[Physics Class Notes] on Rayleigh Scattering Pdf for Exam

Rayleigh Scattering is an interesting phenomenon that talks about the elastic scattering of light or electromagnetic radiations by molecules of gas that are smaller than the wavelength of the light or the radiation, sometimes scattering is possible by solid (dielectric scatterers), and liquid also.  

This scattering of light was first noticed by a 19th-century British physicist named “Lord Rayleigh,” in the year 1871 when Rayleigh published two papers on the colour and polarization of skylight to evaluate Tyndall’s effect in water droplets regarding the small particulates’ volumes and refractive indices, and therefore, the phenomenon was named Rayleigh Scattering (Lord Rayleigh Scattering).

On this page, you will get a sufficient explanation of what is Rayleigh Scattering, Rayleigh Scattering law, and Rayleigh Tyndall Scattering.

Now, let’s get insight into the history of the Rayleigh Effect:

History of Scattering of Light

In 1869, while endeavouring to decide if any containments stayed in the purified air, John Tyndall utilized for infrared investigations, he found that brilliant light dissipating off nanoscopic particulates was faintly blue-tinted.

He found that a similar scattering of light gave the sky its blue colour, however, he was unable to clarify the inclination for blue light, nor could atmospheric residue clarify the intensity/power of the sky’s tone. 

In 1871, a 19th-century physicist named Lord Rayleigh publicized two papers on the colour and polarization of skylight to measure Tyndall’s impact on water drops in terms of the small particulates’ volumes and refractive indices. 

In 1881 with the advantage of James Clerk Maxwell’s 1865 proof of the electromagnetic idea of light, he showed that his conditions followed from electromagnetism. 

In 1899, he demonstrated that they applied to individual molecules, with terms containing particulate volumes and refractive indices supplanted with terms for molecular polarizability.

Now, we will understand what is Rayleigh Scattering in detail:

State Rayleigh’s Law of Scattering

At the point when electromagnetic light proliferates through the air, at that point, the to-and-fro motion of electrons inside the particles of the medium (air) produces a wavering electric field inside it. 

Thus, when photons are permitted to send through these molecules then a few photons get absorbed yet then retransmitted in various directions by the air molecules. This natural phenomenon is known as Rayleigh Scattering and the study of this phenomenon is known as Rayleigh Scattering Law.

Rayleigh Scattering Example

For instance, the colour of the sky is blue because of the scattering of sunlight by the atmosphere.

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Point to Note:

The strength of scattering relies on the wavelength of light/radiation and the particle size liable for scattering.

Interesting Fact: 

It is essential that dispersing/scattering doesn’t happen because of the collision, rather it is the aftereffect of the electromagnetic interaction among photons and the particles of the medium.

What is Rayleigh Scattering?

From the above text, we understood the beautiful and interesting natural phenomenon via Rayleigh Effect. 

Now, let us explain Rayleigh scattering:

We realize light particles strike a molecule of air during propagation. At that point, the electromagnetic field of the incident light reallocates the molecular charges. This causes the vibration of the molecules and the charges begin oscillating with the radiation frequency. 

Yet, this interaction to some degree changes the polarization of incident light. Because of this, a portion of the light energy gets absorbed by the molecules of the air. This energy is then re-emanated in various directions that prompt cause scattering of light, more explicitly, named Rayleigh Scattering.

Rayleigh Scattering Law

Rayleigh Scattering law expresses that the amount of scattering of light is conversely relative to the fourth power of the wavelength. 

The mathematical form of the above statement is:

 I = [frac{1}{lambda^{4}}]

Here,

I  = intensity

[lambda] = wavelength 

This suggests that in the case of a shorter wavelength, then more likely, the light is bound to be scattered in contrast with longer frequency, because of the inverse relationship between the two.

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The blue colour of the sky:

We realize that the wavelength of the blue colour is less than the red colour. In this way, because of the shorter wavelength, blue light scatters comparatively more than red light. This is the reason why the sky seems blue rather than some other colour.

Rayleigh Scattering in Optical Fibre

The scattering of transmitted light through an optical fiber is the consequence of inhomogeneities and imperfections in fiber at the hour of creation. As we realize that glass fiber is a composition of irregular connection of molecules. 

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Because of this explanation, a few regions in the structure may contain either high or molecular density. This prompts the variation in the refractive index of the material at different points inside the fiber. 

The variation in the refractive list prompts Rayleigh scattering of the transmitted light. 

Essentially, the light rather than being retained is emanated in various directions consequently named as a scattering of light.

Now, let’s identify the comparison between the Rayleigh Effect and the Tyndall Effect:

Rayleigh Tyndall Scattering

Rayleigh scattering is characterized by a mathematical formula that needs a light-scattering particle to be far smaller than the light’s wavelength.

For dispersion of particles to qualify for the Rayleigh formula, the molecule sizes should be underneath approximately 40 nanometres (for noticeable light), and the particles might be individual molecules. 

Colloidal particles are greater and are in the rough area of the size of a wavelength of light. 

The Tyndall effect was named after 19th-century physicist John Tyndall. Tyndall scattering, for example, colloidal particle scattering, is significantly more intense than Rayleigh scattering because of the greater particle sizes involved. 

The significance of the particle size factor for intensity can be found in the enormous exponent it has in the mathematical statement of the intensity of Rayleigh dispersing. 

On the off chance that the colloid particles are spheroid, Tyndall dispersing can be numerically examined as far as the Mie Theory, which concedes particle sizes in the rough area of the frequency of light. 

Therefore, light scattering by particles of complex shape is depicted by the T-matrix strategy.