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Physics · PYQ NEET UG 2019(2)
हिन्दीA double convex lens has focal length \( 25\text{ cm} \). The radius of curvature of one of the surfaces is double of the other. Find the radii if the refractive index of the material of the lens is \( 1.5 \).
Correct answer · Option 4
\( 18.75\text{ cm}, 37.5\text{ cm} \)
Explanation
Using lens maker's formula: \( \frac{1}{f} = (\mu - 1)(\frac{1}{R_1} - \frac{1}{R_2}) \). Let \( R_1 = R \) and \( R_2 = -2R \). \( \frac{1}{25} = (1.5 - 1)(\frac{1}{R} - \frac{1}{-2R}) = 0.5 \times \frac{3}{2R} = \frac{3}{4R} \implies R = \frac{75}{4} = 18.75\text{ cm} \). Thus radii are \( 18.75\text{ cm} \) and \( 37.5\text{ cm} \).
