A soap bubble consists of a thin film of soapy water (index of refraction n=1.34) surrounded by air on both sides. At one region of the bubble, the film thickness is approximately 250nm. White light is incident normally on this region.
Answer the following questions qualitatively; numerical calculation of exact wavelengths is not required.
(a) Describe what happens to the phase of the light waves reflected from the top and bottom surfaces of the film, and explain why the two reflected waves can interfere.
(b) Taking into account both the optical path difference and the phase changes you identified in part (a), explain which portions of the visible spectrum (short, middle, or long wavelengths) will be brightest in the reflected light from this region.
(c) Using your reasoning from parts (a) and (b), state whether light with wavelength 550nm in air will appear relatively bright or relatively dim in the reflected light, and justify your answer without performing a detailed numerical calculation.