Question

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

• A. $1\text{m}\&0.5\text{D}$
• B. $-2\text{m}\&-0.5\text{D}$
• C. $0.5\text{m}\&0.5\text{D}$
• D. $-0.5\text{m}\&0.5\text{D}$

Answer 1

The correct option is B $-2\text{m}\&-0.5\text{D}$

In this case,
$v=-2\text{m}$
$u=-\infty$
Apply lens formula
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\frac{1}{-2}-\frac{1}{-\infty }=\frac{1}{f}$
$f=-2\text{m}$
Power of corrective lens is
$P=\frac{1}{f}=\frac{1}{-2}=-0.5\text{D}$