The human eye is optically very similar to camera. An enclosure,the eye ball itself ,contains a lens-shaped organ whose focal length can be shortened by ciliary muscles capable of squeezing it into a thicker shape. The cornea is a curved transparent membrane in the front of the eye ball. Refraction takes place here. A watery fluid in front of the lense and a jelly behind it contribute to the refraction producing an image on the ratina is inverted. The ratina contains millions of delicate nerve endings whose sensations are carried to the brain. The iris is a variable-sized diaphragm controlling the amount of light entering the eye through the pupil, and thus protects the retina from damage.
The images of the objects at different distances from the eye are brought to focus on retina cy changing the focal length of the eye-lense. The ciliary muscles change the thickness of the eye-lens.
A thicker lens has lesser radius of curvature and hence smaller focal length. In this manner, by changing the focal length of the eye lens, the images of object at different distance are brought to focus on the retina.
Hence , in this way , we see an objects ,and various things those are lies in our surroundings.
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