Answer to Question #92938 in Optics for Ishika Bansal

Question

Two plano convex lens each of radius 100 are placed with their curved surfaces in contact with each other. Newton's rings are formed by a light of wavelength 6000A°. Find the distance between 10th and 20th fringe.

Answer 1

We can write for the radius of dark ring

$r_{k}=\sqrt{kRλ} (1)$

In our two cases

$r_{10}=\sqrt{10Rλ} (2)$

$r_{20}=\sqrt{20Rλ} (3)$

The distance between 10th and 20th fringe is equal to

$Δr=\sqrt{20Rλ}-\sqrt{10Rλ} (4)$

Using (4) we get

Δr=8.83×10^-3 m

Answer

8.83×10^-3 m