Science project idea on why eyeglasses are used by some persons.
Eyeglasses Science Project Idea
Why eyeglasses are used by some persons.You all know people who without glasses must hold a book very close to the eyes in reading.These nearsighted persons have trouble in seeing distinctly anything which is more than a few feet from them.On the other hand, you may have friends who are farsighted; who can read signs at a greater distance than you can, but who have trouble in reading a book or newspaper held at the ordinary reading distance from the eye.Nearly all persons, as they grow older, become farsighted; and you will notice that many begin to wear glasses at about the age of forty or even much younger. By the use of glasses both the nearsighted and the farsighted are enabled to see as well as those who are not troubled by these eye defects.To understand how glasses are able to bring about this change, it is necessary to know how the rays of light act in entering the eye. How a Picture or Image is Formed in the Eye In the condition of the normal eye, it will be noticed that the rays of light are bent as they strike the curved surface of the cornea, and again as they pass through the crystalline lens, finally coming to a focus on the nervous layer, the retina, lining the back of the eye cavity.This is the same process that takes place in a camera when the rays of light coming from an object are bent by the lens of the camera and focused on the sensitive film or plate.
How Light is Bent in Passing From One Substance into Another
The ability of a lens to bend the rays of light is very well illustrated by a burning glass, with which the parallel rays of the sun may be focused on one point, producing enough heat there to burn a piece of paper. Light may be considered to be made of a column of transverse vibrations.These are slowed as they pass into a denser substance like glass.You can easily understand how the column will be bent if the glass is entered at an angle.In the same way, as the ray of light passes from the glass into the air again, it will be bent.This bending of the rays of light, in passing from one substance into another, called refraction, explains the fact that a stick, projecting at an angle from the water, appears to be bent at the point where it leaves the water. How The Eye is Able to Focus on Near and Distant Objects
You will wonder how we can focus the eye upon a distant object, and then without any appreciable effort, focus it upon something near.The power of accommodation may be illustrated as follows. Focusing by the Eye Science Experiment
Hold a pencil before your eyes and read the label on it.How does a picture on the opposite side of the room appear?Still keeping the pencil in the same position, look at the picture. How does the pencil appear now? In a camera, such a change in focus is brought about by moving the lens closer to or farther from the sensitive film.In the case of the eye, it is of course impossible to change the distance between the lens and the sensitive inner coat of the eye, the retina.The same result, however, is accomplished by changing the shape of the lens.This is done by muscles which are connected with a tough membrane or ligament in closing the lens.The muscle by its contraction flattens the lens, with the following result. When near objects are to be looked at, the muscles relax and the lens, because of its elasticity, becomes more convex and the object is focused upon the retina. Cause and Correction of Farsightedness and Nearsightedness As a person becomes older, the lens loses its elasticity and it becomes impossible for him to see near objects distinctly, although his power of seeing things at some distance remains unimpaired.You can easily see how the use of slightly convex glasses will do the work that the flat lens of his eye will not do, enabling him to see, for example, the print of a book as well as before the lens began to lose its elasticity. Farsightedness, not the result of age, is usually due to the fact that the eyeball is too short. This condition can be corrected by the use of convex glasses.Explain. Nearsightedness, on the other hand, is usually caused by the eyeball being too long.In this case the image of an object held at the normal reading distance, or at any distance farther away, is formed in front of instead of on the retina. This condition can be corrected by the use of concave eyeglasses.Explain. What is Astigmatism and How is it Corrected? Many persons who are neither farsighted nor nearsighted must wear glasses or suffer from headaches.This is caused by a defect of the eye called astigmatism, which results from the unequal curvature of the cornea (the front of the eyeball).What effect will this have upon the bending of the different rays of light that enter the eye?The glasses for these eyes are curved in such a way that the defects of the cornea are counteracted.If glasses are not worn, the ciliary muscle in its effort to bring about a condition which will result in a clearer image is overworked and eyestrain and headache result. If you are troubled with eyestrain or headache after using the eyes for some time, have your eyes examined at once by a competent oculist or optometrist.Eyestrain results in both discomfort and lessened efficiency.Frequently headaches, nervousness, and other troubles are relieved as by magic when eyestrain has been removed by the use of proper glasses.
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