Question

A water film having a refractive index of 1.33 in air is 320 nm thick. If it is illuminated with white light at normal incidence, the light of what wavelength (in nm) will appear to be in reflected light?

Answer 1

For constructive interference from a thin film,

$2\mu d=(n+\frac{1}{2})\lambda$

$⟹$For $n=1$, $\lambda =570nm$