What is the thinnest soap film (excluding the case of zero thickness) that appea

Question

What is the thinnest soap film (excluding the case of zero thickness) that appears black when illuminated with light with a wavelength of 455 nm ? The index of refraction of the film is 1.35, and there is air on both sides of the film.

Express your answer in nanometers.

Part A What is the thinnest soap film (excluding the case of zero thickness) that appears black when illuminated with light with a wavelength of 455 nm? The index of refraction of the film is 1.35, and there is air on both sides of the film. Express your answer in nanometers View Available Hint(s) 307.13 nm Submit Previous Answers X Incorrect; One attempt remaining: Try Again Provide Feedback

Explanation / Answer

For dark (destructive interference) 2 t = lambda or 2 lambda or 3 lambda etc so thinnest is when 2 t = 455 nm/1.35 (you ned to use lambda in the film)
so t = 455 nm /2.7 = 168.52 nm
You use multiples of lambda for a dark spot because there is a phase change at one reflection (air to film) and no phase change at the other (film to air)

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