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. What is the scattering of light and why does it occur in the atmosphere?
Scattering of light is the process by which light rays deviate from their straight path when they interact with small particles or irregularities in a medium, such as air. It occurs in the atmosphere because dust, smoke, and gas molecules are always present, causing light to change direction and spread out in various ways. This phenomenon explains why we observe effects like the blue sky and colorful sunsets.
2. What are the main types of scattering of light studied in Physics?
The main types of light scattering are:
- Rayleigh Scattering: Occurs with particles much smaller than the wavelength of light; explains the blue color of the sky.
- Mie Scattering: Happens with particles comparable to or larger than the wavelength; responsible for the white appearance of clouds.
- Elastic and Inelastic Scattering: In elastic scattering (like Rayleigh and Mie), the wavelength of light does not change, while in inelastic scattering (like Raman and Compton), it does change.
3. Why does the clear sky appear blue while clouds look white?
The sky appears blue due to Rayleigh scattering, where particles smaller than the wavelength scatter shorter wavelengths (blue) much more effectively than longer ones. Clouds appear white because of Mie scattering from larger water droplets, which scatter all visible wavelengths almost equally, resulting in a white appearance.
4. How does the scattering of light explain the reddish color of the sky during sunrise and sunset?
During sunrise and sunset, sunlight travels a longer distance through the atmosphere. The shorter blue wavelengths are scattered away by the time the light reaches our eyes, leaving mainly the longer wavelengths like red and orange, which causes the sky to appear reddish near the horizon.
5. What factors determine the intensity and type of scattering experienced by light?
The intensity and type of light scattering depend on:
- Wavelength of the incident light: Shorter wavelengths scatter more strongly (inversely proportional to the fourth power of wavelength).
- Size of particles: Smaller particles favor Rayleigh scattering, while larger particles lead to Mie scattering.
- Nature of particles and medium: Shape, composition, and concentration of particles all play a role.
6. How does the concept of light scattering relate to real-world applications?
Light scattering has important applications, including:
- Explaining natural phenomena like blue skies, red sunsets, and the whiteness of clouds.
- Remote sensing and atmospheric studies.
- Medical diagnostics (such as analyzing tissues or blood).
- Environmental monitoring and air pollution analysis.
7. What is the difference between Rayleigh scattering and Mie scattering in terms of particle size and wavelength?
Rayleigh scattering occurs when the scattering particles are much smaller than the wavelength of light, leading to stronger scattering of shorter wavelengths (blue/violet). Mie scattering happens with larger particles, comparable to or greater than the wavelength, causing nearly equal scattering of all visible wavelengths, which explains the white color of clouds.
8. How are elastic and inelastic scattering processes different in Physics?
In elastic scattering, the energy (wavelength) of scattered light remains unchanged after interacting with particles (as in Rayleigh and Mie scattering). In inelastic scattering, the wavelength (and energy) of light changes due to energy transfer between light and the particles (examples include Raman and Compton scattering).
9. If there were no scattering of light in the atmosphere, how would our visual experience of the sky change?
Without scattering of light, the sky would not appear blue and would look dark, even during the day. Natural phenomena like the rainbow, colorful sunrises, and sunsets would not occur, and sunlight would pass through the atmosphere without changing direction or color.
10. How can the study of light scattering help in analyzing air pollution?
The study of light scattering helps detect and quantify particulate matter and pollutants in the atmosphere. By analyzing how light gets scattered by aerosols and dust, scientists can measure air quality and understand environmental changes.
