A person wants to read a book placed at 20 cm whereas the near poit of his eyes is 50 cm. Calculate the power of the lens required.

Explanation

Given y = -20 cm, v = -50 cm, P = ?
Using lens formula,
`f = (u v)/(v-u) = ((-20) xx (-50))/(-50 + 20) = -33.33 cm`
`:. P = (100)/(f) = (100)/(-33.33) = -3D`