Question

What is the thinnest film of a coating with n = 1.39 on glass (n=1.52) for which destructive interference of the red component (650 nm ) of an incident white light beam in air can take place by reflection?

Answer 1

In optics, you have to create a layer of coating that is approximately 1/4 of the light's wavelength. The working equation for this problem is:

d = λ₀/4n, 
where
λ₀ is the wavelength of the incident light
n is the refractive index of the coating

Substituting the values,

d = (650 nm)/4(1.39)
d = 116.9 nm