Optical instruments are used to see minute objects or specimens that our naked eye cannot see. What type of lens is used for each optical instrument? Why do you think it is the best type of lens to be used?
Answers
Answer:
The Eye
The human eye is an optical instrument that enables us to view all the objects around us is a very complex organ. Let us study the structure of the human eye. The white protective membrane seen when looked into the eye directly is a Sclera. It is tuff, opaque and fibrous outer layer of the eyeball.
The circular part is the Iris. The color of the eye is determined by the color of the iris. The center transparent area of the iris is the Pupil. The iris works like the shutter of the camera. It absorbs most of the light falling on it and allows it to pass through the pupil.
The amount of light that enters the inner part of the eye depends on the size of the pupil. In bright light, the iris contracts the pupil to restrict the light, whereas in low light it widens the pupil to emit more light into the eye. The eyeball is spherical in shape. The retina of the eye is able to detect the light and its color because of the presence of senses known as rods and cones.
Light entering the human eye is first refracted by the cornea. The refracted light is then incident on an iris. The lens is just behind the iris and light after refracted through the pupil falls on it and forms a sharp image. Image formation exactly on the retina enables us to see the object clearly.
Defects in Human Eye
Like the ability to focus diminishes with the age of a person and this defect is Presbyopia. This defect is corrected by using converging lenses. The other defect is Hypermetropia. It is observed in the people of any age. The person suffering from this defect will have a normal vision while looking at the far object. But the vision is blurred for nearby objects. This is corrected by using a convex lens.