1. The problem statement, all variables and given/known data Would you see the same thin film interference pattern in a film of soap surrounded by air and a film of soap on glass? Why or why not? 2. Relevant equations None 3. The attempt at a solution Yes, you would see the same thin film interference pattern in a film of soap surrounded by air and a film of soap on glass. In thin films of soap and oil, visible colour bands are the result of interference of light. In this situation, the interference is caused by the interference of light waves reflected from the opposite surfaces of thin films, therefore, the phase change is negligible to the pattern produced. Here are two images from my textbook (Nelson Physics 12) that show the scenario. They appear to be almost the same, except for the phase change to glass in the first image. Does the phase change affect the interference pattern that the viewers see? Or are rays 1-3 the only ones of importance in the pattern? Any clarification is much appreciated!