Newton's Rings and Radius of Curvature of a Glass Lens

Does the formula for radius of curvature of glass surface forming Newton's Rings depend on whether the central ring is bright or dark? If so, How?
- sankaracharyulu M G V (age 48)
KARAIKAL UT INDIA

The usual formula for the N^th bright ring of a plano-convex glass lens of radius R resting on a flat glass surface is r_N =  [(N-1/2) λR]^1/2 where λ is the wavelength of the light.   The inner ring is dark due to the destructive interference between the light reflected from the lens surface and the light reflected from the plane glass surface.   The minus sign comes from the relative indices of refraction at the air-glass interface.  Solving for R gives  R = r²_N/[(N-1/2) λ]². So you should count only the bright rings.    Check the Wikipedia article on Newton's rings for more details.

LeeH

(published on 03/28/2012)