# Polarisation of Light: Causes & Effects

• Cheman
In summary, light can be polarized when the electric field vector is oriented in a specific direction. This can occur due to the motion of electrons, which can produce linearly, circularly, or unpolarized light depending on the type of motion. Magnetic fields are also a common source of circularly polarized light.
Cheman
Polarisation of light...

With light, the elctric and magnetic fields are perpendicular to the direction of wave travel - but my textbook says that these also exist in every plane, forming almost like a cylinder. This is what means it can be polarised. But what causes this? ie - what are the electrons doing to cause the elctric field to be in all directions?

Further more, what happens to the magnetic fields when light is polarised - does this remain perpendicular to the elctric field remaining?

The electric and magnetic fields are always at right angles to each other in an electromagnetic wave. By convention, the direction of polarisation of the light is taken to be the direction of the electric field vector.

At a single point in space, the electric field vector can only point in one direction at a time. If it maintains the same orientation along the wave, the wave is plane polarised. If the field vector rotates along the wave, then the wave is circularly (or elliptically) polarised.

Light may also be unpolarised. Unpolarised light is the sum of many polarised waves, randomly oriented. Unpolarised light is characterised by the fact that when one decomposes the field into two orthogonal polarisations, the components are always equal. In practical terms, this means that only 50% of light will go through a polaroid, no matter the orientation of the polaroid.

Claude.

Cheman said:
This is what means it can be polarised. But what causes this? ie - what are the electrons doing to cause the elctric field to be in all directions?

The type of polarization depends on how the electron is moving perpendicular to your line of sight. Motion toward or away from you will not induce an electromagnetic wave, but tangential motion will. If the electron is oscillating back and forth in a line, the light will be linearly polarized. If it's spinning in a circle, then it will give circularly polarized light. Finally, if there are many electrons and they're all moving in random directions, then the result will be unpolarized light.

Direct light from the sun, for example, is unpolarized because its emission is coming from charges undergoing random thermal motion in the photosphere. On the other hand, scattered light from around the sun will be linearly polarized because the scatterers will be oscillating in a plane perpendicular to the line of sight. Finally, magnetic fields are a common source of circularly polarized light.

## What is polarisation of light?

Polarisation of light is a phenomenon that occurs when light waves vibrate in a single plane. This means that all the light waves are aligned in one direction, rather than vibrating in all directions.

## What causes polarisation of light?

Polarisation of light can be caused by various factors, such as reflection, refraction, scattering, and transmission through certain materials. These processes can align the light waves in a single plane, resulting in polarised light.

## What are the effects of polarisation of light?

The effects of polarisation of light can be observed in various ways. For example, polarised light can reduce glare and improve contrast, making it useful for sunglasses and 3D glasses. It can also affect the way light is reflected and transmitted through certain materials, which has practical applications in photography and telecommunications.

## How is polarisation of light measured?

Polarisation of light is typically measured using a polarimeter, which consists of a light source, a polariser, and an analyser. The polariser filters the light waves, allowing only polarised light to pass through. The analyser then measures the intensity of the polarised light, which can be used to determine the degree of polarisation.

## What are some real-life applications of polarisation of light?

Polarisation of light has many practical applications in various industries. For example, polarised light is used in photography to reduce glare and improve image quality. It is also used in LCD screens and 3D glasses to control the direction of light and create images. In addition, polarised light is used in telecommunications to transmit signals more efficiently and in material testing to detect stress and strain in objects.

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