The total energy radiated per unit surface area of a blackbody across all wavelengths per unit time (also known as the blackbody emissive power) is directly proportional to the fourth power of the blackbody's absolute temperature.
Mathematically, this is expressed as:
E = σT⁴
where:
* E is the blackbody emissive power (energy radiated per unit surface area per unit time) in watts per square meter (W/m²)
* σ is the Stefan-Boltzmann constant, which has a value of 5.670374 × 10⁻⁸ W m⁻² K⁻⁴
* T is the absolute temperature of the blackbody in Kelvin (K)
Key points to remember:
* Blackbody: An ideal object that absorbs all radiation incident upon it and emits radiation at all wavelengths. While no real object is a perfect blackbody, many objects can be approximated as such.
* Total energy: The law describes the total energy radiated across all wavelengths.
* Fourth power: The emissive power is directly proportional to the fourth power of the temperature, meaning a small change in temperature can lead to a significant change in the amount of radiation emitted.
* Applications: The Stefan-Boltzmann law is widely used in various fields, including astrophysics, heat transfer, and climate science, to understand and calculate the energy emitted by stars, planets, and other celestial bodies.
Examples:
* The Sun, being approximately a blackbody, emits a large amount of radiation due to its high temperature (around 5778 K).
* A hot iron emits a visible red glow, which is a result of the increased radiation emitted as its temperature rises.
The Stefan-Boltzmann law is a fundamental principle in physics and plays a crucial role in understanding the transfer of energy through radiation.
