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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All labels observed (4)

Label	Occurrences
Kirchhoff's law of thermal emission	2
Kirchhoff's law of spectroscopy	1
Kirchhoff's law of thermal radiation canonical	1
Kirchhoff’s law of thermal radiation	1

How this entity was disambiguated

This entity first appeared as the object of triple T793359 — resolving that mention is where its identity was fixed. The disambiguator weighed these candidate entities and picked the highlighted one (or “None”, minting a new entity). This is how homonymy is resolved: the same surface form can point to different entities.

NED1 Entity disambiguation (via context triple) gpt-5-mini-2025-08-07

Target entity: Kirchhoff's law of thermal radiation
Context triple: [Gustav Kirchhoff, notableWork, Kirchhoff's law of thermal radiation]

A. Stefan–Boltzmann law
The Stefan–Boltzmann law is a fundamental principle of thermal radiation stating that the total energy radiated per unit surface area of a black body is proportional to the fourth power of its absolute temperature.
B. Planck radiation law
Planck radiation law is a fundamental formula in quantum physics that describes the spectral distribution of electromagnetic radiation emitted by a black body in thermal equilibrium.
C. Wien displacement law
Wien's displacement law is a physical law that relates the temperature of a blackbody to the wavelength at which it emits radiation most intensely.
D. Fourier's law of heat conduction
Fourier's law of heat conduction is a fundamental physical principle that relates heat flux within a material to the negative gradient of temperature, forming the basis of classical heat transfer theory.
E. Rayleigh–Jeans law at low frequencies
The Rayleigh–Jeans law at low frequencies is the classical approximation for blackbody radiation that accurately describes the long-wavelength, low-energy limit of Planck’s radiation spectrum.
F. None of above. chosen
G. Unsure - the case is ambiguous/there is not enough information to decide.

NED2 Entity disambiguation (via description) gpt-5-mini-2025-08-07

Target entity: Kirchhoff's law of thermal radiation
Target entity description: 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.

A. Stefan–Boltzmann law
The Stefan–Boltzmann law is a fundamental principle of thermal radiation stating that the total energy radiated per unit surface area of a black body is proportional to the fourth power of its absolute temperature.
B. Planck radiation law
Planck radiation law is a fundamental formula in quantum physics that describes the spectral distribution of electromagnetic radiation emitted by a black body in thermal equilibrium.
C. Wien displacement law
Wien's displacement law is a physical law that relates the temperature of a blackbody to the wavelength at which it emits radiation most intensely.
D. Fourier's law of heat conduction
Fourier's law of heat conduction is a fundamental physical principle that relates heat flux within a material to the negative gradient of temperature, forming the basis of classical heat transfer theory.
E. Rayleigh–Jeans law at low frequencies
The Rayleigh–Jeans law at low frequencies is the classical approximation for blackbody radiation that accurately describes the long-wavelength, low-energy limit of Planck’s radiation spectrum.
F. None of above. chosen

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 radiation ⓘ surface form: Kirchhoff's law of thermal emission
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 ⓘ
proposedBy	Gustav Kirchhoff ⓘ
relatedTo	Kirchhoff's circuit laws ⓘ 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 displacement law ⓘ surface form: Wien's displacement law
yearProposed	1859 ⓘ

How these facts were elicited

Referenced by (5)

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

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

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

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

Kirchhoff's law of thermal radiation → hasAlternativeLabel → Kirchhoff's law of thermal radiation ⓘ