The term blackbody radiation refers to electromagnetic radiation emitted by a perfectly black object. Such an object is referred to as a blackbody since it absorbs all of the radiation that falls on it and thus appears to be colorless, or black. According to Kirchoff’s law, first stated by Gustav Kirchoff (1824–1887) in 1859, any blackbody must also be a perfect emitter of radiation.
No real object fits the definition of a blackbody since any material reflects some small fraction of the light falling upon it. Soot, carbon black, platinum black, and carborundum are among the real-world materials that come closest to having blackbody properties.
The concept of an idealized blackbody is important in physics. It serves as a standard for heat and temperature measurements just as the wavelength of light emitted by krypton-86 atoms is a standard for measurements of length.
For research purposes, physicists replicate the principle of a blackbody with a device known as a cavity radiator. A cavity radiator is a hollow sphere with a small hole through which radiation can enter and leave. Radiation that enters the hole is reflected continuously within the sphere until it is completely absorbed (as would be the case with a blackbody). It follows, then, that any radiation emitted by the cavity radiator corresponds to the definition of blackbody radiation.
The study of blackbody radiation was of considerable interest to physicists in the late 1800s. Experiments showed that for any given temperature, the intensity (brightness) of blackbody radiation is a maximum for a relatively narrow range of wavelengths, dropping off sharply at shorter and longer wavelengths. A number of attempts were made to use classical electromagnetic theory to derive a mathematical formula that would describe the intensity/wavelength relationship, but all failed for one or another part of the curve. Finally, in 1900, the German physicist Max Planck (1858–1947) solved the problem. By assuming that radiation travels not in continuous waves, but in discrete “packages” (called quanta), Planck was able to derive a formula for the blackbody radiation curve. That formula is as follows:
I = (ħc2/λ5)[exp(ħc/λkT – 1]–1
where ħ is Planck’s constant, k is Boltzmann’s constant, λ is the wavelength of the radiation, and T is temperature in Kelvins.
"Blackbody radiation." The Gale Encyclopedia of Science. . Encyclopedia.com. (August 19, 2019). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/blackbody-radiation
"Blackbody radiation." The Gale Encyclopedia of Science. . Retrieved August 19, 2019 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/blackbody-radiation
Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).
Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.
Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:
Modern Language Association
The Chicago Manual of Style
American Psychological Association
- Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
- In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.