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QJEEM20Ph058f: JEE Main 2020 Physics - Class 12 JEEM20Ph058f Solution: A point object in air is in front of the curved surface of a…

A point object in air is in front of the curved surface of a plano-convex lens. The radius of curvature of the curved surface is 30 cm and the refractive index of the lens material is 1.5, then the focal length of the lens (in cm) is ______.

Step-by-Step Verified Solution

Lens-maker formula

1f=(μ−1)(1R1−1R2){1 \over f} = \left( {\mu - 1} \right)\left( {{1 \over {{R_1}}} - {1 \over {{R_2}}}} \right)

for plano-convex lens

R1{{R_1}} = ∞\infty and R2 = -R

∴\therefore f = Rμ−1{R \over {\mu - 1}} = 301.5−1{{30} \over {1.5 - 1}} = 60 cm

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