In a thin film of thickness t with refractive index n, condition for destructive interference for reflected light (no phase change on reflection conditions):
A2nt = nλ
B2nt = (m + 1/2)λ
C2nt = mλ
Dnt = mλ
Answer & Solution
Correct answer: C. 2nt = mλ
For a thin film with one phase change of pi at reflection from denser medium, destructive interference: 2nt = mλ for m = 0, 1, 2, ... This is why soap bubbles show coloured patterns.
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