Question

A person is able to clearly see an object placed at $60\text{cm}$ from his eye. The focal length of the eye lens in this scenario is $2\text{cm}$. What is the distance of the eye-lens from the retina?

• A. $2.06\text{cm}$
• B. $2.20\text{cm}$
• C. $1.97\text{cm}$
• D. $2.35\text{cm}$

Answer 1

The correct option is A $2.06\text{cm}$

Given:
Focal length of eye-lens, $f=2\text{cm}$
Object distance, $u=-60\text{cm}$

Let the distance of eye-lens from retina is $x$. Since the person is clearly able to see the object, the image is formed on the retina.
$\therefore$ image distance is, $v=x$

Using lens formula,
$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

$\frac{1}{2}=\frac{1}{x}+\frac{1}{60}$

$\Rightarrow \frac{1}{x}=\frac{1}{2}-\frac{1}{60}=\frac{29}{60}$

$\therefore x=\frac{60}{29}=2.07\text{cm}$

Hence, $\left(A\right)$ is the correct answer.