For this experiment let’s consider that we have an unpolarized light passing through two polarizer T1 and T2, here line on polarizer shows plane of vibration i.e., the plane in which electric field vector can vibrate freely, whereas electric field perpendicular to this line will be eliminated completely.

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Polarization by scattering is generally observed in liquid or gas randomness in motion of atoms. However, in perfect crystals we don’t see as good results as fluids.

For most people, a smelly bathroom is something to avoid. But when the ventilation stopped working in his lab’s hallway bathroom, indoor air expert Michael Link smelled opportunity.

Such a medium contains lots of atoms and when an unpolarized light beam strikes an atom it transfers energy to an atom. As a result, an electron in that atom starts vibrating in response to the electric component of the incident ray. Now, this vibrating electron emits E.M radiation in all directions, and this forces neighboring electrons to undergo a similar process. This phenomenon of absorption and emission of the electromagnetic radiation is known as the scattering of light.

Thus using Brewster’s law, we can conclude that polarizing angle depends on frequency of incident ray i.e., colour of incident ray hence polarizing angle will be different for different colour.

After analyzing their results collected over two weekends  — one with ventilation and one without — they found that the 222 nm UV light was producing enough ozone to react with chemicals in the air. The byproducts included formaldehyde, volatile organic compounds and nanoparticles.

And hence from this experiment we can conclude that electric fields are vibrating perpendicular to its direction of propagation, hence light is a transverse wave.

Link and Poppendieck wanted to know what those reactions looked like in the complex chemical soup of a real restroom. Their latest research, published in Environmental Science: Processes & Impacts, shows that these reactions produce pollutants that could be a health risk. As these sanitizers make their way into our homes and buildings, this research could help guide decisions on using them.

But this wavelength has its own unique drawback: It turns oxygen in the air into ozone. Ozone itself can be concerning, and it is also highly reactive with other chemicals in the air and creates new secondary compounds.  Link and Poppendieck wanted to know whether the new chemicals could pose a health risk.

Q: A sugar solution in a tube of length 2.0 dm produces optical rotation of 12°. Then, the sugar solution to one half of its initial concentration. If the dilute solute solution is contained in another tube of length 3.0 dm, the optical rotation produced by it will be

The specific rotation is a characteristic property of a certain substance and is the standard measurement for the optical rotation of that substance.

1. Linear polarization is when the oscillation of a wave is constrained to a single plane. This is the plane of polarization.

At the National Institute of Standards and Technology (NIST), Link and his colleague Dustin Poppendieck study air sanitizers that use ultraviolet light (UV). These devices kill pathogens such as those that cause the flu and COVID-19, but they can also cause unintended chemical reactions in the air.

When the electric field vectors are restricted to a single plane by filtration, then the light is said to be polarized with respect to the direction of propagation and it propagates in a single plane. In this article, we are going to learn about the polarization of light, brewster’s law, double refraction, polarization by scattering. Let’s understand the Physics (Optics) phenomenon of unpolarized light first.

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If the plane of vibration of both polarizers are parallel to each other in such polarized light from the first polarizer can easily pass through the second polarizer as shown below.

They decided to set up their study in a men’s restroom because it had urinal screens — those brightly colored pads placed over the drain to prevent splashing. These screens release fragrances (to mask the odor of urine) that include terpenes, a group of chemicals that reacts strongly with ozone. This study primarily focused on terpenes, but most bathrooms have air filled with chemicals such as cleaners and other scented hygiene products that would also react with ozone.

Light passing through a calcite crystal is split into two rays as shown below. This process is called double refraction or polarization by refraction.

For calcite, one of the two rays does indeed obey Snell’s Law (angle of incidence is equal to the angle of refraction), this ray is called the ordinary ray (or O-ray). The other ray (and any ray that does not obey Snell’s Law) is an extraordinary ray (or E-ray). For normal incidence (a Snell’s law angle of 0°), the two planes of polarization are also perpendicular to the plane of incidence.

UV air sanitizers were first widely used in the 1950s to combat tuberculosis. Those early attempts used UV with a wavelength of 254 nm, because that energy level is the most effective at breaking apart DNA and killing pathogens. It is still the most common type of UV air sanitation.

Polarization of Light is a property applying to transverse waves that specify the geometrical orientation of the oscillations. Light is an electromagnetic wave in which electric and magnetic field vectors are sinusoidally perpendicular to each other as well as they are perpendicular to the direction of propagation of light waves.

Substances are described as dextrorotatory or levorotatory according to whether the plane of polarization is rotated clockwise or counterclockwise, respectively, as determined by viewing towards the light source. Dextrorotation is designated (+) and levorotation is designated (-).

When the COVID-19 pandemic began, people started looking for effective ways to control airborne disease in indoor spaces. One promising approach was to use UV radiation. UV is light, but with a wavelength too short for our eyes to detect. Red light has a wavelength of about 700 nanometers (nm); yellow light, 580 nm; and ultraviolet light is between 400 and 100 nms. The shorter the wavelength, the higher the energy. UV light has enough energy to break apart DNA, which is why it’s effective at killing viruses in the air (and why you should wear sunscreen at the beach).

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This is the reason the sky scatters more blue light than red because of the natural frequency of molecules in our atmosphere.

Now if we rotate second polarizer in such a way that it becomes perpendicular to first one, in this case as plane polarized light passes through second polarizer it will get eliminated since second polarizer won’t allow it to pass and hence it is called analyzer which is used to determine the plane of polarization as shown below

Now as this unpolarized light passes through the polarizer, it will polarize the light in either vertical or horizontal direction. This polarized light when again passed through a polarizer there can be two possible outcomes.

Suppose if a pencil mark is drawn upon a sheet of paper and then covered with a piece of glass, only one image will be seen. But if the same paper is covered with a piece of calcite and the crystal is oriented in a specific direction then two marks will become visible. This is because a refracted beam acquires some degree of polarization. Most often, the polarization occurs in a plane perpendicular to the surface.

A polarimeter is an instrument used to determine the angle through which plane-polarized light has been rotated by a given sample.

Optical activity is the ability of a substance to rotate the plane of polarization of a beam of light that passed through it.

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The team installed 222 nm UV sanitizers in the bathroom along with a suite of chemical sensors. “I've never installed state-of-the-art air quality measuring devices in a bathroom,” said Link, first author on the study and patron of the laboratory lavatory. “We had to figure out how to get enough power into the bathroom for these instruments. We had to make sure we had a wireless internet connection so we could monitor our instruments in real time. We even had to consider things like not dropping electrical cords into the toilet.”

When we restrict vibration to an electrical vector in an unpolarized light we get plane polarized light. In this the direction of vibration of electric vector and direction of light propagation are perpendicular to each other as shown below.

Double refraction, also known as birefringence, is an optical property in which a single ray of unpolarized light entering an anisotropic medium is split into two rays i.e., ordinary & extraordinary rays, each traveling in a different direction.The concept of Double refraction can be observed by comparing two materials, glass and calcite.

In the carefully controlled environment of a lab, researchers can precisely measure air chemistry. But people don’t live in stainless steel lab chambers. “Standard lab tests only measure how ozone reacts with one or two pure chemicals,” Poppendieck explained. “In the real world, indoor air has tens if not hundreds of different chemicals that could potentially react in significant concentrations. Michael Link and I talked it over, and he suggested we run a real-world test to help us understand whether these lights are safe.”

Paper: Michael F. Link, Rileigh L. Robertson, Andrew Shore, Behrang H. Hamadani, Christina E. Cecelski and Dustin G. Poppendieck. Ozone generation and chemistry from 222 nm germicidal ultraviolet light in a fragrant restroom. Environmental Science: Processes & Impacts. Published online May 20, 2024. DOI: 10.1039/D4EM00144C

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The two rays of light are each plane-polarized by the calcite such that the planes of its polarization are mutually perpendicular to each other as shown below.

The velocity and refractive index of extraordinary waves changes with direction whereas for ordinary ray velocity remains constant throughout the crystal while propagating.

However the scattered light can be unpolarized, partially polarized, or completely polarized based on the direction of the incident ray as shown below.

The optical rotation is the angle through which the plane of polarization is rotated when polarized light is passed through a layer of a liquid.

3. Elliptical polarization is the same as circular polarization except that the amplitudes and phase differences are not the same.

UV light with a wavelength of 222 nm is still effective at killing pathogens, but the shorter wavelength doesn’t penetrate as deeply into human skin, so it’s safe to shine directly on people. Because of this, 222 nm UV light could be used to sanitize the air in small, crowded places like classrooms, elevators and public transportation, places where 254 nm UV sanitizers would be difficult to install easily.

But there’s a drawback to this high-energy UV; it can cause sunburn or temporary blindness. It has to be directed away from people, while still shining on the air they breathe. To use this UV safely, installers must position the lights carefully within ventilation shafts or point them toward the ceiling. This challenge of positioning UV sources is one of the main reasons this form of air purification isn’t used more widely. To avoid that risk, there has been a lot of interest in using less-damaging UV light.

So, as we discussed above, light is a transverse wave, and confining the plane of vibration of such a transverse wave by the principle of scattering is termed Polarization by scattering.

Ultimately these studies could be used to develop tests for UV air purifiers and guidelines for how to minimize their production of volatile chemicals. This information could ultimately guide decisions on how to best deploy UV sanitizers in a wide range of settings to optimize their benefits to human health.

When light wave propagates it consists of vibration of electric field in all possible direction, which are perpendicular to its direction of propagation and such light waves are said to be unpolarized light.

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Polarization due to scattering can be seen through the sky as we can see below. When an unpolarized beam of sunlight passes through the atmosphere the light scatters down towards earth. Also it has no vertical polarization.

There are three main types of polarization namely, linear polarization, circular polarization, and elliptical polarization.

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2. Circular polarization is when two linear components of a wave oscillate perpendicular to each other such that their amplitudes are equal.

NIST indoor air quality researchers closed a men’s restroom over two weekends to measure indoor air pollution caused by UV air sanitizers.

For monoclinic or tetragonal crystals, we get the above result i.e., One O-ray and one e-ray can be observed. Whereas for orthorhombic, monoclinic, and triclinic crystals, there will be two E-rays

We are sure that the above Physics (Optics) notes helped you to understand the importance of Polarization of Light. Get more study notes, practice sets, and puzzles, etc. on the Testbook App. Download the app now to avail exciting offers on select subscriptions!

To fully understand the importance of these chemical byproducts, researchers will need to conduct additional studies to determine how dangerous these pollutants might be, including on a wide variety of indoor spaces and environments that could benefit from the use of UV sanitizers. Other environments are expected to create different kinds of chemicals at different rates, and ventilation could affect how long they will stick around in the air.