Q5 of 27 Page 132

Write the lens maker's formula and explain the terms in it. (AS1)

A lens forms an image of an object after the light rays coming from the object gets refracted by the two bounding surface of the lens.

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 of the lens material with respect to the surrounding medium


This formula is used to determine the values of R1 & R2 needed for a desired focal length of a lens of a given refractive index. The values of both the radii should be taken with their signs. For thin lens, focal length is independent of the order of surface.


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