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The smallest size of a cell which can be seen with unaided eye is or differentiation capacity of human eye is
(a) 1 micron
(b) 10 micron
(c) 100 micron
(d) 1000 micron

Answer
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Hint: The unaided human eye can see down to slightly less than 100μm. Everyone can see the diameter of a human hair, which is approximately 100μm (0.1mm).
It depends on the convex lens present in the eye and its resolving powers.

Complete answer:A naked eye can see objects of any size, if they emit or scatter enough light to trigger its detector cells.
What is limited now, is the eye’s resolution i.e. how close two objects can appear before they blur into one. It allows light perception, color vision and depth perception. There are many parts of a human eye. The different parts of the eye have different refractive indexes, and this is what bends the rays to form a proper interpretable image.

The cornea provides two-thirds of the power to the eye and the lens further provides the remaining power. The image passes through several layers of the eye, but this happens in a way very similar to that of a convex lens.
When the image ultimately reaches the retina, it is inverted, but the brain is well equipped to depict it in the form that we perceive objects. In order for the vision to be clear, the image has to be formed directly on the retina.
The focus needs to be altered, much like a camera, depending on the distance and size of the object. The eye’s lens is flexible, and keeps changing its shape. This changes the focal length. The eye’s ciliary muscles control the shape of the lens.

When we focus on something, it is possible due to the ciliary muscles by either squeezing or relaxing them. Generally, the size range of cells like egg cells, unusually large bacteria, some amoebas and squid nerve cells are of the range of 100 microns and these are visible to the naked eye.

So, the correct answer is ‘100 micron’.

Note:Resolving power of the human eye lens is the ability of the lens to differentiate an object as a separate image.
The human eye has a convex lens and the visibility of the eye depends solely on its resolving power.