A lens is made of glass having an index of refraction 1 . 5 . One side of the lens is flat and the other side is convex with a radius R . If an object is placed 60 cm , towards the convex side of the lens, the image is formed at 120 cm on the other side of the lens. The value of R is

Question

A lens is made of glass having an index of refraction 1 . 5 . One side of the lens is flat and the other side is convex with a radius R . If an object is placed 60 cm , towards the convex side of the lens, the image is formed at 120 cm on the other side of the lens. The value of R is ​​​​​​​, 20 cm, 40 3 cm, 33 cm, 18 cm

MARKS App · Accepted Answer

Using lens maker's formula, 1 f = μ 2 μ 1 - 1 1 R 1 - 1 R 2 ⇒ 1 f = 1 2 1 R ⇒ f = 2 R Now using lens equation, 1 v - 1 u = 1 f ⇒ 1 120 - 1 - 60 = 1 2 R ⇒ 2 R = 40 cm ⇒ R = 20 cm

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