For this problem, you will only be concerned with the geometric aspects of thin-film interference, so ignore phase shifts caused by reflection from a medium with higher index of refraction. (Because of the structure of a butterfly's wings, such phase shifts do not contribute much to what you actually see when you look at the butterfly.) Part A Assume that light is incident normal to the surface of a film of thickness d. How much farther does the light reflected from the back surface travel than the light reflected from the front surface