Black Body Radiation
Introduction
Black body radiation is a theoretical concept in the field of quantum mechanics, which refers to the electromagnetic radiation emitted by a perfect absorber - a black body. A black body absorbs all incident radiation, regardless of frequency or angle of incidence. The radiation emitted by such a body is called black body radiation.
Historical Background
The concept of black body radiation has its roots in the 19th century when scientists were trying to understand the nature of heat and light. The term "black body" was coined by Gustav Robert Kirchhoff in 1862. He used it to describe an idealized physical body that absorbs all incident electromagnetic radiation.
Planck's Law
In 1900, Max Karl Ernst Ludwig Planck proposed a theoretical model to explain the spectral density of black body radiation, which is now known as Planck's law. According to this law, the energy of each quantum is proportional to its frequency, a proportionality represented by Planck's constant.
Wien's Displacement Law
Another important aspect of black body radiation is Wien's displacement law, proposed by Wilhelm Carl Werner Otto Fritz Franz Wien in 1893. This law states that the wavelength at which the radiation emitted by a black body is maximum is inversely proportional to its temperature.
Stefan-Boltzmann Law
The Stefan-Boltzmann law, named after Jozef Stefan and Ludwig Eduard Boltzmann, is another fundamental principle related to black body radiation. This law states that the total energy radiated per unit surface area of a black body is directly proportional to the fourth power of its absolute temperature.
Rayleigh-Jeans Law
The Rayleigh-Jeans law, derived by Lord Rayleigh (John William Strutt) and Sir James Jeans around 1900, describes the spectral radiance of black body radiation at different wavelengths at a fixed temperature. However, this law was found to fail at short wavelengths, leading to what is known as the "ultraviolet catastrophe".
Ultraviolet Catastrophe
The ultraviolet catastrophe was a prediction of the Rayleigh-Jeans law that the energy of black body radiation at short wavelengths would be infinite, which contradicts the principles of conservation of energy. This problem was resolved by Planck's law, which accurately describes the black body radiation spectrum at all wavelengths.
Significance and Applications
Black body radiation has significant implications in various fields of physics, including thermodynamics, quantum mechanics, and statistical mechanics. It is also crucial in astrophysics for the study of stellar bodies, as stars can be approximated as black bodies. Furthermore, the concept of black body radiation is fundamental to the understanding of the cosmic microwave background radiation.