Blackbody radiation

nicolelyu812
Aug 18, 2024
1 min read

"I'm radiating!!!" "Yes you sure are :)"

Thermal radiation is radiation that all objects with temperature above absolute zero emit. In particular, blackbody radiation is thermal radiation from a black body (a perfect absorber and emitter) in thermodynamic equilibrium (in constant temperature), and it is a type of electromagnetic wave. Black-body radiation is usually in the infrared spectrum, but if the temperature is high enough (over about 500 degrees Celsius), the peak emission wavelength/frequency can advance to visible light, so hot stuff glow. The peak frequency is directly proportional to temperature, and the peak wavelength is inversely proportional to temperature, given by Wien’s displacement law. The total amount of power emitted is directly proportional to temperature to the fourth power, given by the Stefan-Boltzmann law.

The black-body radiation spectrum could easily be represented by a graph, with the y axis being the spectral energy density and the x axis being frequency (or wavelength). A black body radiates As the frequency is low, energy density increases with frequency, reaching a peak energy density at a certain frequency then approaches zero as frequency tends to infinity. The area under the curve is the total power of black-body radiation.

Real objects can never be full-ideal black bodies. But the Prize of best effort goes to the cosmic microwave background radiation - it is the closest-to-perfect black body ever observed in nature, exhibiting a near perfect black-body spectrum. In order to study black-body radiation in a laboratory, a device called hohlraum is used, consisting of a small hole in a large cavity.