When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane slab of glass. This implies that the liquid must have a refractive index:
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When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane slab of glass. This implies that the liquid must have a refractive index:

G1 Physics · Accepted Answer

Step 1: Lens power in a surrounding medium is P = (μ_lens/μ_medium − 1)(1/R₁ − 1/R₂). Step 2: To behave like a plane slab, the lens must have zero optical power. Step 3: Thus μ_lens/μ_medium − 1 = 0 ⇒ μ_medium = μ_lens = 1.47. Final answer: (A) equal to glass.