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Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)". [1] Alternatively, for samples which scatter light, absorbance may be defined as "the negative logarithm of one minus absorptance, as measured on a uniform sample". [2]
In physics, the D-region of Earth's ionosphere is known to significantly absorb radio signals that fall within the high-frequency electromagnetic spectrum. In nuclear physics, absorption of nuclear radiations can be used for measuring the fluid levels, densitometry or thickness measurements. [2]
This should not be confused with "absorbance". Spectral hemispherical absorptance: A ν A λ — Spectral flux absorbed by a surface, divided by that received by that surface. This should not be confused with "spectral absorbance". Directional absorptance: A Ω — Radiance absorbed by a surface, divided by the radiance incident onto that surface.
However, there is also a specific, quantitative definition of "opacity", used in astronomy, plasma physics, and other fields, given here. In this use, "opacity" is another term for the mass attenuation coefficient (or, depending on context, mass absorption coefficient , the difference is described here ) κ ν {\displaystyle \kappa _{\nu }} at ...
Transmittance of ruby in optical and near-IR spectra. Note the two broad blue and green absorption bands and one narrow absorption band on the wavelength of 694 nm, which is the wavelength of the ruby laser. In optical physics, transmittance of the surface of a material is its effectiveness in transmitting radiant energy.
The specificity of absorption spectra allows compounds to be distinguished from one another in a mixture, making absorption spectroscopy useful in wide variety of applications. For instance, Infrared gas analyzers can be used to identify the presence of pollutants in the air, distinguishing the pollutant from nitrogen, oxygen, water, and other ...
Specific energy absorption rate (SAR) averaged over the whole body or over parts of the body, is defined as the rate at which energy is absorbed per unit mass of body tissue and is expressed in watts per kilogram (W/kg). Whole body SAR is a widely accepted measure for relating adverse thermal effects to RF exposure. [9]
In science, absorptivity may refer to: Molar absorptivity, in chemistry, a measurement of how strongly a chemical species absorbs light at a given wavelength; Absorptance, in physics, the fraction of radiation absorbed at a given wavelength; Emissivity § Absorptivity, information on the radiometrical aspect