What is Black-Body Radiation?
Black-body radiation refers to the thermal electromagnetic radiation emitted by an ideal physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. This hypothetical object, known as a "black body," then re-emits radiation based solely on its temperature, not on its composition or surface structure.
Characteristics and Planck's Law
The spectrum of black-body radiation is continuous and peaks at a specific wavelength inversely proportional to the body's temperature, as described by Wien's displacement law. Max Planck's revolutionary work in 1900, introducing the concept of quantized energy (photons), successfully explained the observed spectrum, resolving the "ultraviolet catastrophe" predicted by classical physics.
Real-World Examples
While a perfect black body doesn't exist, many objects behave similarly. A good example is the filament of an incandescent light bulb, which glows brightly when heated, emitting light across a spectrum that depends on its temperature. Another is the Cosmic Microwave Background (CMB) radiation, a relic from the early universe, which closely matches the spectrum of a black body at about 2.7 Kelvin.
Importance in Science and Technology
Understanding black-body radiation is fundamental to astrophysics for determining star temperatures and to climate science for modeling Earth's energy balance. It also laid the groundwork for quantum mechanics, profoundly influencing the development of modern physics and technologies such as infrared cameras and solar cells.