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A soap bubble (n = 1.33) is floating in ...

A soap bubble `(n = 1.33)` is floating in air. If the thickness of the bubble wall is 115 nm, what is the wavelength of the light that is most strongly reflected?

Text Solution

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Light reflecting from the first suffer phase reversal. Light reflecting from the second surface does not, but passes twice through the thickness t of the film. So for consturctive interference, we require
`(lambda_(n))/(2) + 2 t = lambda n`
where `lambda_(n) = (lambda)/(n)` is the wavelength in the material.
Then, `2 t = (lambda_(n))/(2) = (lambda)/(2n)`
`:. lambda = 4 nt = 4 (1.33) (115nm) = 612 nm`
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