Gustav Robert Kirchhoff (1824 - 1887) was a German physicist with scientific contributions mainly in the field of electrical circuits, spectroscopy, blackbody radiation and elasticity theory (Kirchhoff plate model). Kirchhoff proposed the name "blackbody radiation" in 1862. He is the author of two fundamental laws of the classical theory of electrical circuits and thermal emission.
Kirchhoff was born in Königsberg, Prussia (currently Kaliningrad, Russia). Son of Friedrich Kirchhoff (lawyer) and Johanna Henriette. He graduated from Albertus University of Königsberg in 1847, where he attended the mathematical physics seminars under the direction of Franz Ernst Neumann and Friedrich Julius Richelot. He married Clara Richelot, daughter of Richelot, one of his math teachers. In the same year he moved to Berlin, receiving the post of Professor in Wrocław.
Kirchhoff formulated knot and loop laws in electrical circuit analysis (Kirchhoff Laws) in 1845, while still a student. He proposed the thermal radiation emission law in 1859, proving it in 1861. In 1854 he moved to the University of Heidelberg, where he collaborated on work on spectroscopy with Robert Bunsen, discovering with him the cesium and rubidium elements in 1861, studying the chemical composition of the sun through its spectrum.
He later proposed the three laws that describe the emission of light by incandescent objects:
- A heated solid object produces light with continuous spectrum.
- A faint gas produces light with discrete wavelength spectral lines that depend on the chemical composition of the gas.
- A high temperature solid object surrounded by a faint gas at lower temperatures produces light in a continuous spectrum with voids at discrete wavelengths whose positions depend on the chemical composition of the gas.
The existence of these laws was later explained by Niels Bohr, contributing decisively to the birth of quantum mechanics.
Kirchhoff was buried in the St. Matthew Community Cemetery (Friedhof der St. Matthäi-Gemeinde) in Berlin.