Page 1 - LN
P. 1

SAI INTERNATIONAL SCHOOL
                                                         Class 8
                                                     Lesson notes
                                                   Subject-Physics
                                                        CH- Light
                                        Subtopic- Features of Human Eye


               Blind Spot:
               The junction of retina and the optic nerve is called the blind spot. There is no
               photosensitive cell at this spot, and hence no image is formed at this spot on the retina.

               PERSISTENCE OF VISION:
               An image stays on the retina for about 1/16th of a second. This feature is called
               persistence of vision. Due to this, when many still images (more than 16 frames per
               second) are shown in a sequence, they give the illusion of moving images. Movies and
               animation are made by exploiting this property of the human eye.

               Near point
               Minimum distance at which the eye can see objects distinctly. It varies with age. For a
               healthy eye its value is 25 cm.

               Far Point
               Maximum distance at which the eye can see objects distinctly. Its value for an healthy
               eye is infinite.

               Care of Eyes
               Eyes are very important organ and they are sensitive too. So, proper care of eyes is
               very important. Some tips for care of eyes are as follows:
               1. Do not read in too bright or too dim light.
               2. Do not look directly at a bright object or at the sun.
               3. Do not keep the book too close to your eyes, while reading. Don’t keep the book too
                    far either.
               4. If something gets into the eye, do not rub the eye. Wash it with cold water.
               5. In case of any problem like itching or burning sensation, consult an ophthalmologist.
                    A doctor who specializes in the disease of eyes is called an ophthalmologist.

               Suggested Activity
               NCERT textbook activity 16.9: Observing blind spot in the eye
               Activity 16.10: Observing Persistence of vision
   1