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## Homework Statement

Newton's rings can be seen when a planoconvex lens is placed on a flat glass surface. For a particular lens with an index of refraction of n= 1.51 and a glass plate with an index of n= 1.78, the diameter of the third bright ring is 0.760 mm.

If water (n= 1.33) now fills the space between the lens and the plate, what is the new diameter of this ring?

## Homework Equations

r

_{N}= [(N-0.5)λR]

^{1/2}

r=radius of N

^{th}bright ring

N=ring number

λ=wavelength of light that passes through the glass

R=radius of curvature of the lens

## The Attempt at a Solution

If I was given a value for λ for the wavelength of light, I know I could simply plug in everything to find the radius of curvature of the planoconvex lens, then divide λ by 1.33 and solve for the new r

_{3}, but with the given data I am not sure how to find the wavelength of light, or if there is some other way to go about solving this problem.