Question

A thin film of a substance with a refractive index of 1.20 floats on a water surface with a refractive index 1.30.
2.1. White light (wavelength 400 - 700 nm) that strikes this film from the air in an area where the thickness of
Thin film is 460 nm. Which wavelength of light will reflect the most?
2.2. If in the water area under this thin film What wavelength of light is going to penetrate the most?

Thank you so much

Answer 1

Explanation:

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Answer 2

Answer:

Part of the light reflected from the bottom surface can emerge from the top of the film (ray 2) and interfere with light reflected from the top (ray 1). Since the ray that enters the film travels a greater distance, it may be in or out of phase with the ray reflected from the top. However, consider for a moment, again, the bubbles in Figure 1. The bubbles are darkest where they are thinnest. Furthermore, if you observe a soap bubble carefully, you will note it gets dark at the point where it breaks. For very thin films, the difference in path lengths of ray 1 and ray 2 in Figure 2 is negligible; so why should they interfere destructively and not constructively? The answer is that a phase change can occur upon reflection. The rule is as follows:

When light reflects from a medium having an index of refraction greater than that of the medium in which it is traveling, a 180º phase change (or a λ / 2 shift) occurs.