Question: In a thin film of soap, if the refractive index is 1.33 and the wavelength of light in air is 500 nm, what is the effective wavelength in the film?

Options:

1. 375 nm
2. 500 nm
3. 600 nm
4. 750 nm

Correct Answer: 375 nm

Solution:

Effective wavelength in the film = λ/n = 500 nm / 1.33 ≈ 375 nm.