Question

Minimum and maximum distance should be for clear vision of healthy human eye is:
A. 100cm and 500cm
B. Infinite and 25cm
C. 25cm and 100cm
D. 25cm and infinite

Answer 1

Hint: Human eye has a special type of lens which is convex in nature. This is called eye lens. The special feature of this lens is that it can adjust its focal length as per the location of the object. After focusing onto an object, it creates an image on the retina of our eye to get the maximum intensity of the object’s image. But this lens has to get contracted to focus on nearby objects. This contraction has a limit called limit of human vision or near point of human eye.

Complete answer:
By the term infinite, what could be understood? Well it's something very far or very large. But what about the length of Titanic in comparison to the needle? It's also very large.

In optics, usually the object is considered to be at infinity if the distance of the object from the lens is much greater than the size of lens or we can say if the rays coming towards the lens are almost parallel, we can say that the object is at infinity.

As we can see the sun, moon and the stars, it means that the far point (or the maximum human limit) of the human eye is infinity.

Coming to a near point, notice that whenever we look at something from very close distance, after some point we begin to feel strain on the eye. That point is called the near point and it is 25cm for the human eye.

So, the correct answer is “Option D”.

Note:
One might get confused that if the human eye can see up to any distance possible, then why aren't we able to see Pluto or distant planets or galaxies? This is because we’re able to see only that object from which light comes directly or indirectly in our eye. The light coming from these planets is so less intense that we need special apparatus to see them.