What is the minimum thickness of a soap bubble required for constructive interference in reflected light of wavelength 900 nm? The refractive index of the film is μ=1.5.
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Question

What is the minimum thickness of a soap bubble required for constructive interference in reflected light of wavelength 900 nm? The refractive index of the film is μ=1.5.

G1 Physics · Accepted Answer

For the thinnest soap film producing constructive reflected interference, one phase reversal occurs. Thus 2μt=λ/2. Hence t=λ/(4μ)=900 nm/(4×1.5)=150 nm. Option B.