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(a) Draw a simple diagram of the human eye and label clearly the cornea, iris, pupil, ciliary muscles, eye-lens, retina, optic nerve and blind spot.(b) Describe the working of the human eye with the help of the above diagram.(c) How does the eye adjust itself to deal with light of varying intensity?
(a) The diagram of the human eye given below, showing clearly the cornea, iris, pupil, ciliary muscles, eye-lens, retina, optic nerve, and blind spot.
(b) Working of the human eye:
The light rays coming from an object enter the eye through the cornea, a transparent substance. Just behind the cornea is the iris, a flat, coloured, ring-shaped membrane that has a hole in the middle called the pupil. The light passes through the pupil and fall on the eye lens which is a convex lens, so it converges the light rays to produce a real and inverted image of the object on the retina. The retina of our eye contains a large number of light-sensitive cells that respond to light and generates electric signals. These signals are conveyed to the brain by the optic nerve, which then gives rise to the sensation of vision.
(c) The eye adjusts itself to deal with light of varying intensity with the help of the iris, which automatically adjusts the size of the pupil according to the intensity of light received by the eye. If the intensity of light is high, then iris contracts the pupil so as to reduce the amount of light entering the eye. Also, if the intensity of light is low, then iris expands the pupil to allow more light to enter the eye.
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