# Gustav Kirchhoff

Gustav Kirchhoff
Gustav Kirchhoff
Born Gustav Robert Kirchhoff
12 March 1824
Königsberg, Province of East Prussia in the Kingdom of Prussia
Died 17 October 1887 (aged 63)
Berlin, Province of Brandenburg in the Kingdom of Prussia, a part of the German Empire
(present-day Germany)
Residence Prussia/German Empire
Nationality Prussian (until 1871)
German (after 1871)
Alma mater University of Königsberg
Known for Kirchhoff's circuit laws
Kirchhoff's laws of spectroscopy
Kirchhoff's law of thermochemistry
Awards Rumford medal (1862)
Davy Medal (1877)
Matteucci Medal (1877)
Janssen Medal (1887)
Scientific career
Fields Physics
Chemistry
Institutions University of Berlin
University of Breslau
University of Heidelberg
Doctoral advisor Franz Ernst Neumann[citation needed]
Notable students Loránd Eötvös
Edward Nichols
Gabriel Lippmann[citation needed]
Dmitri Ivanovich Mendeleev
Max Planck
Jules Piccard
Max Noether
Heike Kamerlingh Onnes
Ernst Schröder

Gustav Robert Kirchhoff (German: [ˈkɪʁçhɔf]; 12 March 1824 – 17 October 1887) was a German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects.

He coined the term black-body radiation in 1862, and at least two different sets of concepts are named "Kirchhoff's laws" after him. The Bunsen–Kirchhoff Award for spectroscopy is named after him and his colleague, Robert Bunsen.

## Life and work

Gustav Kirchhoff was born in Königsberg, Prussia, the son of Friedrich Kirchhoff, a lawyer, and Johanna Henriette Wittke. His family were Lutherans in the Evangelical Church of Prussia. He graduated from the Albertus University of Königsberg in 1847 where he attended the mathematico-physical seminar directed by Carl Gustav Jacob Jacobi,[1] Franz Ernst Neumann and Friedrich Julius Richelot. In the same year, he moved to Berlin, where he stayed until he received a professorship at Breslau. Later, in 1857, he married Clara Richelot, the daughter of his mathematics professor Richelot. The couple had five children. Clara died in 1869. He married Luise Brömmel in 1872.[2]

Gustav Kirchhoff (left) and Robert Bunsen (right)

Kirchhoff formulated his circuit laws, which are now ubiquitous in electrical engineering, in 1845, while still a student. He completed this study as a seminar exercise; it later became his doctoral dissertation. In 1857 he calculated that an electric signal in a resistanceless wire travels along the wire at the speed of light.[3][4] He proposed his law of thermal radiation in 1859, and gave a proof in 1861. He was called to the University of Heidelberg in 1854, where he collaborated in spectroscopic work with Robert Bunsen. Together Kirchhoff and Bunsen discovered caesium and rubidium in 1861. At Heidelberg he ran a mathematico-physical seminar, modelled on Neumann's, with the mathematician Leo Koenigsberger. Among those who attended this seminar were Arthur Schuster and Sofia Kovalevskaya. In 1875 Kirchhoff accepted the first chair specifically dedicated to theoretical physics at Berlin.

In 1862 he was awarded the Rumford Medal for his researches on the fixed lines of the solar spectrum, and on the inversion of the bright lines in the spectra of artificial light.

He contributed greatly to the field of spectroscopy by formalizing three laws that describe the spectral composition of light emitted by incandescent objects, building substantially on the discoveries of David Alter and Anders Jonas Ångström (see also: spectrum analysis).

He also contributed to optics, carefully solving Maxwell's equations to provide a solid foundation for Huygens' principle (and correct it in the process).[5]

In 1884 he became foreign member of the Royal Netherlands Academy of Arts and Sciences.[6]

Kirchhoff died in 1887, and was buried in the St Matthäus Kirchhof Cemetery in Schöneberg, Berlin (just a few meters from the graves of the Brothers Grimm). Leopold Kronecker is buried in the same cemetery.

## Kirchhoff's circuit laws

Kirchhoff's first law is that the algebraic sum of currents in a network of conductors meeting at a point (or node) is zero. The second law is that in a closed circuit, the directed sums of the voltages in a closed system is zero.

## Kirchhoff's three laws of spectroscopy

Visual depiction of Kirchhoff laws or spectroscopy
Spectroscope of Kirchhoff and Bunsen
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. (See also: emission spectrum)
3. If light composing a continuous spectrum passes through a cool, low-density gas, the result will be an absorption spectrum.

Kirchhoff did not know about the existence of energy levels in atoms. The existence of discrete spectral lines was later explained by the Bohr model of the atom, which helped lead to quantum mechanics.

## Kirchhoff's law of thermochemistry

Kirchhoff showed in 1858 that, in thermochemistry, the variation of the heat of a chemical reaction is given by the difference in heat capacity between products and reactants:

${\displaystyle \left({\frac {\partial \Delta H}{\partial T}}\right)_{p}=\Delta C_{p}}$.

Integration of this equation permits the evaluation of the heat of reaction at one temperature from measurements at another temperature.[7][8]

## Notes

1. ^ Hockey, Thomas (2009). "Kirchhoff, Gustav Robert". The Biographical Encyclopedia of Astronomers. Springer Publishing. ISBN 978-0-387-31022-0. Retrieved August 22, 2012.
2. ^ "Gustav Robert Kirchhoff - Dauerausstellung". Kirchhoff-Institute for Physics. Retrieved 18 Mar 2016. Am 16. August 1857 heiratete er Clara Richelot, die Tochter des Königsberger Mathematikers ... Frau Clara starb schon 1869. Im Dezember 1872 heiratete Kirchhoff Luise Brömmel.
3. ^ Kirchhoff, G. (1857). "On the motion of electricity in wires". Philosophical Magazine. 13: 393–412.
4. ^ Graneau, P.; Assis, A.K.T. (1994). "Kirchhoff on the motion of electricity in conductors" (PDF). Apeiron. 1 (19): 19–25.
5. ^ D. Miller, "Huygens’s wave propagation principle corrected", Opt. Lett. 16, 1370–1372 (1991)
6. ^ "G.R. Kirchhoff (1824 - 1887)". Royal Netherlands Academy of Arts and Sciences. Retrieved 22 July 2015.
7. ^ Laidler K.J. and Meiser J.H., "Physical Chemistry" (Benjamin/Cummings 1982), p.62
8. ^ Atkins P. and de Paula J., "Atkins' Physical Chemistry" (8th edn, W.H. Freeman 2006), p.56