Fourier's law

Fourier's law describes how heat flows through materials in response to temperature differences. Formulated by Jean-Baptiste Joseph Fourier in the early 19th century, this principle states that the rate of heat transfer is proportional to the temperature gradient—steeper gradients mean faster heat flow. It's a cornerstone of thermodynamics and essential for understanding everything from cooking to industrial processes.

The law applies to heat conduction, where thermal energy spreads through a medium without bulk motion. Mathematically, it's expressed as a differential equation relating heat flux (energy per unit time and area) to the spatial temperature change. This makes it crucial for engineering applications: designing insulation, predicting cooling rates, optimizing heat exchangers, and even understanding how photons and electrons transfer energy at scales both macroscopic and microscopic.

Fourier's law assumes local thermal equilibrium and works remarkably well under ordinary conditions. However, in extreme environments—near absolute zero or inside intense radiation fields—corrections become necessary, opening doors to deeper physics.

Related

Jean-Baptiste Joseph Fourier, Heat transfer, Temperature gradient, Thermal conductivity, Second Law of Thermodynamics, Differential equations