A thin double convex lens has radii of curvature each of magnitude 40 cm and is made of glass with refractive index 1.65. Its focal length is nearly

20 cm

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31 cm

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35 cm

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50 cm

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Solution

The correct option is B 31 cm
By using $f = \frac{R}{2 (μ - 1)} \Rightarrow f = \frac{40}{2 (1.65 - 1)} = 30.7 c m \approx 31 c m$ .

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A thin double convex lens has radii of curvature each of magnitude 40 cm and is made of glass with refractive index 1.65. Its focal length is nearly

The correct option is B 31 cmBy using f=R2(μ−1)⇒f=402(1.65−1)=30.7cm≈31cm.

The correct option is B 31 cm
By using $f = \frac{R}{2 (μ - 1)} \Rightarrow f = \frac{40}{2 (1.65 - 1)} = 30.7 c m \approx 31 c m$ .