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Question

A double convex lens is made of glass of refractive index 1.5. If its focal length is 30cm, then radius of curvature of each of its curved surface is

A
30cm
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B
15cm
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C
18cm
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D
None of these
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Solution

The correct option is B 30cmGiven, a double convex lens is made of glass where refractive index,μ=1.5 and focal length, f=30cm.As it is double convex lens, let, R1=+R and R2=−R.Now, according to lens maker's formula, 1F=(μ−1)(1R1−1R2)Using the given values, we have, 130=(1.5−1)(1R−1−R)Or, 130=0.5(2R)=1RTherefore, radius of curvature of each of its curved surface is, R=30cmSo, correct option is - (A) 30cm

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