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JEE Main 2026 Physics question

PhysicsRay Optics and Optical InstrumentsJEE Main 2026

If sunlight is focused on a paper using convex lens, it starts burning the paper in shortest time when the lens is kept at 30 cm above the paper. If the radius of curvature of the lens is 60 cm then the refractive index of the lens material is . The value of α is .

Answer: 20

Solution

The paper burns fastest at the focus, so f = 30 cm. For an equiconvex lens

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Question ID VK-015158