Question

A person can see clearly up to a distance of 30 cm He wants to read a book kept at a distance of 40 cm. Find the nature, focal length and power of the lens he requires for his spectacles.

Answer 1

Explanation:

it is a person who is suffering from myopia, therefore he will use concave lenses.

take the object distance (u) = -40cm

& the image distance (v)= -30cm

use 1/v - 1/u = 1/f

by putting the respective value, solve it & u'll get f=-12cm =-0.12m

now, for power p=1/f(in metre)

so, p= -25/3 D = 8.333 D

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