Question

A man's near point is 0.5 m and far point is 3 m. Power of spectacle lenses required for (i) reading purposes, (ii) seeing distant objects, respectively, are

• A. - 2 D and + 3 D
• B. + 2 D and - 3 D
• C. + 2 D and - 0.33 D
• D. - 2 D and + 0.33 D

Answer 1

Answer: (C)

+ 2 D and - 0.33 D

For reading purposes:

$u=-25cm,v=-50cm,f=?$

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=-\frac{1}{50}+\frac{1}{25}=\frac{1}{50};P=\frac{100}{f}=+2D$

For distant vision, $f^{\prime }=\text{distance of far point}=-3m$

$P=\frac{1}{f^{\prime }}=-\frac{1}{3}D=-0.33D$