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 ___ cm.

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Solution

Use this formula,
$f = \frac{R}{2 (μ - 1)} \Rightarrow f = \frac{40}{2 (1.65 - 1)} = 30.7 c m \approx 31 c m$

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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 ___ cm.

Use this formula, f=R2(μ−1)⇒f=402(1.65−1)=30.7cm≈31cm

Use this formula,
$f = \frac{R}{2 (μ - 1)} \Rightarrow f = \frac{40}{2 (1.65 - 1)} = 30.7 c m \approx 31 c m$