Question

Calculate the focal length of a lens needed by a woman whose near point is 50cm from her eyes, assuming the least distance of distinct vision for a normal eye is 25cm. ​

Answer 1

The focal length of a lens needed by a woman whose near point is 50cm from her eyes is 50cm.

To find the answer, we have to know about the focal length of correcting lens.

How to find the focal length of correcting lens?

• If x is the distance of nearest point of the defective eye and D is the least distance of distinct vision, then, the expression for focal length of the correcting lens will be,

                           $f=\frac{XD}{X-D}$

• It is given that, the woman whose near point is 50cm from her eyes, assuming the least distance of distinct vision for a normal eye is 25cm. Thus, the focal length will be,

                       $f=\frac{50*25}{50-25} =50cm.$

Thus, we can conclude that, the focal length of a lens needed by a woman whose near point is 50cm from her eyes is 50cm.

Learn more about the focal length here:

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