Question:
White light reflected at normal incidence from a soap film has minima at 6500 Å and maxima at 7500 Å in the visible region with no minimum in between. If $μ$ is 5/3 for the film, the thickness of film is:
White light reflected at normal incidence from a soap film has minima at 6500 Å and maxima at 7500 Å in the visible region with no minimum in between. If $μ$ is 5/3 for the film, the thickness of film is:
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For thin film interference, condition depends on phase change at reflection.
Updated On: Apr 16, 2026
- $7.40 × 10^-7$ cm
- $9.75 × 10^-5$ mm
- $9.70 × 10^-7$ cm
- $9.75 × 10^-4$ mm
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The Correct Option is B
Solution and Explanation
Step 1: For reflected light, minima: $2μ t = n\lambda₁$, maxima: $2μ t = (m+\frac12)\lambda₂$.
Step 2: Solving gives $t = 9.75 × 10^-5$ mm.
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