Question

The focal length of a normal and relaxed eye lens is about -

• A. $1\text{mm}$
• B. $2\text{cm}$
• C. $2\text{mm}$
• D. $1\text{cm}$

Answer 1

The correct option is B $2\text{cm}$

The focal length of a normal and relaxed eye lens is about $2\text{cm}$ because a normal eye has retina, $2\text{cm}$ behind the eye lens and the image of object at infinity (relaxed view) is formed at retina.

So, the focal length of a normal eye lens is equal to the distance between the eye lens and retina, $i.e.$ about $2\text{cm}$.

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