The figure below shows a lens with radius of curvature R lying on a flat glass plate and illuminated from above by light with wavelength λ. This photo, taken from above the lens, shows that circular interference fringes (called "Newton's rings") appear, associated with the variable thickness d of the air film between the lens and the plate. The radius of curvature R of the lens is 5.0 m and the lens diameter is 19 mm.
(a) How many bright rings are produced? Assume that λ = 568 nm.
(b) How many bright rings would be produced if the arrangement were immersed in water (n = 1.33)?
maxima in thin film interference: 2L=(m=.5)λ/n2
A of a circle = [tex]\pi[/tex]r2 ?
The Attempt at a Solution
it would seem as simple as solving the equation 2L=mλ/n2 for m when the length of the air between the curved glass and the flat glass is greatest, wouldn't that tell you how many rings you've gone through to get to the edge? But I cannot seem to figure out how large the space of air IS right at the edge....
I think one also needs to find out whether light reflected will tend to be put in phase or out of phase.