1. The problem statement, all variables and given/known data I don't have a question on a specific problem, I am more caught up in the determination of the phases- I'll give a general problem to use as an example: In Fig. 35-41, light is incident perpendicularly on a thin layer of material 2 that lies between (thicker) materials 1 and 3. The waves of rays r1 and r2 interfere, and here we consider the type of interference to be either maximum (max) or minimum (min). We are given: n1=1.32 n2=1.75 n3=1.39 we want to find a max for the 3rd least thickness of L (in nm) λ=382nm (in air) Figure: rays are tilted for clarity 2. Relevant equations Since we want a maximum, the general equation for a maximum would be: 2L=(m+1/2)λ/n2 3. The attempt at a solution in the case of this problem, we add an additional λ/2 for the incidence of r1 on n2. so my real question is this- why is it that you multiply m by 2 to end up with 2m+1 in this case? when do you just use (m+1)λ vs (2m+1/2)λ I've been reading and researching for hours now, so any help would truly be appreciated.