02077 m

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