The figure (a) shows a lens with radius of curvature R = 139 cm lying on a flat

Question

The figure (a) shows a lens with radius of curvature R = 139 cm lying on a flat glass plate and illuminated from above by light with wavelength λ = 600 nm. Figure (b) (a photograph 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. Find the radii r of the interference maxima assuming r/R << 1.

A) What is r for the first ring around the central spot?

B) What is r for the second ring around the central spot?

Explanation / Answer

rn=[(N-0.5)*lambda*R)^1/2

A)r1=((1-0.5)*600*10^-9*1.39)^(1/2)

=6.46*10^-4 m

B)r2=((2-0.5)*600*10^-9*1.39)^(1/2)

=1.118*10^-3 m

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