Activity 16.9 Class 8 Science Chapter 16 Solution

we will go through activity 16.9 class 8 science chapter 16 Light in which we will discuss the blind spot on the retina. You should also go through activity 16.6 to get more about reflection.

Activity

   ·     Make a round mark and a cross on a sheet of paper with the spot to the right of the cross.

   ·     The distance between two marks may be 6-8 cm.

   ·      Hold the sheet of paper at an arm’s length from the eye.

   ·   Close your left eye.

  ·     Look continuously at the cross.

  ·      Move the sheet slowly towards you, keeping your eye on the cross.

   ·     What do you find?

   ·     Does the round mark disappear at some point?

   ·     Now close your right eye.

   ·      Look at the round mark now and repeat the activity.

   ·     Does the cross disappear?

   ·     The disappearance of the cross or the round mark shows that there is a point on the retina that cannot send messages to the brain when light falls on it.

Observation and explanation

There is a thin layer of neural tissues inside the eye which called the retina. It has numerous lights detecting cells called photoreceptors.

When light falls on the retina where it is converted into electric impulses. These electric impulses to the brain through the optic nerve.

The blind spot is the area where the optic nerve connects to the brain and it has no light-sensitive cells, so we can’t see anything if the light coming from an object falls on the blind spot.

When we move the sheet keeping eye on a cross or round mark, we cannot see these ‘ cross or round marks’ at a certain position.

Why this happens?

Because at a certain position, light from the object falls on the blind spot where no light-detecting cells are present so the light is not converted into electric impulses.

Conclusion

The blind spot is a region on the retina that does not have any light-detecting cells so images formed on this part of the retina cannot be seen.

Related Topics

1. Activity 16.10

2. Activity 16.8