What is the minimum thickness of a thin film required for constructive interference in the reflected light from it ?
Give, the refractive index of the film = `1.5` wavelength of the light incident on the film = 600 nm

Options

A. 100 nm
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))lamda`
where `n=0,1,2,3,`
For minimum thickness, `n=0`
`t=(lamda)/(4mu)=(600xx10^(-9))/(4xx1.5)=100nm`