A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will:
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Question

A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will:

G1 Physics · Accepted Answer

Step 1: Relative refractive index μ_rel = μ_lens/μ_liquid = 1. Step 2: Lens-maker formula gives 1/f = (μ_rel − 1)(1/R₁ − 1/R₂) = 0. Step 3: Optical power is zero, so the focal length becomes infinite. Final answer: (B).