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JEE Main 2025 (29 Jan, Shift 2) · Combination of Lenses

Combination of Lenses question from JEE Main 2025 (29 Jan, Shift 2)

Q18JEE Main 2025 · 29 JAN · SHIFT 2Medium

Combination of Lenses

Two identical symmetric double convex lenses of focal length f are cut into two equal parts L1, L2 by AB plane and L3, L4 by XY plane as shown in figure respectively. The ratio of focal lengths of lenses L1 and L3 is

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Answer: (a)

Cut by AB (along the axis): L1 keeps both curved surfaces, so $f_1 = f$ .
Cut by XY (plane of the lens): L3 is plano-convex, so $f_3 = 2f$ .
So the answer is (a) $f_1 : f_3 = 1 : 2$ .

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