Quantum Mechanics/Blackbody Radiation

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Black-body radiation is the thermal electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body (an opaque and non-reflective body). It has a specific spectrum and intensity that depends only on the body's temperature, which is assumed for the sake of calculations and theory to be uniform and constant.

Considering a cavity at temperature in radiation equilibrium,the volume of the cavity is , the energy density (energy per unit volume and frequency) . Here expresses the energy per unit volume in the interval. Classically, the situation is described by the Rayleigh–Jeans law .One can easily make this plausible by considering standing plane waves in a cavity with reflecting metal walls.

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