Final answer:
A blackbody is an idealized physical entity that perfectly absorbs and re-emits all incident electromagnetic radiation across the entire spectrum. The concept is used to model the thermal emission of objects like stars and heated cavities with a small hole, which emit radiation known as blackbody radiation.
Step-by-step explanation:
What is a Blackbody?
A blackbody in physics is an idealized object that absorbs all electromagnetic radiation that falls upon it, regardless of frequency or angle of incidence. This absorbed energy is then re-emitted across the entire electromagnetic spectrum. The spectral distribution of the emitted radiation is characteristic of the blackbody's temperature, a relationship described by Planck's law of blackbody radiation.
An example that illustrates the concept of a blackbody is the thought experiment of a sealed oven with a small hole. As the oven's temperature increases, the hole emits radiation in various colors. At lower temperatures, the radiation might not be visible, resembling infrared emissions, but as the temperature rises, the hole can glow red, progressing through the visible spectrum, indicating an increase in the emitted radiation's frequency and energy.
Despite being an idealization, certain physical systems, such as stars including our own sun, are often approximated as blackbodies because they absorb and re-emit radiation over a wide range of wavelengths. The theory of blackbody radiation is essential for understanding thermal emission spectra of various bodies in space.