Gustav Kirchhoff

Gustav Robert Kirchhoff
Gustav Kirchhoff
Born	12 March, 1824 Königsberg, East Prussia
Died	17 October, 1887 Berlin, Germany
Residence	Germany
Nationality	German
Field	Physicist
Institutions	University of Berlin University of Breslau University of Heidelberg
Alma mater	University of Königsberg
Academic advisor	Franz Ernst Neumann
Notable students	Max Noether Ernst Schröder
Known for	Kirchhoff's circuit laws Kirchhoff's law of thermal radiation
Notable prizes	Rumford medal

Gustav Robert Kirchhoff (March 12, 1824 – October 17, 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 two sets of independent concepts in both circuit theory and thermal emission are named "Kirchhoff's laws" after him.

Gustav Kirchhoff was born in Königsberg, East Prussia, the son of Friedrich Kirchhoff, a lawyer, and Johanna Henriette Wittke. He graduated from the Albertus University of Königsberg in 1847 where he attended the mathematico-physical seminar directed by Franz Ernst Neumann and Friedrich Julius Richelot. He married Clara Richelot, the daughter of his mathematics professor Richelot. In the same year, they moved to Berlin, where he stayed until he received a professorship at Breslau.

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. 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 while studying the chemical composition of the Sun via its spectral signature. 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.

Kirchhoff died in 1887, and was buried in the St Matthäus Kirchhof Cemetery in Schöneberg, Berlin, only a few meters from the graves of the Brothers Grimm.

Spectroscopy research

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 Angstrom (see also: spectrum analysis)

Kirchhoff's Three Laws of Spectroscopy:

1. A hot solid object produces light with a continuous spectrum.
2. A hot tenuous gas produces light with spectral lines at discrete wavelengths (i.e. specific colors) which depend on the energy levels of the atoms in the gas. (See also: emission spectrum)
3. A hot solid object surrounded by a cool tenuous gas (i.e. cooler than the hot object) produces light with an almost continuous spectrum which has gaps at discrete wavelengths depending on the energy levels of the atoms in the gas. (See also: absorption spectrum)

The existence of these discrete lines was later explained by the Bohr model, which helped lead to the development of quantum mechanics.

Circuit Laws

The current entering any junction is equal to the current leaving that junction. i₁ + i₄ = i₂ + i₃

The sum of all the voltages around the loop is equal to zero. v₁ + v₂ + v₃ + v₄ = 0

Kirchhoff's circuit laws (or circuit rules) are a pair of laws that deal with the conservation of charge and energy in electrical circuits, and were first described in 1845 by Gustav Kirchhoff. Widely used in electrical engineering, they are also called Kirchhoff's rules or simply Kirchhoff's laws.

Kirchhoff's Current Law (KCL)

The current law is also called Kirchhoff's first law, Kirchhoff's point rule, Kirchhoff's junction rule, and Kirchhoff's first rule. It is based on the principle of conservation of electric charge, which implies that:

At any point in an electrical circuit where charge density is not changing in time, the sum of currents flowing toward that point is equal to the sum of currents flowing away from that point.

Kirchhoff's Voltage Law (KVL)

The voltage law is also called Kirchhoff's second law, Kirchhoff's loop rule, and Kirchhoff's second rule. It is a consequence of the principle of conservation of energy, which implies that:

The directed sum of the electrical potential differences around a circuit must be zero.

See also

• Kirchhoff equations
• Spectroscopy
• Spectrum analysis

References

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• Short biography
• John J. O'Connor and Edmund F. Robertson. Gustav Kirchhoff at the MacTutor archive
• Eric W. Weisstein, Kirchhoff, Gustav (1824-1887) at ScienceWorld.

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