Question

In the diagram shown, the separation between the slit is equal to 3λ, where λ is the wavelength of the light incident on the plane of the slits. A thin film of thickness 3λ and refractive index 2 has been placed in the front of the upper slit. The distance of the central maxima on the screen from O is ______.

 

Options

• D

• `(lambdad)/D`

• `(lambdaD)/d`

• None of these

Answer 1

In the diagram shown, the separation between the slit is equal to 3λ, where λ is the wavelength of the light incident on the plane of the slits. A thin film of thickness 3λ and refractive index 2 has been placed in the front of the upper slit. The distance of the central maxima on the screen from O is D.

Explanation:

The separation between the slit d = 3λ

So, fringe width = `beta = (lambdaD)/d = (lambdaD)/(3lambda) = D/3`

When A thin film with a thickness of 3λ and a refractive index of 2 is placed in front of the upper slit, the distance between the central maxima on the screen and O is

`x = beta/lambda(mu - 1)t`

here `beta = D/3, t = 3lambda` and μ = 2

So, distance `x = D/(3lambda)(2 - 1) xx 3lambda`

x = D