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The extinction law's primary application is in chemical analysis, where it underlies the Beer–Lambert law, commonly called Beer's law. Beer's law states that a beam of visible light passing through a chemical solution of fixed geometry experiences absorption proportional to the solute concentration .
The absorbance of a material that has only one absorbing species also depends on the pathlength and the concentration of the species, according to the Beer–Lambert law =, where ε is the molar absorption coefficient of that material; c is the molar concentration of those species; ℓ is the path length.
The Beer–Lambert law states that there is a logarithmic dependence between the transmission (or transmissivity), T, of light through a substance and the product of the absorption coefficient of the substance, α, and the distance the light travels through the material (i.e. the path length), ℓ.
In physics, the attenuation length or absorption length is the distance λ into a material when the probability has dropped to 1/e that a particle has not been absorbed. ...
Both Beer's Law and Planck's Law can be derived from Schwarzschild's equation. [14] In a sense, they are corollaries of Schwarzschild's equation. When the spectral intensity of radiation is not changing as it passes through a medium, dI λ = 0. In that situation, Schwarzschild's equation simplifies to Planck's law:
It is assumed that the Beer–Lambert law applies. A = l ∑ ε c {\displaystyle A=l\sum {\varepsilon c}} where l is the optical path length, ε is a molar absorbance at unit path length and c is a concentration.
The gas constant R is defined as the Avogadro constant N A multiplied by the Boltzmann constant k (or k B): = = 6.022 140 76 × 10 23 mol −1 × 1.380 649 × 10 −23 J⋅K −1 = 8.314 462 618 153 24 J⋅K −1 ⋅mol −1. Since the 2019 revision of the SI, both N A and k are defined with exact numerical values when expressed in SI units. [2]
The constants listed here are known values of physical constants expressed in SI units; that is, physical quantities that are generally believed to be universal in nature and thus are independent of the unit system in which they are measured. Many of these are redundant, in the sense that they obey a known relationship with other physical ...