what is the prinicple of uv-vis?
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The UV-VIS spectrum is due to the electronic transitions of the molecule. This is characteristic of a compound. Qualitative and quantitative estimations of compounds are possible by this non destructive technique. \n\nThe absorption (A) of a solution at a particular wavelength is given by Beer-Lambert's law ect = A where c is the concentration of the compound , t is the thickness of the cell and e is the molar extinction coefficient characteristic of the compound at a given wavelength. This principle is used for quantitative measurements. \n\nCary 5E is a high resolution spectrophotometer to study the electronic spectrum of solutions, single crystals and powder samples (in nujol mull) in the range of 3150-185 nm. This is a double beam instrument controlled by a microprocessor. Base line correction, repetitive scan, kinetics, derivative and concentration modes are possible. Diffuse reflectance is available for solid samples. VT accessory in the range 5-90 degrees Centigrade is available\n\nThis principle is used for quantitative measurements.
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It's not totally unaltered:\n\nThe most obvious characteristic of ordinary glass is that it is transparent to visible light (not all glassy materials are). This transparency is due to an absence of electronic transition states in the range of visible light, and because ordinary glass is homogeneous on all length scales greater than about a wavelength of visible light. (Heterogeneities cause light to be scattered, breaking up any coherent image transmission). Ordinary glass partially blocks UVA (wavelength between 400 and 300 nm) and totally blocks UVC and UVB (wavelengths shorter than 300 nm) due to the addition of compounds such as soda ash (sodium carbonate).
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I would guess that if you took a UV spectrum of ascorbic acid, you would find the maximum absorbance at 254 nm. Therefore, the most accurate analysis of the eluent would be looking at that wavelength.
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There's not UV filtering, no ozone layer to protect it.  It will be burned by UV radiation.
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UV Index – a measure of the intensity of the sun’s ultraviolet radiation in the sunburning spectrum (290 to 400 nm). As the UV Index increases, the sun’s rays can do more harm to your skin, eyes and immune system and one should therefore take more precautions to protect yourself from the harmful rays. In Canada, the UV Index ranges from 0 – 10. 0 – 4 is low, 4 to 7 is moderate, 7 – 9 is high, and over 9 is extreme. \n\nFor information on how the UV Index is calculated in the U.S. click on this link - http://www.epa.gov/sunwise/uvcalc.html
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actually it should be. bronzing rays (UVA) go deeper into your skin to hold color longer and better. they also take away the red tint that you might posess when you are tanning. and they are usually not as hot temperature wise!
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Violet (about 400 nm) [for visible light (380 THz to 750 THz)]
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According to their website, they are using a narrow band UVB process. They state:\n\n"Narrow Band UVB virtually eliminates superfluous and harmful UV by emitting only wavelengths 311-312 nm. Clinical studies show the peak therapeutic effectiveness of UVB to be within the range of 295-313 nm, but wavelengths below 300 nm can cause erythema or severe burning and increase the risk of skin cancer. "\n\nHope this sets you mind at ease!
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Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays\nThe conventional black light(UV Rays are called Black light) design is just a fluorescent lamp with a couple of important modifications. Fluorescent lamps generate light by passing electricity through a tube filled with inert gas and a small amount of mercury. \nThe first thing most people notice when you switch on a black light is that some of their clothing glows. This is because most laundry detergents contain phosphors to make whites appear brighter in sunlight. Sunlight contains UV light that makes the whites glow "brighter than white." Dark clothes don't glow because the dark pigments absorb the UV light.\nThere are a lot of everyday materials that fluoresce, or glow, when placed under a black light. A black light gives off highly energetic ultraviolet light. You can't see this part of the spectrum, which is how 'black lights' got their name. Fluorescent substances absorb the ultraviolet light and then re-emit it almost instantaneously. Some energy gets lost in the process, so the emitted light has a longer wavelength than the absorbed radiation, which makes this light visible and causes the material to appear to 'glow'. \nFluorescent molecules tend to have rigid structures and delocalized electrons. Examples of common materials that contain fluorescent molecules include: \n\nWhite paper is treated with fluorescent compounds to help it appear brighter and therefore whiter. \n\n some other things to glow under UV light are\nClub Soda or Tonic Water\nThe bitter flavoring of tonic water is due to the presence of quinine, which glows blue-white when placed under a black light. \n\nBody Fluids\nMany body fluids contain fluorescent molecules. Forensic scientists use ultraviolet lights at crime scenes to find blood, urine, or semen (all fluorescent).\n\nVitamins\nVitamin A and the B vitamins thiamine, niacin, and riboflavin are strongly fluorescent. Try crushing a vitamin B-12 tablet and dissolving it in vinegar. The solution will glow bright yellow under under a black light.\n\nChlorophyll\nChlorophyll makes plants green, but it fluoresces a blood red color. Grind some spinach or swiss chard in a small amount of alcohol (e.g., vodka or everclear) and pour it through a coffee filter to get chlorophyll extract (you keep the part that stays on the filter, not the liquid). You can see the red glow using a black light or even a strong fluorescent bulb, such as an overhead projector lamp, which (you guessed it) gives off ultraviolet light.\n\nAntifreeze\nManufacturers purposedly include fluorescent additives in antifreeze fluid so that black lights can be used to find antifreeze splashes to help invesitagors reconstruct automobile accident scenes.\n\nLaundry Detergents\nSome of the whiteners in detergent work by making your clothing a bit fluorescent. Even though clothing is rinsed after washing, residues on white clothing cause it to glow bluish-white under a black light. Blueing agents and softening agents often contain fluorescent dyes, too. The presence of these molecules sometimes causes white clothing to appear blue in photographs.\n\nTooth Whiteners\nWhiteners and some enamels contain compounds that glow blue to keep teeth from appearing yellow.\n\nPostage Stamps\nStamps are printed with inks that contain fluorescent dyes.\n\nJellyfish\nIf you have a jellyfish handy, see what it looks like under a black light in a darkened room. Some of the proteins within a jellyfish are intensely fluorescent.\n\nSome Minerals and Gems\nFluorescent rocks include fluorite, calcite, gypsum, ruby, talc, opal, agate, quartz, and amber. Minerals and gemstones are most commonly made fluorescent or phosphorescent due to the presence of impurities. The Hope Diamond, which is blue, phosphoresces red for several seconds after exposure to shortwave ultraviolet light.
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The so called ultraviolet catastrophe of the Rayleigh-Jeans law of black body radiation.\n\nhttp://en.wikipedia.org/wiki/Rayleigh-Jeans_law\n\n------------\n\nA similar question\nhttp://answers.yahoo.com/question/index;_ylt=AiSEt83vSVIv92vc9vsdCtzsy6IX?qid=1006022704468
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UV invisible ink is made using a volatile application base, and mixed into it is a compound that is transparent to visable wavelengths of light but not UV. When you shine UV light on it, the compound fluoresces and the wavelength of the light is increased during thing process therefore allowing you so see the bright blueish/purpleish mark of the ink.
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No polarization does not offer UV protection as far as I've been able to find out.  UV protection has to be added to the lens in addition to having them polarized.
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In the US, the UV Index is computed using forecasted ozone levels, a computer model that relates ozone levels to UV incidence (incoming radiation level) on the ground, forecasted cloud amounts, and the elevation of the forecast cities. Certain other countries also use ground observations.\n\nThe calculation starts with measurements of current total ozone amounts for the entire globe, obtained via two satellites operated by the National Oceanic and Atmospheric Administration (NOAA). These data are then used to produce a forecast of ozone levels for the next day at various points around the country. A model is then used to determine the amount of UV radiation reaching the ground from 290 to 400 nm in wavelength (representing the full spectrum of UV wavelengths), using the time of day (solar noon), day of year, and latitude. As an example, assume the following UV levels for each wavelength are predicted for a given location (these are totally made up numbers, and not even the ratios represent reality):
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UVA:\nCan pass through window glass.\nIs not affected by a change in altitude or weather.\nIs present all day and every day of the year.\nPenetrates deep into skin layers.\nIs 5% of the sun's rays.\nIs 20 times more abundant than UVB rays.\nAffects long-term skin damage.\n\nUVB:\nCannot pass through window glass.\nCauses sunburn.\nCauses tanning.\nHelps the body with normal vitamin D production.\nVaries with the season. It is more intense in the summer than in the winter.\nVaries with weather conditions.\nIs more intense at midday than in the morning or late afternoon.\nIs more intense at high altitudes and near the equator.\nIs 0.5% of the sun's rays.\nIs protected against by the sun protection factor (SPF) in sunscreens.\nIs related to more than 90% of nonmelanoma skin cancer.\nIs related to cataracts.\n\nMore:\n\nHow Sunlight Works\n\nSunlight arrives on earth in three forms: infrared (heat), visible light and ultraviolet. Ultraviolet light is classified into three categories: \nUVA (315 to 400 nm), also known as black light, which causes tanning \nUVB (280 to 315 nm), which causes damage in the form of sunburn \nUVC (100 to 280 nm), which is filtered out by the atmosphere and never reaches us. \n99% of the sun's UV radiation at sea level is UVA. It is the UVB that causes most of the problems related to sun exposure: things like aging, wrinkles, cancer and so on, although research is increasingly implicating UVA as well. \nOne of the interesting things about UV radiation is that it is reflected by different surfaces. These reflections can amplify the effects of UV exposure. For example, snow reflects 90% of UV light. That is why you can get snow blindness and severe sunburns from skiing on a sunny day. Sand can reflect up to 20% of UVB that hits it, meaning that you can get extra UV exposure at the beach. \n\nOn the other hand, certain things absorb almost all UV radiation partially or completely. Glass is one of these substances - many glasses are very good absorbers of UV (which is why you may have heard that you cannot get sunburn in a greenhouse - just make sure it is glass and not plastic covering the greenhouse!). Most sunscreens use chemicals that have the same UV-absorbing properties.
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try looking for a script here to do that\nhttp://web-master.uv.ro\nor try to it's partners
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Ultra-violet rays from the sun.  They cause skin cancer, sunburn, and more.
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I haven't heard much about how far away you should sit, except that it should be comfortable for you.  I wanted to comment on another answer that stated that you should turn down the brightness to decrease the amount of radiation.  There's been a lot of hype about UV radiation from computer screens lately and actually, monitors emit UV at a level 10,000 to 100,000 times LOWER than the levels known to cause any eye or skin damage.  Also, make sure that you take breaks about every 20 minutes when you're working on the computer to relax your eyes.