Question

When the liquid is introduced between the lens and plate, the diameter of the rings


increase

decrease

none of thes

remain same​

Answer 1

It will decrease

● Since diameter of the ring is inversely proportional to the square root of refractive index of the medium between the planoconvex lens and plane glass plate, therefore as refractive index increases, diameter of the rings decrease, that is the rings contract.

Answer 2

Newton's Ring Test

decrease

Newton's ring test is used to calculate the efficiency of Plano convex lens. Rings are formed when reflection and refraction of light takes place and reflected and refracted rays superimposed and results into formation of ring.

The experiment set up for Newton's ring is attached in image.

For nth bright fringe,

$D_n=\sqrt{4(n-\frac{1}{2})\frac{\lambda R}{\mu} }$

For nth dark fringe,

$D_n=\sqrt{2(n\frac{\lambda R}{\mu}) }$

where $D_n$ is diameter of ring

R is refractive index

We can see that diameter of newton's ring is inversely proportional to refractive index. So when liquid is introduced refractive index will increase so diameter will decrease.