1. The problem statement, all variables and given/known data A thin film of alcohol (n=1.36) lies on a flat glass plate (n=1.51). When monochromatic light whose wavelength can be changed, is incident normally, the reflected light is minimum for λ=512 nm and a maximum for λ=640 nm. What is the thickness of the film? 2. Relevant equations λ_n=λ/n 3. The attempt at a solution Let the thickness be t, then we have t/(512/1.36)=m+1/2 where m is an integer. t/(640/1.36)=n where n is an integer. Solving for t and setting the expressions equal, we get 376m+188=471n (using significant figures). I feel like I'm doing something wrong because of the resulting equation. Can someone help me? Thanks.