How Does Tyndall Effect Work

All of us enjoy the vibrant colours seen in the sky at sunset. on clear days, we can see a blue sky during the daytime; however, the setting sun paints the sky in an orange gleam. If you visit the beach during a clear evening, you will see the part of the sky around the setting sun is spread with yellow, orange and red even though some part of the sky is still blue. Have you ever wondered how nature could play such clever magic and deceive your eye? This phenomenon is caused by Tyndall Effect.

This article explains,

1. What is Tyndall Effect
2. How Does Tyndall Effect Work
3. Examples of Tyndall Effect

What is Tyndall Effect

In simple terms, Tyndall Effect is the scattering of light by colloidal particles in a solution. To understand the phenomena better, let’s discuss what colloidal particles are.

Colloidal particles are found within the size range of 1-200 nm. The particles are dispersed in another dispersion medium and are called dispersed phase. Colloidal particles are usually molecules or molecular aggregates. These can be separated into two phases if required time is given, hence, are considered metastable. Some examples of colloidal systems are given below. (Read more about Colloids here.)

Dispersed Phase: Dispersion medium	Colloidal System- Examples
Solid: Solid	Solid sols – minerals, gemstones, glass
Solid: Liquid	Sols – muddy water, starch in water, cell fluids
Solid: Gas	Aerosol of solids – Dust storms, smoke
Liquid: Liquid	Emulsion – medicine, milk, shampoo
Liquid: Solid	Gels – butter, jellies
Liquid: Gas	Liquid Aerosols – fog, mist
Gas: Solid	Solid foam – stone, foam rubber
Gas: Liquid	Foam, Froth – soda water, whipped cream

The tiny colloidal particles have the ability to scatter light. When a beam of light is passed through a colloidal system, the light collides with the particles and scatter. This scattering of light creates a visible light beam. This difference can be clearly seen when identical light beams are passed through a colloid system and a solution.

When light is passed through a solution with particles in the size of < 1 nm, the light directly travels through the solution. Hence, the path of the light cannot be seen. These types of solutions are called true solutions. In contrast to a true solution, the colloid particles scatter the light, and the path of the light is clearly visible.

Figure 1: The Tyndall effect in opalescent glass

There are two conditions that must be fulfilled for the Tyndall Effect to occur.

The wavelength of the light beam used should be larger than the diameter of the particles involved in scattering.
There should be a huge gap between the refractive indices of the dispersed phase and the dispersion medium.

Colloidal systems can be differentiated by true solutions based on these factors. As true solutions have very small solute particles which are indistinguishable from the solvent, they do not satisfy the above conditions. The diameter and the refractive index of solute particles are extremely small; hence, solute particles cannot scatter light.

The above-discussed phenomenon was discovered by John Tyndall and was named as Tyndall Effect. This applies to many natural phenomena we see on a daily basis.

Examples of Tyndall Effect

The sky is one of the most popular example to explain Tyndall Effect. As we know, the atmosphere contains billions and billions of tiny particles. There are innumerable colloidal particles among them. The light from the sun travels through the atmosphere to reach the earth. The white light consists of various wavelengths that correlate to seven colours. These colours are red, orange, yellow, green, blue, indigo and violet. Out of these colours, the blue wavelength has a greater scattering ability than others. When light travels through the atmosphere during a clear day, the wavelength corresponding to the blue colour gets scattered. Therefore, we see a blue sky. However, during the sunset, the sunlight has to travel a maximum length through the atmosphere. Due to the intensity of scattering of the blue light, the sunlight contains more of the wavelength which corresponds to red light when it reaches earth. Hence, we see a reddish-orange colour shade around the setting sun.

Figure 2: Example of Tyndall Effect – Sky at Sunset

When a vehicle travels through the fog, its headlights do not travel a long distance as it does when the road is clear. This is because the fog contains colloidal particles and the light emitted from the headlights of the vehicle gets scattered and prevents light from traveling further.

A tail of a comet appears bright orangish yellow, as the light is scattered by the colloidal particles that remain in the path of the comet.

It is evident that Tyndall Effect is abundant in our surroundings. So next time when you see an incident of light scattering you know that it is because of Tyndall Effect and colloids are involved in it.

Reference:

Jprateik. “Tyndall Effect: The Tricks of Scattering.” Toppr Bytes. N.p., 18 Jan. 2017. Web. 13 Feb. 2017.
“Tyndall Effect.” Chemistry LibreTexts. Libretexts, 21 July 2016. Web. 13 Feb. 2017.

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