The walls of a soap bubble have about the same index of refraction as that of plain water, n=1.33. There is air both inside and outside the bubble. What wavelengths (in air) of visible light are most strongly destroyed from a point on a soap bubble where its wall is 600 nm thick? The visible range is 400nm – 700nm.

Explanation:

The problem is based on the phenomenon of interference in thin films. in this phenomenon , interference of two light beams , one reflected from upper surface and the other ,reflected from lower surface results in formation of colored fringes .  For destruction of light , or for destructive interference the condition is as follows

2μt = n λ where μ is refractive index of light , t is thickness of medium and λ is wavelength of light . n is an integer .

λ  = 2μt / n

= 2 x 1.33 x 600 / n  nm

= 1596/ n nm

if n = 2

λ = 798 nm

if n = 3

λ = 532 nm

n=4

399 nm

out of these wavelengths, only 532 nm falls in the given region of visible light that is 400 nm - 700 nm

So the answer is 532 nm .

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