tailieunhanh - Science of Everyday Things Vol. 2 - Physics Episode 13

Tham khảo tài liệu 'science of everyday things vol. 2 - physics episode 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | LUMINESCENCE Like many marine creatures jellyfish produce their own light through phosphorescence. Photograph by Mark A. Johnson. The Stock Market. Reproduced by permission. Curie noted that calcium fluoride glows when exposed to a radioactive material known as radium. Curie who also coined the term radioactivity helped spark a revolution in science and technology. As a result of her work and the discoveries of others who followed interest in luminescence and luminescent devices grew. Today luminescence is applied in a number of devices around the household most notably in television screens and fluorescent lights. FluorESCENCE As indicated in the introduction to this essay the difference between the two principal types of luminescence relates to the timing of their reactions to electromagnetic radiation. Fluorescence is a type of luminescence whereby a substance absorbs radiation and almost instantly begins to re-emit the radiation. Actually the delay is 10-6 seconds or a millionth of a second. Fluorescent luminescence stops within 10-5 seconds after the energy source is removed thus it comes to an end almost as quickly as it begins. Usually the wavelength of the re-emitted radiation is longer than the wavelength of the radiation the substance absorbed. British mathe matician and physicist George Gabriel Stokes 1819-1903 who coined the term fluorescence first discovered this difference in wavelength. However in a special type of fluorescence known as resonance fluorescence the wavelengths are the same. Applications of resonance include its use in analyzing the flow of gases in a wind tunnel. BLACK LIGHTS AND FLUORESCENCE. A black light so called because it emits an eerie bluish-purple glow is actually an ultraviolet lamp and it brings out vibrant colors in fluorescent materials. For this reason it is useful in detecting art forgeries newer paint tends to fluoresce when exposed to ultraviolet light whereas older paint does not. Thus if a forger is trying to pass .

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