Three plano-convex lenses A, B, and C are combined in pairs to form Newton's ring interference setups. Monochromatic light of wavelength lambda = 600 nm is incident normally. When A and B are combined (figure i), the 10th dark ring has radius r_AB = 4.0 mm. With B and C (figure ii), r_BC =

Question

Three plano-convex lenses A, B, and C are combined in pairs to form Newton's ring interference setups. Monochromatic light of wavelength lambda = 600 nm is incident normally. When A and B are combined (figure i), the 10th dark ring has radius r_AB = 4.0 mm. With B and C (figure ii), r_BC = 4.5 mm. With C and A (figure iii), r_CA = 5.0 mm. Which statement(s) about the radii of curvature are correct?

Accepted Answer

Radius of curvature of lens B is approximately 4.64 m.. rₙ² = n*lambda*R_eff where 1/R_eff = 1/R1 + 1/R2. Let a = 1/R_A, b = 1/R_B, c = 1/R_C. Then r_AB²/(n*lambda) = 1/(a+b), etc. Solving gives R_A, R_B, R_C and option B (R_B ~ 4.64 m) is the correct one.

Solution

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