Question

A myopic person can not see objects lying beyond $2m$. The focal length and power of the lens required to remove this defect will be

• A. $1$ m and $0.5$ D
• B. $-2$ m and $-0.5$ D
• C. $0.5$ m and $0.5$ D
• D. $-0.5$ m and $0.5$ D

Answer 1

The correct option is B $-2$ m and $-0.5$ D

$u=+2m$
$v=\infty$
use lens formula
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
where u = distance of object
$v=$ distance of image
$f=$focal length
$P=$power
put the values
$\frac{1}{\infty }-\frac{1}{2}=\frac{1}{f}$
$f=-2m$
$P=\frac{1}{f}=\frac{1}{2}=0.5D$