Q24 of 27 Page 132

Find the radii of curvature of a convexo- concave convergent lens made of glass with refractive index n-1.5 having focal length of 24cm. One of the radii of curvature is double the other.

Using formula: Lens Maker’s Formula:


f = focal length


R1 = radius of curvature of the lens surface closer to the source of light


R2 = radius of curvature of the lens surface farther to the source of light


n = Refractive index


Given: focal length (f) = 24 cm


One of the radii of curvature is double the other that is if R1 = R then R2 = 2R


n = Refractive index = 1.5


For convexo-concave lens both the radii are positive.






2R = 0.5 × 24


R = 12/2 = 6cm


R1 = R = 6 cm


R2 = 2R = 12 cm


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