Question

In Newton’s ring experiment, the diameter of the 10^th ring changes from 1.40 to 1.23 cm when a liquid is introduced between the lens and glass plate. What is the refractive index of the liquid?

(a) 1.05

(b) 1.15

(c) 1.25

(d) 1.35

Answer 1

Correct choice is (c) 1.25

The best I can explain: We know, Dn^2 = 4nλR/μ

Without liquid in air, μ = 1, D10^2 = 40λR

With liquid, D10^2’ = 40λR/μ

Dividing both we get, μ = D10^2 D10^2’

= {1.40/1.27}^2

= 1.25.