## Physics: Principles with Applications (7th Edition)

If the film’s index of refraction is lower/higher than that of the material on both sides of itself, a $180^{\circ}$ phase shift will occur at one interface but not at the other. However, if the film has a lower-index material on one side and a higher-index material on the other, then phase shifts occur at neither interface, or at both interfaces. None of the statements A-D will always hold; It depends on how the film's index of refraction compared to those of its neighbors.