ultraviolet rays definition
Ultraviolet radiation is an electromagnetic wave whose wavelength is shorter than visible light, but longer than x-rays. It is called ultraviolet because the wavelength of violet is the shortest among the colors of the spectrum. Its wavelength ranges from 400 nm to 10 nm and its energy from 3 eV to 124 eV. Ultraviolet rays are sometimes called black rays because they are not visible to the naked eye and are usually symbolized by the first two letters of their name, u.v. It has several applications in medicine, lighting and chemistry.
Ultraviolet rays are found in sunlight and are emitted by an electric arc or black light. Because this is ionizing radiation, it can cause a chemical reaction, causing many materials to glow or fluoresce. Many people have realized the effect of ultraviolet rays on the body, causing heatstroke, but the spectrum of these rays has other effects that can be beneficial or harmful to human health.
The discovery of ultraviolet rays
The man credited with discovering ultraviolet rays is German physicist Johann Ritter, who lived between 1776 and 1910. Ritter experimented with silver chloride, a chemical known to decompose when exposed in the sun, and found that light at the blue tip of the visible spectrum (blue, indigo, and violet) was a more effective catalyst for this reaction.
After another experiment, Ritter found that silver chloride collapsed more effectively when exposed to radiation behind the blue color of the visible spectrum, and described this new type of radiation as ultraviolet, that is- ie beyond purple.
ultraviolet rays meaning
The first step is to answer the question « What is UV? »Define the components of the question itself; Where « rays » are defined as energy that propagates through time, and the word « ultraviolet » means beyond violet, where German physicist Johann Wilhelm Ritter discovered ultraviolet in 1801 AD, when he noticed the presence of invisible light beyond the purple part of visible light on silver chloride treated paper, faster than violet light in the visible spectrum, and called invisible light « oxidizing rays » for indicate the chemical activity of the radiation and to distinguish it from « heat rays » discovered the previous year at the other end of the visible spectrum some time later Short A simpler term « chemical rays » was adopted and remained popular throughout the 19th century, until the first terms were finally abandoned in favor of « ultraviolet » and « infrared », respectively.
So the question « What is ultraviolet radiation? » Can be answered. It is a region of the electromagnetic spectrum that lies between visible light and x-rays and is invisible to the human eye; Because it has a shorter wavelength and a higher frequency than the light the human brain perceives in the form of images, and by studying the question « What is ultraviolet radiation? We find that the sun is the greatest source of ultraviolet rays, with ultraviolet rays occupying about 10% of total sunlight, and some lasers can produce ultraviolet rays, and insect stun, which attracts insects that can seeing ultraviolet rays is one example. devices that emit ultraviolet rays, and ultraviolet rays are generally divided into three sub-bands as follows :
- UVA or near ultraviolet rays: this type has the longest wavelength and is considered the least harmful. It can be known as « black light » and many use its ability to glow in artistic and festive designs.
- UVB: Usually the most destructive form of UV light because it contains enough energy to damage cellular DNA.
- UVC or far ultraviolet rays: This type is very harmful and is almost completely absorbed by the Earth’s atmosphere.
And there are extreme ultraviolet rays that the Earth’s atmosphere prevents from reaching Earth and staying in space, where sunlight is made up of about 50% infrared radiation, 40% visible light, and 10%. % ultraviolet rays, but The ozone layer in Earth’s atmosphere absorbs high energy and harmful levels of ultraviolet rays, such as far and middle ultraviolet rays, the scientists found when answering « What ultraviolet rays? Ozone absorbs about 95% of far ultraviolet rays, but these harmful rays can penetrate the ozone layer.
ultraviolet rays wavelength
Wavelength: The wavelengths of ultraviolet rays range from 10 nanometers to 400 nanometers, and their distribution is as follows : Rayonnement proche ultraviolet :
- Near ultraviolet radiation : It has wavelengths from 315 to 400 nanometers.
- Average UV : It has wavelengths from 280 to 315 nanometers.
- Far ultraviolet rays : They have wavelengths from 180 to 280 nanometers.
- Extreme UV rays : They have wavelengths from 10 to 180 nanometers.
Properties of UV ultraviolet rays
This is clear from the answer to the question « What is ultraviolet radiation? » These are waves that belong to the electromagnetic spectrum, so they, like waves, have unique wave properties that give them many advantages, which in turn is also the reason why ultraviolet rays are dangerous in many ways, and these properties are as follows :
- Frequency: Ultraviolet rays have higher frequencies than visible light, with frequencies between 10 ^ 15 and 17 ^ 10 Hz.
- Wavelength: The wavelengths of ultraviolet rays range from 10 nanometers to 400 nanometers.
- Energy: The energy carried by UV rays varies from 3 MeV to 124 MeV.
ultraviolet rays examples
- UVA : has a wavelength of 320 to 400 nm. Although their energy is lower than that of UVB, they penetrate the dermis and are responsible for immediate tanning, premature aging of the skin and may play a role in the development of certain skin cancers. UVA rays are not easily absorbed by the ozone layer; about 95% succeed in crossing it.
- UVB rays : have a wavelength of 280-320 nm. They only penetrate the protective layer of the epidermis. They are responsible for long-term tanning and sunburn, as well as most skin cancers. A large part of UVB is absorbed by the ozone layer; only 5% make it to the surface of the earth.
- UVC : has a wavelength of 100 to 280 nm and is the UV rays with the most energy. They are very dangerous for all forms of life (even at very low doses). On the other hand, they do not cross the ozone layer and never reach the earth. They are artificially created to kill bacteria.
ultraviolet rays application
- In lighting, the existence of « fluorescent » tubes, where the ultraviolet radiation emitted by an electric discharge in a gas is used to excite the fluorescence spectrum (visible) of the deposit covering the wall of the tube. The color temperature is higher, the actual temperature lower, and the visible light output (20 percent of the energy expended) better than in incandescent lighting.
- In graphic reproduction techniques (drawing of plans, etc.).
- In microscopy, by the gain in resolving power resulting from the reduction of the diffraction spot (the size of which is proportional to the wavelength).
- For the production of ozone (cf. oxygen).
- In fluorescence applications for viewing fixed or moving objects: the sources are fitted with a filter such as a nickel glass, stopping visible light: this is Wood’s light, or black light .
- In spectrochemical analysis by emission. This method, using the spectrum emitted by arcs or sparks in the visible and the ultraviolet, is very widely used in laboratories and in industry (in the steel industry, for example), and network devices equipped with multiple Exit slits and photoelectric receivers (quantometers) allow simultaneous determination of the concentrations of a large number of elements in the sample. The field of application of this method extends to the beginning of the far ultraviolet, where there are sensitive lines of non-metallic elements. One possibility of extending it to all metalloids consists of using a vacuum spark, a more powerful source which excites the ion spectra of these elements.
Damage caused by ultraviolet rays
Exposure to the sun’s ultraviolet rays causes a lot of damage to the skin, such as sunburn and melasma, and there are more serious damage that does not happen once but takes years to appear, such as that skin cancer, cataracts, premature aging and the appearance of wrinkles, and the solution is to avoid exposure to the above sunrays and take precautions that reduce its effect, and we l ‘explain in simple steps you can take to protect yourself.
How to Avoid UV Damage
- Choosing the right sunscreen
- Wear sunglasses
- stand in the shade
- Avoid going out during rush hour