Young’s double-slit experiment is first performed in air and then in a medium other than air. Fifth dark fringe in air is equal to eighth bright fringe in the medium. Refractive index of medium is nearly:
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Question

Young’s double-slit experiment is first performed in air and then in a medium other than air. Fifth dark fringe in air is equal to eighth bright fringe in the medium. Refractive index of medium is nearly:

Options

G1 Physics · Accepted Answer

Step 1: Fifth dark fringe in air: x = (2×5−1)λ_air D/(2d) = 9λ_air D/(2d). Step 2: Eighth bright fringe in medium: x = 8λ_medium D/d. Step 3: Equate 9λ_air/2 = 8λ_medium ⇒ λ_air/λ_medium = 16/9 ≈ 1.78. Final answer: (D) 1.78.