Question: In a thin film of oil on water, if the thickness of the film is 200 nm and the refractive index of oil is 1.5, what is the wavelength of light in the film?

Options:

1. 400 nm
2. 600 nm
3. 800 nm
4. 1000 nm

Correct Answer: 600 nm

Solution:

Wavelength in the film λ\' = λ/n. If λ = 900 nm, then λ\' = 900 nm / 1.5 = 600 nm.