## Supplemental Problem.
In a classroom demonstration of thin films, your physics teacher takes a glass plate and places a thin layer of transparent oil on top of it. The oil film is then illuminated by shining a narrow beam of white light perpendicularly onto the oil's surface, as shown above. The indices of refraction of air, the oil, and the glass plate are given in the diagram. Standing near the light source, you observe that the film appears green. This corresponds to a wavelength of 520 nm .
(a) Determine each of the following for the green light.
i. The frequency of the light in air
ii. The frequency of the light in the oil film
iii. The wavelength of the light in the oil film
(b) Calculate the minimum thickness of the oil film (other than zero) such that the observed green light is the most intense.
(c) As your teacher changes the angle of the light source, the light you observe from the film changes color. Give an explanation for this phenomenon.