What is the minimum thickness of thin film required for constructive interference in the reflected light through it ?
(Given, the refractive index of the film `=1.5,` wavelength of the lilght incident on the film `=600` nm.

Options

A. `100` m,
B. `300` nm
C. `50` nm
D. `200` nm

Answer

A

Explanation

The condition for constructive interference in a thin film of thickness t and refractive index `mu` in the reflected system, for normal incidence is
`2mut=(n+(1)/(2))lambda`
where `n=0,1,2,3`
For minimum thickness, `n=0`
`:. 2mut=(lambda)/(2)`
`t=(lambda)/(4mu)=(600xx10^(-9))/(4xx1.5)=100"nm"`