What is polarisation by scattering Class 12?
2 Answers
Polarization by scattering refers to the process by which light waves become polarized due to scattering interactions with particles in the atmosphere or other media. When unpolarized light encounters small particles or molecules, it can scatter in various directions. However, the scattering intensity can vary with direction, leading to the alignment of the electric field vectors of the light waves.
### Key Points:
1. **Scattering Mechanism**: When light hits small particles, it can be scattered in different directions. The amount of scattering depends on the wavelength of the light and the size of the particles.
2. **Rayleigh Scattering**: This is a common type of scattering that occurs with particles much smaller than the wavelength of light. It explains why the sky appears blue; shorter wavelengths (blue light) are scattered more than longer wavelengths (red light).
3. **Polarization Effect**: The scattered light tends to be polarized. For example, when sunlight scatters off air molecules, the light that is scattered at 90 degrees to the direction of the incoming light becomes more polarized.
4. **Applications**: Polarization by scattering has practical applications, such as in photography (polarizing filters), in the study of atmospheric phenomena, and in understanding various optical properties of materials.
### Conclusion:
In summary, polarization by scattering is an important concept in optics that describes how light can become polarized when it interacts with particles. Understanding this phenomenon helps explain various natural phenomena and enhances techniques in fields like photography and atmospheric science.
### Key Points:
1. **Scattering Mechanism**: When light hits small particles, it can be scattered in different directions. The amount of scattering depends on the wavelength of the light and the size of the particles.
2. **Rayleigh Scattering**: This is a common type of scattering that occurs with particles much smaller than the wavelength of light. It explains why the sky appears blue; shorter wavelengths (blue light) are scattered more than longer wavelengths (red light).
3. **Polarization Effect**: The scattered light tends to be polarized. For example, when sunlight scatters off air molecules, the light that is scattered at 90 degrees to the direction of the incoming light becomes more polarized.
4. **Applications**: Polarization by scattering has practical applications, such as in photography (polarizing filters), in the study of atmospheric phenomena, and in understanding various optical properties of materials.
### Conclusion:
In summary, polarization by scattering is an important concept in optics that describes how light can become polarized when it interacts with particles. Understanding this phenomenon helps explain various natural phenomena and enhances techniques in fields like photography and atmospheric science.
### Polarization by Scattering
**Polarization by scattering** is a phenomenon in which light waves get polarized (i.e., their electric field oscillations become restricted to a particular direction) after interacting with particles in the atmosphere or other mediums.
This concept is often introduced in Class 12 physics in the context of wave optics and is crucial for understanding natural phenomena like why the sky appears blue and sunsets appear reddish.
### 1. **What is Polarization?**
Polarization refers to the orientation of the oscillations of the electric field in a light wave. Light waves are transverse waves, meaning their oscillations (both electric and magnetic fields) are perpendicular to the direction of wave propagation. Normally, light from most sources (like the Sun or a bulb) is **unpolarized**, meaning that the electric field oscillates in all possible directions perpendicular to the direction of travel.
In **polarized light**, the oscillations of the electric field are restricted to a specific direction.
### 2. **What is Scattering?**
Scattering occurs when light interacts with small particles (like dust, air molecules, or water droplets) in a medium, causing the light to deviate from its original direction. The interaction between the light and particles depends on the wavelength of the light and the size of the particles.
#### Example:
The atmosphere is filled with tiny air molecules. When sunlight passes through the atmosphere, the light interacts with these molecules and gets scattered in different directions.
### 3. **Polarization by Scattering Explained**
When sunlight enters the atmosphere, it interacts with air molecules and gets scattered. However, not all the scattered light remains unpolarized. At certain angles, especially at 90° to the incoming light, the scattered light becomes **linearly polarized**.
#### Why Does Polarization Happen?
- Sunlight is unpolarized, meaning that the electric field of light vibrates in all directions.
- When light encounters particles much smaller than its wavelength (like air molecules), the electrons in these molecules start oscillating in the direction of the electric field of the incoming light.
- These oscillating electrons then radiate light in all directions, but this scattered light is partially polarized, especially when observed at 90° from the direction of the incoming light.
Specifically:
- If you look at the sky 90° away from the direction of the Sun, the scattered light will be linearly polarized. This is because the scattered light in that direction has its electric field oscillations aligned in a specific direction, perpendicular to the direction of observation.
### 4. **Real-life Example: Blue Sky and Red Sunset**
- **Blue Sky:** Shorter wavelengths of light (like blue and violet) are scattered more efficiently by air molecules than longer wavelengths (like red). However, our eyes are more sensitive to blue light than violet light, so the sky appears blue. The scattered light from the blue sky is also polarized to some extent, which is why polarized sunglasses can reduce glare from the sky.
- **Red Sunset:** During sunset, sunlight has to travel through a thicker layer of the atmosphere. As a result, most of the shorter wavelengths (blue and violet) are scattered out, leaving the longer wavelengths (like red and orange) to dominate, giving the sky its reddish hue.
### 5. **Experimental Observation of Polarization by Scattering**
A simple experiment to observe polarization by scattering:
- Hold a polarizing filter (like polarized sunglasses) and look at the sky in a direction 90° away from the Sun.
- Rotate the filter. At certain angles, the sky will appear darker because the polarizing filter is blocking the polarized scattered light.
### 6. **Rayleigh Scattering and Polarization**
Polarization by scattering is closely related to **Rayleigh scattering**, which explains how light is scattered by particles much smaller than its wavelength. The degree of polarization of the scattered light depends on the scattering angle, with the maximum polarization occurring at 90° to the direction of the incoming light.
#### Rayleigh's Law:
The amount of scattering is inversely proportional to the fourth power of the wavelength:
\[ I \propto \frac{1}{\lambda^4} \]
This explains why shorter wavelengths (blue) are scattered more than longer wavelengths (red).
### Key Points to Remember:
- **Unpolarized Light**: Light waves have electric fields oscillating in all possible directions perpendicular to the direction of propagation.
- **Polarized Light**: The electric field oscillates in only one direction.
- **Scattering**: Interaction of light with particles, causing the light to spread out in different directions.
- **Polarization by Scattering**: The scattered light, especially at 90° to the original light path, becomes polarized due to interactions with particles in the atmosphere.
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This concept not only helps us understand why the sky is blue and sunsets are red, but it also has practical applications, such as in photography (using polarizing filters) and in studying atmospheric particles.
**Polarization by scattering** is a phenomenon in which light waves get polarized (i.e., their electric field oscillations become restricted to a particular direction) after interacting with particles in the atmosphere or other mediums.
This concept is often introduced in Class 12 physics in the context of wave optics and is crucial for understanding natural phenomena like why the sky appears blue and sunsets appear reddish.
### 1. **What is Polarization?**
Polarization refers to the orientation of the oscillations of the electric field in a light wave. Light waves are transverse waves, meaning their oscillations (both electric and magnetic fields) are perpendicular to the direction of wave propagation. Normally, light from most sources (like the Sun or a bulb) is **unpolarized**, meaning that the electric field oscillates in all possible directions perpendicular to the direction of travel.
In **polarized light**, the oscillations of the electric field are restricted to a specific direction.
### 2. **What is Scattering?**
Scattering occurs when light interacts with small particles (like dust, air molecules, or water droplets) in a medium, causing the light to deviate from its original direction. The interaction between the light and particles depends on the wavelength of the light and the size of the particles.
#### Example:
The atmosphere is filled with tiny air molecules. When sunlight passes through the atmosphere, the light interacts with these molecules and gets scattered in different directions.
### 3. **Polarization by Scattering Explained**
When sunlight enters the atmosphere, it interacts with air molecules and gets scattered. However, not all the scattered light remains unpolarized. At certain angles, especially at 90° to the incoming light, the scattered light becomes **linearly polarized**.
#### Why Does Polarization Happen?
- Sunlight is unpolarized, meaning that the electric field of light vibrates in all directions.
- When light encounters particles much smaller than its wavelength (like air molecules), the electrons in these molecules start oscillating in the direction of the electric field of the incoming light.
- These oscillating electrons then radiate light in all directions, but this scattered light is partially polarized, especially when observed at 90° from the direction of the incoming light.
Specifically:
- If you look at the sky 90° away from the direction of the Sun, the scattered light will be linearly polarized. This is because the scattered light in that direction has its electric field oscillations aligned in a specific direction, perpendicular to the direction of observation.
### 4. **Real-life Example: Blue Sky and Red Sunset**
- **Blue Sky:** Shorter wavelengths of light (like blue and violet) are scattered more efficiently by air molecules than longer wavelengths (like red). However, our eyes are more sensitive to blue light than violet light, so the sky appears blue. The scattered light from the blue sky is also polarized to some extent, which is why polarized sunglasses can reduce glare from the sky.
- **Red Sunset:** During sunset, sunlight has to travel through a thicker layer of the atmosphere. As a result, most of the shorter wavelengths (blue and violet) are scattered out, leaving the longer wavelengths (like red and orange) to dominate, giving the sky its reddish hue.
### 5. **Experimental Observation of Polarization by Scattering**
A simple experiment to observe polarization by scattering:
- Hold a polarizing filter (like polarized sunglasses) and look at the sky in a direction 90° away from the Sun.
- Rotate the filter. At certain angles, the sky will appear darker because the polarizing filter is blocking the polarized scattered light.
### 6. **Rayleigh Scattering and Polarization**
Polarization by scattering is closely related to **Rayleigh scattering**, which explains how light is scattered by particles much smaller than its wavelength. The degree of polarization of the scattered light depends on the scattering angle, with the maximum polarization occurring at 90° to the direction of the incoming light.
#### Rayleigh's Law:
The amount of scattering is inversely proportional to the fourth power of the wavelength:
\[ I \propto \frac{1}{\lambda^4} \]
This explains why shorter wavelengths (blue) are scattered more than longer wavelengths (red).
### Key Points to Remember:
- **Unpolarized Light**: Light waves have electric fields oscillating in all possible directions perpendicular to the direction of propagation.
- **Polarized Light**: The electric field oscillates in only one direction.
- **Scattering**: Interaction of light with particles, causing the light to spread out in different directions.
- **Polarization by Scattering**: The scattered light, especially at 90° to the original light path, becomes polarized due to interactions with particles in the atmosphere.
---
This concept not only helps us understand why the sky is blue and sunsets are red, but it also has practical applications, such as in photography (using polarizing filters) and in studying atmospheric particles.