Find the minimum thcknessof a film which will strongly reflect the light of wavelength 589 nm. The refractive index of the material of the film is 1.25.

Answer

`118 mm`

Explanation

For strong reflection, the least optical path difference introduced by the film should be `(lambda)/(2)`.
Using `2 mu t = (lambda)/(2)`
`t = (lambda)/(4 mu) = (589 nm)/(4 xx 1.25) = 118 nm`