What is the Scattering of Light?
There is some form of radiation that deviates from its straight path due to the non-uniformities in the medium. This process of deviation is called Scattering.
Example- Scattering of Light.Light is the most crucial part of everyone's life. It exists in tiny packets called photons. In this article, we will discuss the Scattering of Light. We will also know why the colour of a clear sky is blue and the colour of the clouds is white.
Scattering of Light
The scattering of light is one of the most important phenomena in daily lives. This phenomenon has been seen by everyone from their childhood like the blue colour of the sky, the colour of the rainbow, etc. The scattering of light is completely different from the reflection and refraction of light. In reflection of light, the light goes in a straight line whereas in the scattering of light the light ray gets scattered in different directions by the medium through which it passes.
The process by which small particles are present in the atmosphere causes the scatter in the light which in turn gives rise to optical phenomena such as the blue colour of the sky in which we term as the scattering of light.
Though not an appropriate means of study still Maxwell equation gives the basis of theoretical as well as computational methods in order to describe light scattering. Due to the lack of precision, it is mainly described on the basis of computational electromagnetics which deals with electromagnetic radiation scattering and absorption by particles.
When a light ray passes through a medium, it strikes the particles present in them. Due to this, some of the rays get absorbed while some get scattered in all directions.
Example- When light strikes the particles in the air, the particles absorb some light and radiate the rest in all directions except the incident direction. This is called "scattering of light". The wavelength of the light and the size of the particle which scattered the light assists in determining the strength of the scattering.
For example, when the sun rays enter the earth's atmosphere it strikes the particles which are present in the atmosphere. Some of these rays are absorbed by the particles and some are scattered in all directions. This can be seen from the given figure. Therefore, it can be said that the light can get deflected from the incident path due to particles, irregularities, or interference between the two media. Hence, shorter wavelengths and high-frequency light result in more scattering.
There are several Examples of Scattering of light but the Two Main Examples of the Scattering of light are:
Reflection from rough surface
Reflection, refraction, or diffraction through impurities in the volume
Random Reflection from a Rough Surface
All the surfaces in the environment are rough. The roughness of the surface and wavelength will describe the amount of light that is scattered. The rougher the surface, the more is the absorption of light. Also, it will scatter in different directions depending upon the wavelength of the light. The roughness of cars and pieces of jewellery are the best examples of random reflections from rough surfaces.
Reflection through the Presence of Impurities in Volume
Here, the light gets scattered by the charged particles. There are different types of scattering of light:
Rayleigh scattering
Mie scattering
Electromagnetic scattering
Rayleigh Scattering
Rayleigh scattering is named after the 19th-century physicist Lord Rayleigh. It is the elastic scattering of light from the particles having a size less than the wavelength of the incident light. The sky looks blue due to this as the red colour has a large wavelength so it doesn't get scattered. Signal scattering through the optical fibre follows this phenomenon.
Mie Scattering
This scattering is Mie’s solution to Maxwell's equation. In this type of scattering the size of the particle is more than the wavelength of the light. Hence, there is a non-uniform scattering. It is also an elastic type of scattering. Example-The sky looks blue and cloud white due to this, the fog and water droplets’ colour is also the result of this type of scattering.
Electromagnetic Scattering
Electromagnetic scattering is a common type of scattering where electromagnetic waves get deflected continuously. It is of Two Types:
Elastic Scattering
Inelastic Scattering
Elastic scattering includes Rayleigh and Mie type of scattering whereas Raman and Compton’s scattering is Inelastic scattering.
The Factors on Which Scattering of Light Depends are as Follows
The size of the molecule or particle by which the light is scattered.The wavelength of the incident light. If the wavelength of the incident light which strikes the earth's surface has less wavelength and more frequency as in the case of blue colour then it gets scattered more. While if the incident light has a large wavelength and small frequency as in the case of red color then it is deflected less.
The relation between the probability of scattering of light and wavelength of light is
p ∝ 1/λ4
Where
p= probability of scattering of light
λ= wavelength of the light
It is clear from the above equation that the probability of scattered light is higher for the light having a shorter wavelength as the probability is inversely proportional to the fourth power of the wavelength.
Application of Scattering of Light
There is a huge range of applications of light scattering known to date. They can be listed as follows:
The sky appears blue as the light gets scattered by the particles present in the atmosphere.
During sunset and sunrise, the sky appears red due to the scattering of light.
In projectors
In medical.
It provides a brief account of the size, shape, number, and time independence of physical uniformities.
It is used in the determination of critical phenomena.
It helps in molecular weight determination.
It plays a vital role in the air pollution analysis
It gives an account of diffusion phenomena.
Why is the Clear Sky Blue? Why are the Clouds White?
The colour of the clear sky is blue because according to the Rayleigh scattering of light it can be clearly seen that as the light falls on the particles having a size smaller than the wavelength of light, the light gets scattered faster. As compared to other colours the blue colour oscillates faster because it has a shorter wavelength and higher frequency. That’s why the clear sky colour appears blue. The clouds are white due to Mie scattering. The cloud has water droplets and large particles in the atmosphere. So when the light having a smaller wavelength strikes these large particles, almost all the colours split equally and scatter in all directions. This gives the formation of white light. Hence, the clouds appear white.
NOTE: Rayleigh scattering is only for those particles having a smaller size than the wavelength of the incident light whereas Mie scattering is due to the larger size of the particles.
Exact Computational Methods
These types of methods are broadly classified into two types. These methods are the best approach to the scattering of light calculations. Let us discuss this in detail:
Finite-Difference Time-Domain Method (FDTD)
This method is generally used in grid-based differential time-domain numerical modelling methods. The finite differential equation is either solved by using software or hardware in a leapfrog manner.
T-matrix: (Null Field Method)
This technique is also known as EBCM (EXTENDED BOUNDARY TECHNIQUE METHOD). The solution through this method is done by matching boundary conditions by Maxwell equations. The incident transmitted and scattering fields are expanded into spherical vector wave functions.
Computational Approximation
The computational approximations of scattering light can be broadly classified into two major categories which are mentioned below:
Mie approximation
Discrete dipole approximation
The two types of approximation can be briefly described as:
Mie Approximation
This is a completely analytical-based solution of Maxwell's equation for the scattering of electromagnetic radiation by spherical particles. This has been formulated by Bohren and Huffman in the year of 1998. Taking into consideration of the arbitrary size parameter, the scattering from any spherical particles can be calculated using Mie theory. It is also called Lorenz- Mie theory or the Lorenz-Mie-Debye theory.
Discrete Dipole Approximation
The approximation of the continuous target by a finite array of polarisable points is termed as discrete dipole approximation. DDA courses are used to calculate DDA approximation in order to calculate light scattering particles.
Conclusion
This is all about the scattering of light and its different types. Find out the reasons behind various natural phenomena and the ways scattering of light is measured. Develop your concepts in this topic by concentrating on how the formulas are derived for measuring the scattering of light.
FAQs on Scattering of Light - Types, Explanation, Meaning, and FAQs
1. Who discovered light scattering? What are the benefits of scattering light?
The famous scientist CV Raman discovered the great phenomenon named light scattering in the year 1928 with the help of one of his students named K S Krishnan. in 1930 Raman was awarded a Nobel prize due to the discovery of Raman scattering. It helps in the analyzing of the tires of the particles which is very essential for the determination of so many criteria. The determination of the size of the particles helps in clear data production.
2. What happens if there is no scattering of light?
The vast number of exposure of colours in our atmosphere is due to the phenomenon known as the scattering of light. If there is no scattering of light then the sky looks blue because the oceans don't have colours. There will be no rainbow formation due to the lack of dispersion of light. The scattering of light plays a very vital role in nature. The sun would have looked white even during the times of sunrise and sunset.
3. Which colour is scattered the most?
The shortest the wavelength of colour, the more dispersed it will be. The blue colour of the atmosphere scatters the most when it enters the earth surrounding. This is because we can see the sky blue almost all the time. Due to its short wavelength, it is able to disperse in all directions.
4. Which light travels the fastest?
The red color travels the fastest in the atmosphere. This is because of its lesser refractive index that allows it to travel faster. The red colour travels in all mediums except the air. This is why this is the fastest as well as least dispersed light.
5. How light is scattered in the air?
Our atmosphere is a combination of smoke, dust, and many more granular particles. The ray of light, when passing through our earth's atmosphere, comes in contact with these particles which further leads to the dispersion of light in the atmosphere into the seven colours of rainbow during rainy days and follows the inverse proportionality process of wavelengths during normal days.