A parallel beam of light of wavelength 560 nm falls on a thin film of oil (refractive index = 1.4). What shoul be the minimum thickness of the film so that it strongly reflects the light?
Given that, λ=560×10−9m,μ=1.4
For strong reflection,
2μd=(2n+1)λ2⇒μ=(2n+1)(λ)4d⇒d=(2n+1)14μ
For minimum thickness, putting n = 0
⇒d=λ4d⇒d=560×10−614=10−7m=100nm