1. The problem statement, all variables and given/known data You are coating a glass lens of index of refraction 1.6 with a film of material of index of refraction 1.7. You start with the thinnest film possible that creates a strong reflection for 610 nm light. You gradually increase the film thickness until you again get strong reflection. What is the thickness of the film now? 2. Relevant equations Not sure where to even start. Any help would be nice! 3. The attempt at a solution Just need to be pointed in the right direction please!