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Ultraviolet light is a type of electromagnetic radiation
UV light comes from the sun and is transmitted in waves or particles at different wavelengths an frequencies.
It makes black-light posters glow, and is responsible for summer tans. But too much exposure to UV radiation damage living tissue.
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The electromagnetic (EM) spectrum
EM is the broad range of wavelengths. It is divided into seven regions and ordered in decreasing wavelength and increasing energy and frequency, namely radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays.
Ultraviolet light falls is the range of the EM spectrum between visible light and X-rays.
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UV is generally divided into three sub-bands
- UVA, or near UV (315-400 nanometers)
- UVB, or middle UV (280-315 nanometers)
- UVC, or far UV (180-280 nanometers)
Radiations with wavelengths from 10nm to 180nm are sometimes referred to as vacuum or extreme UV.
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Ionization
UV radiation has enough energy to break chemical bonds. UV photons can cause ionization, meaning chemical bonds will break that otherwise would not.
It can be useful, for instance, in disinfecting a surface, but it can also damage materials and living tissues, particularly the skin and eyes that are affected by UVB and UVC radiation.
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UV effects
Most natural UV light comes from the sun. Only 10 % of sunlight is UV, and only one-third of it gets through the atmosphere.
Of the solar UV energy that reaches the equator, 95% is UVA, and 5% is UVB. No measurable UVC from the sun gets to the Earth's surface, because ozone, molecular oxygen, and water vapour in the upper atmosphere absorb the shortest UV wavelengths.
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UV radiation and sunburn
A suntan is a reaction to exposure to UVB rays. When the body senses sun damage, it sends melanin, a pigment in the body, to absorb UV light and protect the body from more damage, resulting in a darkened skin.
Continued exposure to UV radiation can damage the body's DNA. When the body senses this destruction, it floods the area with blood and inflammation to help with the healing process. Sometimes the cells with DNA mutated by the sun's rays turn into problem cells, known as skin cancer.
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Fluorescence
Substances like minerals, plants, fungi, microbes, and organic and inorganic chemicals, can absorb UV radiation, causing electrons to jump to a higher energy level. When the electrons return to a lower energy level, they emit a portion of the absorbed energy as visible light.
- Fluorescence is used for signs, safety vests, and other applications in which high visibility is important.
- In fluorescent tubes, an electric current is passed through mercury vapour, producing ultraviolet radiation along with a blue light.
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UV astronomy
There are also other celestial sources of UV radiation.
Very large young stars shine most of their light in ultraviolet wavelengths. But the Earth's atmosphere blocks much of the UV radiation, and observations are conducted using high-altitude balloons and special orbiting telescopes equipped to observe the UV region of the EM spectrum.
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UV light as a cancer treatment
Some skin conditions can be treated using UV light.
PUVA (psoralen ultraviolet light treatment) is used to treat lymphoma, eczema, psoriasis, and vitiligo. Patients take a drug or apply a lotion to make their skin sensitive to light. Then a UV light is shone on the skin, slowing down the growth of the skin cells.
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The Calculations Of Light
- The colour-sensitive receptors that humans have, called melanopsin, measure the amount of blue or yellow light in the atmosphere and likewise regulate our circadian rhythm.
- Human beings have Cone Cells, which are of three types, Red, Blue, and Green, and have evolved much later than the receptors in the brain.
Colour Is A Private Sensation
- Research proves that the universal emotional responses that we have when we see a colour tend to be the same, even if the actual colour is different, as our conscious perception of those colours varies.
- The day-night cycle of living things is impacted by the ambient light, where the morning yellow light awakens us or makes us feel happy, and the dominance of blue light at night makes us feel sleepy.
Misophonia
Misophonia is characterized by strong negative emotions such as anger and anxiety in response to everyday sounds other people make. These sounds include humming, chewing, t...
Misophonia and brain particularities
Scientists do not fully understand misophonia but suspect it's caused by the way some people's brains process particular sounds and react to them.
Some studies found that the brains of people with misophonia showed hyperactivation of the salience network, a group of brain areas that direct our attention to important things in our surroundings. Trigger sounds send the salience network into an overdrive. Researchers found these brain areas are structurally more robust in people with misophonia.
Calming a misophonic brain
There's a lot of similarity between people who experience misophonia, but also a lot of diversity.
Therapists use a variety of techniques that is often based on the symptoms. Those who experience fear and anxiety may respond to exposure-based treatments. Those who experience anger can learn to manage their distress through distraction or relaxation techniques.
The history of refrigeration
Refrigeration is the action of creating cooling conditions by removing heat. It is used for preserving food by slowing bacteria growth.
- Around 1000BC, the Chinese u...
Evaporative cooling
- 1720s. Scottish doctor William Cullen saw that evaporation had a cooling effect.
- 1748. Cullen demonstrated his ideas by evaporating ethyl ether in a vacuum.
- 1805. Oliver Evans designed a refrigeration machine that used vapor instead of liquid.
- 1820. English scientist Micahel Faraday used liquefied ammonia for cooling.
- 1835. Jacob Perkins, who worked with Evans, patented a vapor-compression cycle using liquid ammonia.
- 1842. John Gorrie, an American doctor, built a machine similar to Evans's design to artificially create ice and cool down patients with yellow fever.
- New and improved refrigeration ideas continued to be developed, including Albert Einstein's idea of an environmentally friendly refrigerator with no moving parts that did not rely on electricity.
- By 1920, refrigerators were considered essential in American homes.
How refrigerators work
Refrigerators today work by evaporating liquids.
The liquids are pushed through the refrigerator through tubes and begin to vaporize. As the liquids evaporate, they carry heat away with them as the gases travel to a coil outside the refrigerator. Here the heat is released. The gases return to a compressor, where they become liquid again, restarting the cycle.