# Double-convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature.

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Double-convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20 cm?

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Given: n = 1.55, f = 20 cm,

R1 = R and R2 = – R

(By sign convention)

To Find: Radius of curvature (R)

Calculation: From formula,

∴ R = $\frac{1.10}{1}$ × 20 = 22 cm