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 throught he 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 cortex region of 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. 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 sisteenth of a second on the retina. This eye sensation that lasts for a period of time is called visual persistence. 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

The presistence of the eye is only for _____________________

Right Option : C
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Question : 2

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

Right Option : A
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Question : 3

Which of the following are correct :

(a) In dim light, the iris widens the pupil to admit more light into the eye.

(b) In bright light, it  contracts the pupil so that less light goes in.

(c) In bright light, it widens the pupil so that less light goes in.

Right Option : A
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Explanation
 
 


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