Tyndall Effect: Dispersion of Light

A colloid is a heterogeneous system of the dispersed phases and the dispersion medium. The dispersed phase consists of very fine particles suspended into a dispersion medium. The dispersed phase consists of an aggregate of atoms, ions, or molecules or a single macromolecule such as proteins.

Tyndall effect is a phenomenon in which colloidal particles (dispersed phase) scatter the beam of light subjected towards them. The Tyndall effect is mainly shown by all the colloidal solutions. Tyndall effect can be used to verify whether the solution is colloid or not.

Tyndall effect mainly depends on:

1. The density of the colloidal particle.

2. The frequency of the light incident.

In this article, we will study Tyndall Effect Dispersion of Light in detail.

Tyndall Effect

Whenever a beam of light is passed through a colloidal solution, particles of the colloidal solution do not allow the light to pass through it deviates from its original path i.e straight line, and gets scattered. The scattering of light through the colloidal solution is shown below:

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The scattering of light depends on the wavelength. The extent of scattering increases with the shorter wavelength and decreases with a higher wavelength. As blue light has a shorter wavelength as compared to red light, the extent of scattering is more in blue than red light. Sometimes the smoke released from the vehicles appears to be blue, this is due to the shorter wavelength of blue light.

The Tyndall Effect Dispersion of Light was first observed by the Irish physicist John Tyndall (and is named after it). The particle diameters causing the Tyndall effect can range from 40 nanometers to 900 nanometers (1 nanometer = 10^-9 meters). The wavelength of the visible light spectrum ranges from 400 to 750 nanometers in contrast.

Tyndall Effect Dispersion of Light Examples:

1. Milk is a colloid containing fat and protein globules. The light is scattered when a beam of light is aimed at a glass of milk.

2. The direction of the light becomes evident when a torch is turned on in a foggy atmosphere. The water droplets in the fog are responsible for the scattering of light in this case.

Applications of Tyndall Effect:

1. The sky appears blue - When the sunlight reaches the earth’s atmosphere, it interacts with the gaseous particles present in the air. As the light strikes, it gets scattered in all directions in the atmosphere. Blue light scatters the most due to its shorter wavelength hence the sky appears to be blue.

2. At sunrise and sunset, when light travels the long path to reach our eyes, blue light is removed due to its shorter wavelength. So, light with the highest wavelength i.e red and yellow gets scattered by gaseous molecules present in the atmosphere and hence sunrise and sunset appear red.

3. The different colors like blue, brown, and black of the iris are due to the production of melanin. In the blue iris, melanin produced is comparatively less than that of the black iris, making it translucent. Light gets scattered as it falls on the translucent layer. As blue light has a shorter wavelength, it is dispersed to a greater degree compared to red light. The unscattered light is absorbed by another layer deeper in the iris. Since the majority of the dispersed light is blue, the typical blue color of these irises is obtained.

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