Apiece of glass has a thin film of gasoline floating on it. a beam of light is shining perpendicular on the film. if the wavelength of light incident on the film is 560 nm and the indices of refraction of gasoline and glass are 1.40 and 1.50, respectively, what is the minimum nonzero thickness of the film to see a bright reflection?

200 nm

Explanation:

We need a constructive interference to see the bright reflection

we know that  where m=1 and is the wavelength of the gasoline

so

putting the value of m and in thickness equation

so the thickness of the film will be 200 nm

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