What is the Stefan-Boltzmann law in radiation?

The Stefan-Boltzmann 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.

The Stefan-Boltzmann law is a fundamental principle in the field of thermal radiation, which is the process by which energy is emitted by a heated object in the form of electromagnetic waves. Named after physicists Josef Stefan and Ludwig Boltzmann, this law provides a mathematical relationship between the energy radiated by a black body (an idealised physical body that absorbs all incident electromagnetic radiation) and its temperature.

The law is expressed mathematically as E = σT^4, where E is the energy radiated per unit surface area, T is the absolute temperature of the body (measured in Kelvin), and σ is the Stefan-Boltzmann constant. This constant is a universal physical constant denoted by the Greek letter 'sigma', and its value is approximately 5.67 x 10^-8 watt per square metre per Kelvin to the power of 4.

The Stefan-Boltzmann law is significant because it allows us to calculate the amount of energy a body will radiate based on its temperature. This is particularly useful in astrophysics, where it is used to determine the temperature of stars and other celestial bodies. For example, our Sun, which is considered a black body, radiates energy according to this law.

It's important to note that the Stefan-Boltzmann law applies only to ideal black bodies and perfect radiators. Real-world objects may not follow this law exactly due to factors such as reflectivity and emissivity. However, it provides a good approximation for many physical systems and is a key concept in the study of thermal physics.