In Young’s double-slit experiment, a student observed 8 fringes in a certain segment of screen when light of wavelength 600 nm is used. If wavelength is changed to 400 nm, number of fringes in same region will be:
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Question

In Young’s double-slit experiment, a student observed 8 fringes in a certain segment of screen when light of wavelength 600 nm is used. If wavelength is changed to 400 nm, number of fringes in same region will be:

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G1 Physics · Accepted Answer

Step 1: Number of fringes in fixed length L is n ≈ L/β. Step 2: β = λD/d, so n ∝ 1/λ if slit geometry is fixed. Step 3: n₂ = n₁(λ₁/λ₂) = 8(600/400) = 12. Final answer: (D) 12.