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(analytical chemistry)
The constant a in the Beer's law relation A = abc, where A is the absorbance, b the path length, and c the concentration of solution. Also known as absorptive power. Formerly known as absorbency index; absorption constant; extinction coefficient.
The ratio of the radiation absorbed by a surface to the total radiation incident on the surface.



(or absorptive power), αv, the fraction of a monochromatic radiation flux of frequency v that is absorbed by a body on which the flux is incident. Although often called the absorption factor, it differs from the absorption factor in that it applies only to radiation of a specific frequency. The absorption factor is the integral of the absorptivities over all the frequencies present in the irradiating flux. The absorptivity for thermal radiation is dependent not only on the frequency or wavelength of the radiation but also on the temperature T of the body:

α = α(ν, T) = α*(λ, T)


Landsberg, G. S. Optika, 4th ed. Moscow, 1957. (Obshchii kurs fiziki, vol. 3.)
References in periodicals archive ?
The absorptivity decreases steeply when the angle of incidence is changed from 90 degrees (absorptivity 80%) to an angle of 70[degrees] (absorptivity 20%) [13].
The combined effects of spectral absorptivity and physical thickness result in a distinct ratio of photon flux through the top of the film and the bottom.
In what follows we assume that the reference solution and the microbeads have the same fluorophore and that the molecular absorptivity is the same for the two.
It appears that roughness and species have some effect on absorptivity of the panels.
013 constant Absorptivity (initiator) [epsilon] 19.
V'/V is a measure of aggregate absorptivity (occlusion), employing the equivalent sphere model of Medalia (ref.
First, the condition under which Kirchhoff's law is often presented, the perfectly absorbing cavity, can be considered (emissivity ([member of]) = 1, absorptivity ([kappa]) = 1, reflectivity ([rho]) = 0; at the frequency of interest, v).
The effect of EPDM/a-MSt/ITA monomer composition ratio on the highest oil absorptivity is shown in Table 1.
Balfour Stewart [1] preceded Kirchhoff [2-4] by nearly two years in demonstrating, under equilibrium, the equality between absorptivity and emissivity.