Question

The near point of a myopic eye is $15$ cm. What should be the power of the lens which will enable the eye to read a book placed at $30$ cm?

• A. $3.33$ dioptre
• B. $-3.33$ dioptre
• C. $2.22$ dioptre
• D. $-2.22$ dioptre

Answer 1

Answer: (B)

$-3.33$ dioptre

Given:- v=-15cm

u=-30cm

from lens formula.

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}=\frac{1}{-15}+\frac{1}{30}=\frac{1}{f}$

$\frac{1}{f}=\frac{-1}{30}{cm}^{-1}$ .

So power of lens = $\frac{1}{f}=\frac{-1}{0.3}{m}^{-1}$

P= -3.33D.