Assume that the polymer material has a constant refractive index of 1.5. For light of 600nm wavelength at normal incidence, what should the smallest thickness of polymer film be, to reflect minimal light on a perfectly reflective substrate

Minimum thickness will be 100 nm

Explanation:

We have given refractive index is n = 1.5

Wavelength of the light incidence = 600 nm

We have to find the smallest thickness of the film so that there will be minimum light reflect

For minimum thickness of non reflecting film

, here t is thickness, is wavelength and n is refractive index

Putting all values

So minimum thickness will be 100 nm

frequency or wavelenth of em radiation in a vacuum

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.