The radius of curvature of the curved surface of a plano-convex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will ______.

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The radius of curvature of the curved surface of a plano-convex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will act as a convex lens irrespective of the side on which the object lies. Explanation: If object lies on curved side then R1 = +20 cm and R2 = oo, μ1 = 1, μ2 = 1.5 `1/f = (mu_2 - mu_1) (1/R_1 - 1/R_2) 1/f = (1.5 - 1) ($\frac{1}{20}$ - 1/oo) = 0.$\frac{5}{20}$ = $\frac{5}{200}$ = $\frac{1}{40}$` F = + 40 cm If object lies on plane side R1 = oo and R2 = – 20 cm, μ1 = 1, μ2 = 1.5 `1/f = (mu_2 - mu_1) (1/R_1-1/R_2) 1/f = (1.5 - 1)(1/oo - (- $\frac{1}{20}$)) = 0.5 xx (+ $\frac{1}{20}$) 1/f = $\frac{5}{200}$` f = + 40 cm So, lens will always act as a convex lens irrespective of the side on which objects lie. [Solution diagram: 327683_solution_1.png] [Solution diagram: 327683_solution_2.png]

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