Question

You are standing in air and are looking at a flat piece of glass (n = 1.52) on which there is a layer of transparent plastic (n = 1.61). Light whose wavelength is 622 nm in vacuum is incident nearly perpendicularly on the coated glass and reflects into your eyes. The layer of plastic looks dark. Find the smallest possible nonzero value for the thickness of the layer.

Answer 1

step:1

Given that

refractive index of glass =1.52

refractive index of plastic =1.61

wavelength =622*10^-9 m

step:2

now we find the refractive index

refractive index =/=1.61/1.52=1.1

step:3

now we find the thickness

thickness t=wavelength/(-1)

                 =622*10^-9/(1.1-1)

                  =6.22*10^-6 m