- A thin wedge-shaped air film is created by placing a Plano-convex lens on a flat glass plate. A
monochromatic beam of light is made to fall at almost normal incidence on the arrangement. Ring
like interference fringes are observed in the reflected light. The diameter of rings is
measured both in the absence and presence of water in the wedge.
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Radius of curvature of Plano-convex lens depends on the wavelength (\(\lambda\)), diameter of bright
fringe (\(D\)) and order of the fringe and refractive index (\(\mu\))
$$R=\frac{μ(D_{n+m}^2-D_{n}^2)}{4mλ}$$