Kirchhoff's law of thermal radiation

E93639

law of thermal radiation law of thermodynamics physical law

Kirchhoff's law of thermal radiation is a fundamental principle in thermodynamics stating that, for a body in thermal equilibrium, its emissivity equals its absorptivity at each wavelength.

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Observed surface forms (3)

Surface form	Occurrences
Kirchhoff's law of spectroscopy	1
Kirchhoff's law of thermal emission	1
Kirchhoff’s law of thermal radiation	1

Statements (49)

Predicate	Object
instanceOf	law of thermal radiation ⓘ law of thermodynamics ⓘ physical law ⓘ
appliedIn	astrophysics ⓘ climate science ⓘ material science ⓘ remote sensing ⓘ thermal engineering ⓘ
appliesTo	bodies in thermal equilibrium ⓘ opaque bodies ⓘ partially transparent bodies ⓘ
assumes	no net energy exchange at equilibrium ⓘ
category	conservation law consequence ⓘ
condition	local thermodynamic equilibrium ⓘ thermal equilibrium with surroundings ⓘ
consequence	emissivity cannot exceed absorptivity at a given wavelength in equilibrium ⓘ surface color affects both absorption and emission similarly at a given wavelength ⓘ
contrastWith	non-equilibrium radiative processes ⓘ
coreStatement	For a body in thermal equilibrium, spectral emissivity equals spectral absorptivity at each wavelength. ⓘ
dependsOn	temperature ⓘ wavelength ⓘ
field	heat transfer ⓘ radiative transfer ⓘ statistical mechanics ⓘ thermodynamics ⓘ
hasAlternativeLabel	Kirchhoff's law of thermal emission NERFINISHED ⓘ
implies	good absorbers are good emitters ⓘ poor absorbers are poor emitters ⓘ
language	English name ⓘ
mathematicalForm	ε(λ,T) = α(λ,T) for a body in thermal equilibrium ⓘ
namedAfter	Gustav Kirchhoff NERFINISHED ⓘ
proposedBy	Gustav Kirchhoff NERFINISHED ⓘ
relatedTo	Kirchhoff's circuit laws NERFINISHED ⓘ Kirchhoff's law of thermal radiation self-linksurface differs ⓘ surface form: Kirchhoff's law of thermal emission
relatesConcept	black-body emissive power ⓘ gray body ⓘ radiative equilibrium ⓘ spectral radiance ⓘ
relatesQuantity	absorptivity ⓘ emissivity ⓘ
scope	each wavelength separately ⓘ spectral quantities ⓘ
supports	concept of black body ⓘ
symbolDefinition	α is spectral absorptivity ⓘ ε is spectral emissivity ⓘ
usedInDerivationOf	Planck radiation law ⓘ surface form: Planck's law of black-body radiation Stefan–Boltzmann law ⓘ Wien's displacement law NERFINISHED ⓘ
yearProposed	1859 ⓘ

Referenced by (4)

Full triples — surface form annotated when it differs from this entity's canonical label.

Gustav Kirchhoff → notableWork → Kirchhoff's law of thermal radiation ⓘ

this entity surface form: Kirchhoff's law of spectroscopy

Kirchhoff's law of thermal radiation → relatedTo → Kirchhoff's law of thermal radiation self-linksurface differs ⓘ

this entity surface form: Kirchhoff's law of thermal emission

Stefan–Boltzmann law → relatedTo → Kirchhoff's law of thermal radiation ⓘ

this entity surface form: Kirchhoff’s law of thermal radiation