What is black body radiation?

Black body radiation is the electromagnetic radiation emitted by an idealised object that absorbs all incident radiation.

A black body is a theoretical object that is a perfect absorber and emitter of all wavelengths of electromagnetic radiation. When a black body is heated, it emits radiation across a range of wavelengths, and the distribution of this radiation depends solely on the temperature of the body. This concept is crucial in understanding how objects emit and absorb energy.

The radiation emitted by a black body is called black body radiation, and it follows a specific pattern described by Planck's law. As the temperature of the black body increases, the peak wavelength of the emitted radiation shifts to shorter wavelengths. This means that hotter objects emit more radiation at higher frequencies. For example, a red-hot object emits most of its radiation in the infrared and visible red spectrum, while a white-hot object emits across the visible spectrum, appearing white.

The study of black body radiation led to significant developments in physics, including the birth of quantum mechanics. Classical physics could not explain the observed spectrum of black body radiation, leading to what was known as the "ultraviolet catastrophe." Max Planck resolved this by proposing that energy is quantised, meaning it can only be emitted or absorbed in discrete amounts called quanta. This idea was revolutionary and laid the groundwork for modern quantum theory.

Understanding black body radiation is essential in various fields, including astrophysics, where it helps scientists determine the temperature and properties of stars and other celestial bodies. It also has practical applications in designing thermal cameras and improving the efficiency of heating and lighting systems.