Lens Makers Formula

Introduction

In optics, lenses are generally used for the convergence of light and the formation of images. The formula guiding us to determine the focal length of the lens, which is of great importance in optical devices like eyeglasses, microscopes, cameras, and many more, is known as the Lens Maker's Formula.

Formula Of Lens Makers

The formula for the maker of lenses is an equation used in the computation of the focal length of a lens from its physical characteristics and the refractive properties of the lens material. It gives the connection between the focal length of the lens, its radii of curvature, and the refractive index of the material from which it is made.

The Formula of Lens Maker is given by :

 

Where,

f = Len focal length

μ = Refractive index of the material

the radius of curvature of both surfaces

Solved Problem

Example: Find the focal length of the lens whose refractive index is given 2 and the radius of curvature of two surfaces respectively 20cm and -35cm.

Solution:

Given

    μ = 2

    R1=30cm

    R2 =-45cm

 Lens formula:

= 1 (1/30 + 1/45)

= 0.03 + 0.022

= 0.052

Thus, f = 1 / 0.052

f = 19.23 cm

 

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