Question

the far point is $100cm$ for a man. to see the distance object clearly, what is the power of required lens ?

• A. $-1D$
• B. $+1D$
• C. $-3D$
• D. $+3D$

Answer 1

The correct option is A $-1D$

Given,

$v=-100cm$

$u=\infty$

From lens formula,

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

$\frac{1}{f}=\frac{1}{-100}-\frac{1}{\infty }$

$f=-100cm$

Power of the lens,

$P=\frac{1}{f}$

$P=\frac{100}{-100}$

$P=-1D$

The correct option is A.