Concepts

Class 10
Chapter 11 Class 10 - Human Eye and Colourful World

Tyndall Effect is the scattering of light by particles in its path like dust,water molecues etc

Explanation

We know that atmosphere is a mixture of several gases, dust particles, smoke, water particles etc

When sun light falls on the atmosphere,light particles get reflected from surface of these particles and get scattered in different directions

This is called Tyndall Effect

## Examples of Tyndall Effect

Example 1

When a small ray of sunlight enters a dark room

We are able to see dust particles in the air

This is due to Tyndall Effect

It is because rays of sunlight are reflected off the surface of these dust particles and move in different directions

Example 2

In a dense forest, sunlight is not able to reach down because of shadow of number of trees

If some light is able to pass down from canopy of forest (upper layer of leaves of forest),we see scattering of light

This is because sunlight gets scattered off the water particles in the air

## Activity to show Scattering of Light

Equipment Required

We take a Source of Light S

We take a water tank T and fill it with water

We take one Lens L1 and place it between S and T

On the other side of tank, we place a cardboard containing whole at center

We take another lens and place it on right of cardboard hole

We place a screen on the other side of lens

Procedure

When we switch on source of light,

Light Rays first fall on lens, then water tank, then from cardboard enter the other lens and finally hit the screen

We see that there is no scattering of light currently

Now, we dissolve 200 gm of hypo (sodium thiosulphate) and 1-2 ml of concentrated sulphuric acid into tank

We see the suphur particles forming in the tank

Now light rays reflect form this suphur particles

So 3 side of tank becomes blue

The right side first appears orange red color and then bright red color

Red colored image is formed on screen

Summary

Hence we can say that forming of red light on screen is because of tyndall effect

It is due to reflection of light rays on striking the suphur particles

Since most of blue color gets scattered, red color light rays ultimately reach the screen