In meteorology and climatology, global and local temperatures depend in part on the absorption of radiation by atmospheric gases (such as in the greenhouse effect) and land and ocean surfaces (see albedo).For example, see computation of radio wave attenuation in the atmosphere used in satellite link design. In radio propagation, it is represented in non-line-of-sight propagation.Understanding and measuring the absorption of electromagnetic radiation has a variety of applications. A few examples of absorption are ultraviolet–visible spectroscopy, infrared spectroscopy, and X-ray absorption spectroscopy.Īpplications Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light Precise measurements of the absorbance at many wavelengths allow the identification of a substance via absorption spectroscopy, where a sample is illuminated from one side, and the intensity of the light that exits from the sample in every direction is measured. This may be related to other properties of the object through the Beer–Lambert law. The absorbance of an object quantifies how much of the incident light is absorbed by it (instead of being reflected or refracted). Which among them practitioners use varies by field and technique, often due simply to the convention. Related measures, including absorbance (also called "optical density") and optical depth (also called "optical thickness")Īll these quantities measure, at least to some extent, how well a medium absorbs radiation.
Absorption spectra example skin#
Other measures of radiation absorption, including penetration depth and skin effect, propagation constant, attenuation constant, phase constant, and complex wavenumber, complex refractive index and extinction coefficient, complex dielectric constant, electrical resistivity and conductivity."Extinction" in astronomy, which is equivalent to the attenuation coefficient.The absorption cross section and scattering cross-section, related closely to the absorption and attenuation coefficients, respectively.The mass attenuation coefficient (also called "mass extinction coefficient"), which is the absorption coefficient divided by density.The Molar attenuation coefficient (also called "molar absorptivity"), which is the absorption coefficient divided by molarity (see also Beer–Lambert law).The attenuation coefficient (NB used infrequently with meaning synonymous with "absorption coefficient").The absorption coefficient along with some closely related derived quantities.Many approaches can potentially quantify radiation absorption, with key examples following. Main article: Mathematical descriptions of opacity Although the absorption of waves does not usually depend on their intensity (linear absorption), in certain conditions ( optics) the medium's transparency changes by a factor that varies as a function of wave intensity, and saturable absorption (or nonlinear absorption) occurs. A notable effect is attenuation, or the gradual reduction of the intensity of light waves as they propagate through a medium. In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy - and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). By recording the attenuation of light for various wavelengths, an absorption spectrum can be obtained. Other photons are transmitted unaffected and, if the radiation is in the visible region (400–700 nm), the transmitted light appears as the complementary color (here red). Upon striking the sample, photons that match the energy gap of the molecules present (green light in this example) are absorbed, exciting the molecules. A white light source - emitting light of multiple wavelengths - is focused on a sample (the pairs of complementary colors are indicated by the yellow dotted lines). This example discusses the general principle using visible light as a specific example.
( November 2010) ( Learn how and when to remove this template message)Īn overview of electromagnetic radiation absorption. Please help to improve this article by introducing more precise citations. This article includes a list of general references, but it lacks sufficient corresponding inline citations.
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