Page 1 - LN
P. 1

SAI INTERNATIONAL SCHOOL
                                                          Class8
                                                     Lesson notes
                                                   Subject-Physics
                                                        CH- Light
                                          Subtopic- Parts of Human Eye
        Human Eye
          Eyes are the sense organs which give us the sense of vision. The human eye is almost spherical
          in shape. Following are the main structures in the human eye.



































         Cornea: The eyeball is covered with a tough layer. This layer is transparent in the front. This
            transparent portion is called cornea.
         Iris: Iris is a thin circular structure. It works like the shutter of a camera. It controls the amount of
            light entering the eye. The colour of iris imparts distinct colour to the eyes of an individual. A
            person with blue iris has blue eyes.
         Pupil: There is a hole in the centre of iris. This is called pupil. Light enters the eye through the
            pupil. When the light is bright, iris contracts and thus allows less light into the eye. When the
            light is dim, iris dilates and thus allows more light into the eye.
         Lens: Lens is present behind the pupil. The lens in the human eye is a convex lens. The size
            and thickness of the lens changes to change the focus as per the distance of an object.
         Retina: Retina is at the back of the eye and marks the inner layer of the eyeball. Images are
            formed on the retina and thus it works like a screen. There are photosensitive cells in the retina.
            These cells are of two types, which are as follows:
              Cone Cells: The cone cells are sensitive to bright light. They also give the sense of
               colour.
              Rod Cells: The rod cells are sensitive to dim light.
         Optic Nerve: The optic nerve emerges from the back of the eye ball. This nerve goes to the
            brain.
        Suggested Activity NCERT Textbook activity 16.8: To observe the change in size of the pupil.
   1