Question

Distance of eye lens from retina is $2\text{cm}$ for a person. Maximum focal length of the eye lens for the person is $1.96\text{cm}$. Find the far point of the person

• A. $100\text{cm}$
• B. $98\text{cm}$
• C. $102\text{cm}$
• D. $104\text{cm}$

Answer 1

The correct option is B $98\text{cm}$

When the object is kept at far point, its image will be formed on the retina. So, $v=2\text{cm}$

Focal length of the eye-lens, $f=1.96\text{cm}$

Let the far point of the person be $x$.

Using the formula:

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

$\Rightarrow \frac{1}{1.96}=\frac{1}{2}-\frac{1}{-x}$

$\Rightarrow \frac{1}{x}=-\frac{1}{2}+\frac{100}{196}=\frac{-98+100}{196}=\frac{+2}{196}$

$\therefore x=+98\text{cm}$

Hence, $\left(\text{B}\right)$ is the correct answer.

Why this question? Key Concept: The farthest point up to which an eye can clearly see is called far point.