Table of Contents
Introduction:
Polarisation in physics is a feature of certain electromagnetic radiations in which the vibrating electric field’s direction and magnitude are associated in a specific way.
The vibrating electric vector associated with each wave is perpendicular to the propagation direction, making light waves transverse. Waves traveling in the same direction with their electric vectors pointing in random directions around the propagation axis make up an unpolarized light beam. Plane polarised light is made up of waves with the same direction of vibration for all of them.
As the wave propagates, the electric vector rotates around the propagation direction in circular polarisation. Light can be polarised through reflection or traveling through filters, such as crystals, that transmit vibration in one plane but not in others.
Understanding: Polarisation in Physics
Light is an electromagnetic wave with an electric field that oscillates perpendicular to the wave’s propagation path. If the direction of this electric field varies randomly over time, light is said to be unpolarized. Unpolarized light is produced by many common light sources, including sunshine, halogen illumination, LED spotlights, and incandescent bulbs. Polarised light is described as light with a well-defined direction of the electric field. A laser is the most common generator of polarised light.
We divide polarised light into three categories based on the orientation of the electric field:
Linear Polarisation: Along the propagation direction, the electric field of light is restricted to a single plane.
Circular polarization: The electric field of light is made up of two perpendicular linear components that are identical in amplitude but have a phase difference of 2. The resulting electric field spins in a circle around the propagation direction and is referred to as left- or right-hand circularly polarised light depending on the rotation direction.
Elliptical polarization: It describes an ellipse in the electric field of light. This occurs when two linear components with different amplitudes and/or a phase difference that is not /2 are combined. Circular and linear polarised light are particular examples of elliptically polarised light, which is the most general description of polarised light.
Polarisation of lights
The process of polarisation is the transformation of non-polarized light into polarised light. Unpolarised light is defined as light in which particles vibrate in all planes.
A light wave that vibrates in more than one plane is known as unpolarised light. The light released by the sun, a lamp, and a tube light are all examples of unpolarized light sources.
A polarised wave is the polarised version of a wave. Polarised waves are light waves that vibrate in a single plane. Plane polarised light is made up of waves that all vibrate in the same direction.
Two Types of wave are involved in Polarisation
Transverse Wave: The waves in which the particles move in a perpendicular direction to the wave’s motion direction. When you throw a stone, for example, it causes ripples in the water and sound waves to travel through the air.
Longitudinal Wave: The particle displacement in a longitudinal wave is parallel to the wave propagation direction.
Light is a combination of electric and magnetic forces traveling across space. The electric and magnetic vibrations of a light wave are perpendicular to each other. The magnetic field is always perpendicular to the electric field, which travels in the opposite direction. So we have an electric field in one plane, a magnetic field perpendicular to it, and a perpendicular travel direction. Vibrations of electric and magnetic fields can occur in a variety of planes.
Examples of polarisation of light in daily life
Identification of Chemicals
In the chemical, pharmaceutical, and food and beverage sectors, polarisation control is also critical. There are numerous orientations in many important organic chemical molecules, such as active medicinal components and sugars. Stereochemistry is the study of molecules with various orientations.
Stereoisomers are chemical compounds with the same type and number of atoms but different molecular configurations. These stereoisomers are “optically active,” which means they can rotate polarised light in various directions. Polarimetry can detect and quantify the quantity of these substances since the amount of rotation is determined by the nature and concentration of the compound. This is the foundation for determining which stereoisomer is present in a sample, which is crucial because stereoisomers can have drastically different chemical effects. The stereoisomer limonene, for example, is the molecule that gives oranges and lemons their distinct fragrances.
Microscopy of Polarisation
Polarisers are used in a range of microscopy techniques, including differential interference contrast (DIC) microscopy, to generate a variety of effects.
A linear polariser is positioned in front of a microscope light source, below the specimen stage, in a simple polarisation microscope system to polarise the light entering the system. An “analyzer” is a second linear polariser placed above the specimen stage that is rotated to provide the desired effect when analysing the sample while the first polariser remains stationary.
The analyzer is then rotated so that the analyzer and polariser polarisation planes are 90 degrees apart. The microscope will have a minimal transmission (crossed polarizers) after this is accomplished; the amount of light transmission will be proportional to the extinction ratio of the polarizer and analyzer.
An anisotropic, or birefringent, the specimen is put on the specimen stage after the analyzer has been positioned perpendicularly to the polariser. Before the polarised light reaches the analyzer, the specimen rotates it a certain amount, according to the specimen thickness (and hence the optical path distance) and the specimen birefringence.
Also read: Important Topic Of Physics: Plane Polarized Light
Frequently Asked Questions FAQs
Does polarisation have an effect on the intensity of light?
Although light intensity remains constant regardless of polarisation, when unpolarized light, such as sunshine or ordinary light bulb light, is delivered through a polarizer, only half of the intensity passes through since the other half is blocked.
What is the mechanism through which polarisation reduces glare?
Polarized lenses use a chemical layer that is either applied to or integrated into the lenses to reduce glare. Polarized sunglasses have a chemical filter that reduces glare by absorbing horizontal light while allowing vertical light to pass through. Glare is mainly reflected horizontal light that we perceive as glare.
Why is polarised light scattered?
Light is linearly polarised in the plane perpendicular to the incident light when it scatters off air molecules. If a molecule's charges oscillate along the y-axis, the molecule will not radiate along the y-axis. As a result, the dispersed light is linearly polarised when it is 90 degrees away from the beam path.
