A double convex lens has focal length 25 cm. The radius of curvature of one of the surfaces is double the other. Find the radii, if refractive index of the material of the lens is 1.5.
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A double convex lens has focal length 25 cm. The radius of curvature of one of the surfaces is double the other. Find the radii, if refractive index of the material of the lens is 1.5.

G1 Physics · Accepted Answer

Step 1: Let R₁ = +R, R₂ = −2R, and μ = 1.5. Step 2: 1/f = (μ − 1)(1/R − (−1/(2R))) = (1/2)(3/(2R)) = 3/(4R). Step 3: Set f = 25 cm. Then R = (3/4) × 25 = 18.75 cm and 2R = 37.5 cm. Final answer: (C) 18.75 cm, 37.5 cm.