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Scattering of Light and Tyndall Effect

  • Last Updated : 21 Jul, 2021
Geek Week

Tyndall effect, also known as the Tyndall phenomenon, is the scattering of a light beam by a medium containing tiny suspended particles—for example, smoke or dust in a room—which makes a light beam entering a window visible. Short-wavelength blue light is dispersed more strongly than long-wavelength red light, similar to Rayleigh scattering. Let’s first understand the concept of scattering.

Scattering of light

Scattering is the mechanism through which light is transmitted in all directions when it strikes a particle with a larger diameter.

The source of light may be explored completely. When light moves from one medium to another, such as air or a glass of water, a portion of the light is absorbed by the medium’s particles, followed by subsequent radiation in a specific direction. Scattering of light is the term for this phenomenon. The intensity of scattered light is determined by particle size and wavelength.

Because of the waviness of the line and its interaction with a particle, shorter wavelengths and high frequencies scatter more. The more wavy a line is, the more likely it is to intersect with a particle. Longer wavelengths, on the other hand, have a lower frequency, are straighter, and have a lower likelihood of colliding with the particle, therefore the chances are lower.

Rayleigh’s Law of Scattering



It states that the probability for scattering will give a high rise for a shorter wavelength, and it is inversely proportional to the fourth power of the wavelength of radiation.

Let p be considered as the amount of dispersed light and λ is the wavelength

p ∝ 1λ4

Therefore, light scattering decreases as wavelength increases. When some particles are more effective at scattering a specific wavelength of light, this is known as Rayleigh scattering. Because air molecules, such as oxygen and nitrogen, are tiny, they are more efficient at scattering shorter wavelengths of light (blue and violet).

Tyndall Effect

Smoke, water droplets, dust, and other minute particles make up the earth’s atmosphere. The path traveled by a ray of light when it encounters these small particles becomes apparent. These particles continuously reflect light, which then reaches us. The Tyndall effect is the phenomenon of light scattering by particles. The size of the scattering particles determines the color of the scattered light.

Tyndall effect refers to the scattering of light by particles in its path. When sunlight penetrates through the canopy of a thick forest, the Tyndall effect is also visible.

Tyndall found that when white light with seven colors is transmitted through a transparent liquid containing tiny suspended particles, the blue color of white light with the shorter wavelength is dispersed considerably more than the red color with the longer wavelength.

Thus, when a light beam is transmitted through a colloidal solution in a dark environment, the route of the light is lit when seen through a microscope positioned perpendicular to the direction of light. The Tyndall effect is the name given to this phenomenon.



Causes of Tyndall Effect

  • The colloidal particle is bigger than the solute particle in a real solution. 
  • Colloidal particles absorb energy from incoming light and then disperse some of it off their surfaces.
  • Thus, the Tyndall effect is caused by light scattering by colloidal particles, and the colloidal particles may be seen moving as points of light moving against a black backdrop.

Examples of the Tyndall Effect

  • The path of light becomes evident when a torch is turned on in a foggy atmosphere. The light scattering in this scenario is caused by water droplets in the fog.
  • Opalescent glass has a bluish appearance when viewed from the side. However, orange-colored light emerges when light is shined through the glass.
  • We are able to see dust particles when a single ray of light enters a dark room.
  • Milk is a colloid that contains globules of fat and protein. When a beam of light is directed at a glass of milk, the light is scattered. This is a great example of the Tyndall effect.
  • The Tyndall effect is the phenomenon of light scattering by particles in a colloid or an extremely tiny solution.

Some Daily phenomena based on Tyndall Effect

  1. Blue Color of the Sky: The blue color of the sky is caused by the dispersion of the blue component of white sunlight by air molecules in the atmosphere. The sunlight is made up of seven different colored lights that are blended together. The size of air molecules and other tiny particles in the atmosphere is smaller than the wavelength of visible light. These scatter light of shorter wavelengths at the blue end more effectively than light of longer wavelengths at the red end. The wavelength of red light is approximately 1.8 times that of blue light. As a result, as sunlight travels through the atmosphere, tiny particles in the air scatter blue (shorter wavelengths) more strongly than red (longer wavelengths). Our eyes are filled with dispersed blue light. Because there is no atmosphere in deep space to scatter sunlight, the sky appears dark and black rather than blue. At those heights, scattering is minimal.
  2. Red appearance of Sun during Sunset and Sunrise: Before reaching our eyes, light from the Sun near the horizon travels through deeper layers of air and a greater distance in the earth’s atmosphere. The light from the Sun overhead goes a shorter distance. As a result, around midday, the Sun looks white because only a little amount of blue and violet light is dispersed. The size of air molecules and other tiny particles in the atmosphere is smaller than the wavelength of visible light. These scatter light of shorter wavelengths at the blue end more effectively than light of longer wavelengths at the red end. When the sun is near the horizon at sunrise and sunset, it has to travel the maximum distance through the atmosphere to reach us. The majority of the shorter wavelength blue-color and shorter wavelengths contained in sunlight are dispersed out throughout its long voyage. As a result, the light that reaches us has longer wavelengths. As a result, the sun appears crimson red.
  3. Blue color of our Eyes: The primary difference between blue, brown, and black colored irises is the amount of melanin in one of its layers. The layer in a blue iris has relatively lower amounts of melanin in it when compared to a black iris, making it translucent. When light is incident on this translucent layer, it is scattered due to the Tyndall effect. Because blue light has a shorter wavelength than red light, it is more easily dispersed. Unscathed light is absorbed by a deeper layer of the iris. Because the bulk of the dispersed light is blue, these irises get their distinctive blue color.

Sample Problems

Problem 1: What is Tyndall Effect?

Solution:

Smoke, water droplets, dust, and other minute particles make up the earth’s atmosphere. The path travelled by a ray of light when it encounters these small particles becomes apparent. These particles continuously reflect light, which then reaches us. The phenomenon of light scattering by particles is known as the Tyndall effect.

Problem 2: Why does the Sky appear clear blue?

Solution:

The sky appears blue because violet, indigo, and blue colours interact with suspended particles when white light flows through the atmosphere. These waves are absorbed, then diffused, and our eyes receive them.

Problem 3: Why the color of Sunrise and Sunset appears to be red?

Solution:

The color of the sun and its surroundings appear crimson at sunset and sunrise. Because the sun is near the horizon at sunset and sunrise, the sunlight must travel a greater distance through the atmosphere. As a result, the particles scatter the majority of the blue light (shorter wavelength). Longer wavelength light (red color) penetrates human eyes. This is why the sun appears to be red.



Problem 4: Why red color is used to make a danger signal or sign?

Solution:

Because red has the longest wavelength, it scatters the most when it hits minuscule particles of fog and smoke (visible spectrum). As a result, we can see the red color vividly even from a great distance.

Problem 5: Why does the Sun appear yellow?

Solution:

The sun appears yellow because violet, indigo, and blue colors are distributed across the upper atmosphere, resulting in yellow light. This light appears yellow as it enters our eyes.

Problem 7: Why does the sky appear dark instead of blue to an astronaut?

Solution:

An astronaut sees the sky as dark rather than blue: There are no particles in space, hence there is no scattering. As a result, the sky appears to be gloomy.

Problem 7: Why does the smoke coming out of the coal-fired chimney appears blue on a misty day?

Solution:

On a misty day, the smoke from a coal-fired chimney appears blue because the microscopic particles of smoke and moisture scatter blue light traveling through it. The smoke appears blue when this blue light reaches human eyes, and the sky appears dark instead of blue to an astronaut. There are no particles in space, hence there is no scattering. As a result, the sky appears to be gloomy.

Problem 8: Why does the driver use orange lights rather than normal white lights on a foggy day?

Solution:

When a driver drives in fog while using white light, the tiny droplets of water scatter a lot of blue light. When this diffused blue light reaches the eyes, it reduces visibility, making driving extremely difficult. Orange light, on the other hand, does not scatter due to its longer wavelength, allowing the driver to see clearly.

Problem 9: How is the Tyndall Effect Responsible for Blue Eye color?

Solution:

The quantity of melanin in one of the layers of the iris is the primary distinction between blue, brown, and black irises. When opposed to a black iris, the layer of a blue iris contains a smaller quantity of melanin, making it translucent. The Tyndall effect scatters light when it is incident on this translucent layer. When opposed to red light, blue light has a shorter wavelength and is hence scattered more. Unscattered light is absorbed by a layer deeper in the iris. Because the majority of the scattered light is blue, these irises take on a distinctive blue hue.

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