A soap film (index of refraction nf=1.33) is suspended in air. White light is incident from air onto the film at normal incidence.
(a) Identify and justify the phase change at each of the first two reflections.
(b) Explain the destructive-interference condition for a quarter-wavelength film at normal incidence.
(c) Describe qualitatively why the dominant reflected wavelength becomes shorter when the viewing angle is increased.