Gustav Kirchhoff
German physicist and mathematician known for Kirchhoff's circuit laws, spectroscopy, and black-body radiation.
Gustav Robert Kirchhoff was a German physicist and mathematician whose work laid the groundwork for modern electrical engineering, spectroscopy, and the study of thermal radiation. Born on 12 March 1824 in Königsberg, Prussia, he was the son of a lawyer, Friedrich Kirchhoff, and Johanna Henriette Wittke; his family belonged to the Lutheran Evangelical Church of Prussia. He studied at the University of Königsberg, taking part in a mathematico-physical seminar led by C. G. J. Jacobi, Franz Ernst Neumann, and Friedrich Julius Richelot. In 1845, as a seminar exercise, Kirchhoff formulated two fundamental circuit laws, which later became his doctoral thesis under Neumann’s supervision. After graduating in 1847, he worked as an unsalaried lecturer at the University of Berlin until 1850, when he became a professor at the University of Breslau. In 1854, he moved to the University of Heidelberg, where he collaborated with Robert Bunsen on spectroscopy. He returned to Berlin in 1875 and remained there until his death on 17 October 1887. He was buried at Alter St.-Matthäus-Kirchhof in Schöneberg, Berlin, near the graves of the Brothers Grimm. Kirchhoff married Clara Richelot, his mathematics professor’s daughter, in 1857; they had five children. After Clara’s death in 1869, he married Luise Brömmel in 1872.
Kirchhoff’s research spanned several fields. In 1850, he resolved a long-standing flaw in plate theory by correctly handling boundary conditions, using the calculus of variations on strain energy to show that twisting moments along an edge are equivalent to vertical shear forces. This made the plate’s biharmonic eigenvalue problem well-posed and led to what is now called Kirchhoff–Love plate theory. In 1857, he calculated that an electric signal in a resistanceless wire travels at the speed of light. In 1859, he proposed a law of thermal radiation, proving it in 1861, and coined the term “black body” in 1860. With Bunsen, he improved on Fraunhofer’s spectroscope and used it to identify sodium in the Sun in 1859; together they discovered caesium and rubidium in 1861. Kirchhoff formalized three laws of spectroscopy describing how light is emitted and absorbed by different states of matter: a solid, liquid, or dense gas produces a continuous spectrum; a low-density gas emits light at specific wavelengths, creating an emission spectrum; and a continuous spectrum passing through a cool, low-density gas yields an absorption spectrum. He also contributed to optics by solving the wave equation to refine Huygens’ principle. In 1862, he received the Rumford Medal for his work on solar spectral lines and the inversion of bright lines in artificial light.
Several sets of concepts bear his name: Kirchhoff’s circuit laws (the first stating that current entering a node equals current leaving it, and the second that the sum of voltage drops around a closed loop is zero), Kirchhoff’s law of thermal radiation, Kirchhoff’s diffraction formula, and Kirchhoff’s law of thermochemistry. The Bunsen–Kirchhoff Award for spectroscopy honors him and his colleague.
- born
- 12 March 1824 in Königsberg, Prussia
- died
- 17 October 1887 in Berlin, Germany
- field
- Physics, Mathematics
- nationality
- German
- known_for
- Kirchhoff's circuit laws, Kirchhoff's law of thermal radiation, Kirchhoff's three laws of spectroscopy, Kirchhoff's law of thermochemistry, Kirchhoff's diffraction formula, Kirchhoff's matrix tree the
Lore & Background
Gustav Robert Kirchhoff was born on 12 March 1824 in Königsberg, Prussia, the son of Friedrich Kirchhoff, a lawyer, and Johanna Henriette Wittke. His family were Lutherans in the Evangelical Church of Prussia. Kirchhoff studied at the University of Königsberg, where he attended the mathematico-physical seminar directed by C. G. J. Jacobi, Franz Ernst Neumann, and Friedrich Julius Richelot. In 1845, Kirchhoff formulated two circuit laws, which are now ubiquitous in electrical engineering. He completed this study as a seminar exercise; it later became his doctoral thesis, supervised by Neumann. In 1847, Kirchhoff graduated from the University of Königsberg and became a Privatdozent (unsalaried lecturer) at the University of Berlin, where he stayed until 1850 when he was offered a professorship at the University of Breslau. In 1854, he was called to the University of Heidelberg, where he collaborated with Robert Bunsen in spectroscopic work. In 1875, Kirchhoff returned to Berlin, where he remained until his death in 1887. In 1857, Kirchhoff married Clara Richelot, the daughter of his mathematics professor Richelot; the couple had five children. In 1872, after Clara's death in 1869, he married Luise Brömmel. Kirchhoff died on 17 October 1887 in Berlin at the age of 63. He is buried at Alter St.-Matthäus-Kirchhof in Schöneberg, Berlin (just a few meters from the graves of the Brothers Grimm).
Reader's Guide
Kirchhoff's first law states that at any node in an electrical circuit where current can branch, the sum of the currents leaving the node is equal to the sum of the currents entering the node. The second law states that the algebraic sum of the potential drops along a closed circuit, taken in any direction of flow, is equal to zero. Kirchhoff's three laws of spectroscopy: (1) A solid, liquid, or dense gas excited to emit light will radiate at all wavelengths and thus produce a continuous spectrum. (2) A low-density gas excited to emit light will do so at specific wavelengths, and this produces an emission spectrum. (3) If light composing a continuous spectrum passes through a cool, low-density gas, the result will be an absorption spectrum. Kirchhoff's law of thermal radiation proposed an unknown universal law for radiation that led Max Planck to the discovery of the quantum of action. Kirchhoff's law of thermochemistry (1858) states that the variation of the heat of a chemical reaction is given by the difference in heat capacity between products and reactants. Kirchhoff also contributed to optics, carefully solving the wave equation to provide a solid foundation for Huygens' principle.
Did You Know?
- Kirchhoff coined the term 'black body' in 1860.
- In 1857, Kirchhoff calculated that an electric signal in a resistanceless wire travels along the wire at the speed of light.
- Kirchhoff and Bunsen discovered caesium and rubidium in 1861.
- Kirchhoff's plate theory resolved a boundary condition problem that had dogged plate theory since Germain's original work.
Notable Quotes (Wikiquote)
"Look here, I have succeeded at last in fetching some gold from the sun." — Gustav Kirchhoff "after his banker questioned the value of investigating gold in the Fraunhofer lines of the sun and Kirchhoff handing him over a medal he was awarded for his investigations." — Gustav Kirchhoff "A memoir of Gustav Robert Kirchhoff, by Robert Von Helmholtz, translated by Joseph De Perott, in Annual Report of the Board of Regents of the Smithsonian Institution, Smithsonian Institution (1890), p. 537." — Gustav Kirchhoff "Heat rays have the same nature as light rays... The invisible heat rays are distinguished from light rays only by the period of vibration or the wave length." — Gustav Kirchhoff
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