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Chemical Sciences
Analytical Chemistry
1852
Intermediate

Beer-Lambert Law

A=εcA = \varepsilon \ell c

Absorbance of light through a solution is proportional to concentration and path length.

By August Beer, Johann Lambert

Chemical Sciences
Beer-Lambert Law
1852 · August Beer
Human Reviewed
84%

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Why it matters: Enabled spectrophotometry—the workhorse of chemical analysis.

Discoverers: August Beer, Johann Lambert (1852)

What does it mean?

Absorbance of light through a solution is proportional to concentration and path length.

Why should I care?

Enabled spectrophotometry—the workhorse of chemical analysis.

Equation Compass

North — Prerequisites

South — Derivations

Variables & Units

SymbolNameUnitMeaning
AAAbsorbanceLog of transmitted light
εεMolar absorptivityExtinction coefficient
Path lengthcmCuvette width
ccConcentrationmol/LMolar concentration

Worked Example

ε=5000, ℓ=1cm, c=0.001M → A=5 (may need dilution).

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Beer-Lambert Law

A=εcA = \varepsilon \ell c

Real-world impact

Life sciences

Mathematical models drive medicine and biotech.

Photo: Unsplash — laboratory

Absorbance of light through a solution is proportional to concentration and path length.

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