In a classroom demonstration of thin films, your physics teacher takes a glass p

Question

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. The indices of refraction of air, the oil, and the glass are 1.0, 1.4, and 1.5, respectively. Standing near the light source, you observe that the film appears green. This corresponds to a wavelength of 520 nm.

find the wavelength of the light in the oil film, the frequency of the light in the oil film, and the frequency of the light in the air

calculate the minimum thickness of the oil film other than zero such that the observed green light is the most intense.

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.

thank you so much

Explanation / Answer

The wavelength of light = 520 nm The refractive index of the oil n = 1.4 (a) The wavelength of the light in oil film        The refractive index n = air / oil Then wavelength oil = air/n = 520 nm/1.4                                                  = 371.4 nm The frequency of light in air is      v = f then frequency f = v/ = (3*10^8 m/s)/(520*10^-9 m)                                     = 5.76*10^14 Hz The frequency should not change from one medium to another so the frequency is same in all media. when the light reflects off the surface of the oil and glass and  if the light happens to travel exactly one wavelength farther through the oil and reflect back, it will create constructive interference. then 2t = n therefore thickness t = /2                                   = (371.4 *10^-9 m) / 2                                    = 185.7 *10^-9 = 185 nm

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