Optics Question 875

Question: A certain region of a soap bubble reflects red light of wavelength λ=650nm . What is the minimum thickness that this region of the soap bubble could have? Take the index of reflection of the soap film to be 1.41.

Options:

A) 1.2×107m

B) 650×109m

C) 120×107m

D) 650×105m

Show Answer

Answer:

Correct Answer: A

Solution:

[a] There is air on both sides of the soap film.

the reflections of the light produce a net 180 phase shift.

The condition for bright fringes is 2t=(m+1/2)λfilm

t=(m+1/2)λfilm2=(m+1/2)λ2n

=(1/2)(650×109m)2(1.41)=1.2×107m



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