Working of an Eye


 
 
Concept Explanation
 

Working of an Eye

Working Of Eye or Light Control:: Light rays after reflecting from the object enter the eye first through the cornea, which is a clear dome in the front of the eye.The light then progresses through the pupil and than passes through the crystalline lens, which is located immediately behind the iris and pupil.The iris controls the diameter of the pupil automatically. Initially, the light waves are bent or converged first by the cornea , and then by the crystalline lens. In dim light, the iris widens (or dilates) the pupil to admit more light into the eye. In bright light, it contracts the pupil so that less light goes in. With in the layer of the retina, light impulses are changed into electrical signals, then sent to the brain through the optic nerves.  In this way, the iris-pupil combination controls the amount of light into the eye to ensure that the best-possible image is formed under different light conditions.

Between the cornea and the lens lies a muscular diaphragm called the iris. The round, coloured part that we see in the eye is the iris.Iris gives distinct colour to the eye. When we say that the person has green eyes, we actually refer to the colour of the iris. It has a small opening called the pupil, through which light enters the eye. The iris controls the diameter of the pupil automatically. In dim light, the iris widens (or dilates) the pupil to admit more light into the eye. In bright light, it contracts the pupil so that less light goes in. In this way, the iris-pupil combination controls the amount of light into the eye to ensure that the best-possible image is formed under different light conditions.

Persistance Of Vision:  The image of the object formed on the retina of the eye does not disappear immediately. Even if the object is removed, the image of any object seen will last for one sixteenth of a second on the retina. This eye sensation that lasts for a period of time is called visual persistence. So, if still images of a moving object are flashed on the eye at a rate faster than 16 per second, then the eye perceives that object is moving. That's why a series of fast-moving still pictures can create an illusion of movement. This property of  of vision is used in cinematography.

 

Sample Questions
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Question : 1

A human eye employs a ______________ lens to form ___________ images.

Right Option : A
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Question : 2

Refractive power of cornea in human beings is approximately _______________.

Right Option : C
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Question : 3

The persistence of an eye vision is for _____________.

Right Option : D
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Explanation
 
 


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