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What Is a Black Body (in Physics)?

PhysicsQuantum Mechanics

Quick Answer

A black body is an idealised object that absorbs all incoming electromagnetic radiation and re-emits it based solely on its temperature.

The Full Story

In physics, a black body is a theoretical perfect absorber and emitter of radiation. It absorbs every wavelength of light that hits it (reflecting nothing) and emits a characteristic spectrum determined entirely by its temperature — the black-body radiation curve. Max Planck derived the equation describing this spectrum in 1900, introducing the concept of energy quanta, which launched quantum mechanics. Real objects approximate black bodies: stars, molten metal, and even the cosmic microwave background radiation (the afterglow of the Big Bang at 2.725 K) closely follow the black-body curve.

Key Facts

1.Planck constant (h ≈ 6.626 × 10⁻³⁴ J·s), first introduced in the black-body radiation formula, became one of the fundamental constants of physics.
2.Wien displacement law states that hotter black bodies peak at shorter wavelengths — this is why hot stars appear blue and cooler stars appear red.
3.The cosmic microwave background is the most perfect black-body spectrum ever measured, with deviations smaller than one part in 100,000.

YouTube Angle

Suggested video title for this topic:

"Black-Body Radiation — The Discovery That Birthed Quantum Physics"