Question

What is the value of least distance of clear vision.
A) $50$ cm
B) $40$ cm
C) $20$ cm
D) $25$ cm

Answer 1

Hint: Discuss how the image is formed by our eyes. Discuss what clear vision is meant. Then define least distance and state what is its significance.

Complete step by step solution:
As we know that Human eyes are the organ which helps us to see. It works as an organic camera. It allows light and gives us vision. Inside the eyes there are various structures that create images that our brain can understand. Now we will discuss how eyes form images to make us see.
First the light rays fall upon the cornea and get reflected or bent and the light incident on the lens of the eye. As it falls on the lens it bent for a second time and finally the light arrives onto the retina where the image is formed. The image formed in the retina is upside down due to the double reflection. When this is moved to our brain it gains its proper orientation.
Least distance of clear vision means the minimum distance from the object to the eye so that we can visualize it properly.
For the human eye the least distance is $25\;{\text{cm}}$. Generally, it is denoted by $d$ .
It is suggested that if an object is placed at $25\;{\text{cm}}$ from our eye, we will have a clear vision of the object.

So, Here the correct option is option (D).

Note: If we hold an object closer than the least distance, it will form a hazy or blurred image. We must keep in mind that the least distance is not fixed; it changes with ages. Then we must correct it by using proper lenses.