. A concave convex lens has an index of refraction 1.5 and the radii of curvature of its surfaces are 10 cm and 20 cm. The concave surface is upwards and it is filled with oil μ = 1.6 . Find the focal

Question

. A concave convex lens has an index of refraction 1.5 and the radii of curvature of its surfaces are 10 cm and 20 cm. The concave surface is upwards and it is filled with oil μ = 1.6 . Find the focal length of oil glass combination.

TestHub · Accepted Answer

Glass concavo-convex lens: f g ​ 1 ​ = ( 1.5 − 1 ) ( 10 1 ​ − 20 1 ​ ) = 40 1 ​ ⇒ f g ​ = 40 cm . The oil (μ = 1.6) resting in the concave surface (R = 20 cm) forms a plano-convex lens: f o ​ = 1.6 − 1 20 ​ = 33.33 cm . In contact: F 1 ​ = 40 1 ​ + 33.33 1 ​ = 0.055 ⇒ F = 18.18 cm . Hence (A).

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