Subject: Applied Physics 2

Topic: Interference And Diffraction

Difficulty: Medium

Diameters of two consecutive Newtons rings in the reflected light of $\lambda$ = 5890 $\mathring{A}$ are found to be 2.00 & 2.02 cm. Determine the radius of curvature of the lens in contact with plane glass.

Consecutive means if one ring is ‘n’ then other will be (n+1)

λ = 5890x10$^{-8}$ cm, D$_n$ = 2.00 cm, D$_{(n+1)}$= 2.02 cm, R= ?

$ D_{(n+p)}^2 - D_n^2 = \frac{4pλR}{μ} $

For air film μ = 1

$ (2.02)^2 - (2.00)^2 = 4 \times 1 \times 5890 \times 10^{-8} \times R $

Radius of curvature, R = 341 cm