Planck's Law & Blackbody Radiation
The foundational law describing the spectral radiance of electromagnetic radiation emitted by a blackbody in thermal equilibrium.
Governing formula
B_ν(T) = (2 h ν³ / c²) / (e^(h ν / (k_B T)) - 1), E = h ν
SI unit
W / (m²·sr·Hz)
In depth
Formulated by Max Planck in 1900, Planck introduced the revolutionary hypothesis that electromagnetic energy is emitted in discrete quanta E = hν, successfully solving the ultraviolet catastrophe of classical Rayleigh-Jeans theory.
Examples in the real world
Calculating the cosmic microwave background (CMB) spectrum matching a 2.725 K ideal blackbody curve.