Question

Question about thin film interference: A soap film is illuminated by white light normal to it's surface. The index of refraction of the film is 1.5. Wavelenghts of 480nm and 800nm, and no other wavelenghts between them are intensified because of constructive interference in the relected beam. What is the thickness of the beam?

Answer 1

Sorry, "What is the thickness of the film?"

Answer 2

Optical path travelled is 2ne where n is the index and e is the thickness.

This optical path must be a multiple of both wavelengths with no other wavelength in between.

Answer 3

yea but the path difference is 2ne - lambda/2 cause when waves encounter reflection off a denser medium they undergo a phase change which corresponds to a path difference of lambda/2

Answer 4

@Mashy. Correct, I was thinking about anti-reflection coating in which both rays undergo change of phase.