Gustav Robert Kirchhoff

German physicist

German theoretical physicist Gustav Robert Kirchhoff developed a series of physical laws that synthesized knowledge in different fields of physics, including thermodynamics and optics. With Robert Bunsen, Kirchhoff carried out experiments that founded the field of spectroscopy.

Born: March 12, 1824; Königsberg, Prussia (now Kaliningrad, Russia)

Died:October 17, 1887; Berlin, German Empire

Primary field: Physics

Specialties: Theoretical physics; optics; electromagnetism; thermodynamics

Early Life

Gustav Robert Kirchhoff was born in Königsberg, then a city of the Kingdom of Prussia, on March 12, 1824. His father, Carl Friedrich Kirchhoff, was a Prussian law councillor and county judge. His mother, Johanna Henriette, was a homemaker. Kirchhoff was the youngest of three brothers.

Kirchhoff graduated from high school in 1842 and enrolled in the University of Königsberg, intending to study mathematics. At the university, Kirchhoff attended the lectures of noted mathematician Friedrich Julius Richelot, but he was particularly influenced by the physicist Franz Ernst Neumann, who encouraged Kirchhoff to study physics. Kirchhoff’s mathematical talent served him well in the developing field of mathematical physics.

Kirchhoff published his first scientific paper in 1845, while still a student. The paper articulates a series of laws for calculating the values (such as currents, voltages, and resistances) of electric currents. Kirchhoff discovered these laws while performing practical experiments in Neumann’s laboratory. For theoretical background, Kirchhoff built on the work of German physicist Georg Simon Ohm. On the basis of this research, Kirchhoff received his doctorate from the University of Königsberg in 1847.

Kirchhoff’s doctoral dissertation earned him a fellowship to study in another city. He initially planned to travel to Paris, France; however, because of political upheaval occurring in France, Kirchhoff instead settled in Berlin. In 1848, Kirchhoff passed his state doctoral exams, which permitted him to teach students in the German university system, and carried out further work on the effect of Ohm’s law on currency and resistors in electric circuits.

Life’s Work

In 1850, Kirchhoff was appointed extraordinary professor of experimental physics at the University of Breslau (now Wroclaw, Poland). He proved talented in conducting physical experiments. Based on his experimental results, Kirchhoff modified the theory of elasticity, eliminating some erroneous assumptions made by the theory’s founder, French physicist Siméon Denis Poisson. Kirchhoff’s skill with experiments quickly earned him the admiration and lifelong friendship of German chemist Robert Bunsen. From 1851 to 1852, Bunsen was a professor at Breslau. After Bunsen accepted a professorship at the University of Heidelberg in 1852, he persuaded Heidelberg’s faculty to offer Kirchhoff the position of professor of physics. Kirchhoff accepted gladly and moved to Heidelberg in 1854. In 1857, Kirchhoff married Clara Richelot, the daughter of his former mathematics professor, with whom he would have several children.

That same year, based on his theoretical calculations, Kirchhoff proposed that the speed of an electric impulse traveling across an ideal wire without resistance would be that of the speed of light. Turning toward the field that would later be called thermodynamics, in 1858, Kirchhoff developed his law of thermochemistry. This law states that the heat of a chemical reaction is determined by the difference in heat capacity (the amount of heat necessary to change the temperature of a substance) between products and reactants.

In 1858, Kirchhoff began a scientific collaboration with Bunsen that culminated in their development of spectroscopy. They built their own spectroscope, and in 1859, Kirchhoff and Bunsen compared the spectrum of sodium chloride vapors with the spectrum of sunlight. This led them to the discovery that spectral analysis of light emitted from a particular source could be used to determine the chemical composition of that source. They published their findings in 1860. That year, Kirchhoff and Bunsen discovered the element cesium by spectroanalysis of local mineral water. In 1861, they discovered rubidium by the same method.

A direct result of Kirchhoff and Bunsen’s development of spectroanalysis was Kirchhoff’s initial proposal of his law of thermal radiation in 1859. Reiterated in 1860 and reformulated in its final version in 1862, this law states that for any body that emits and absorbs thermal electromagnetic radiation in thermal equilibrium, the ratio of its emission to its absorption is determined by the wavelength and temperature of its radiation. In 1862, Kirchhoff termed this ideal body a “blackbody”; the radiation that it emits and absorbs is “blackbody radiation.”

For his analysis of the solar spectrum and the attendant discovery that when light passes through a gas, the spectral lines emitted by the gas absorb the same lines in the spectrum of the original light, leading to the appearance of dark lines in their place, Kirchhoff was awarded the prestigious Rumsford Medal in 1862. That year, Kirchhoff and Bunsen traveled to England upon the invitation of English chemist Henry Enfield Roscoe. Returning to Heidelberg, Kirchhoff focused on theoretical physics. A foot injury led Kirchhoff to concentrate further on theoretical areas of inquiry, as performing experiments became more difficult.

His wife, Clara, died in 1869, and Kirchhoff married Luise Brömmel, a nurse, three years later. In 1875, Kirchhoff accepted the position of professor of mathematical physics at the University of Berlin. While in Berlin, Kirchhoff developed what would be called the Kirchhoff equations. The series of equations describes mathematically the parameter of how a rigid body moves through the medium of an ideal fluid, a fluid that has no viscosity and cannot be compressed.

Kirchhoff continued to teach at the University of Berlin until 1886. He died in Berlin on the morning of October 17, 1887.

Impact

Kirchhoff’s aptitude in theoretical physics led him to discover natural laws in many fields of physics, ranging from electromagnetism to spectroscopy to thermodynamics. He was able to synthesize and order many of the empirically based physical advances made previously and develop new laws from his own physical experiments. His collaboration with Robert Bunsen served as model of scientific teamwork, and his discoveries built a foundation from which the next generation of physicists examined both the smallest structure of matter and the composition of distant stellar bodies. Kirchhoff’s combination of theoretical and experimental physics led to major advances and inspired further research in numerous fields.

The physical laws discovered and articulated by Kirchhoff have retained their validity and scientific importance. Kirchhoff’s law of thermal radiation and his related three laws of spectroscopy proved invaluable for both the field of astrophysics and the development of quantum mechanics by German physicist Max Planck and others. These laws enabled, through spectroscopy, the first analysis of the chemical composition of celestial bodies. Kirchhoff’s work on blackbodies and blackbody radiation influenced the work of future generations of astrophysicists. In electrical engineering, Kirchhoff’s laws related to current and voltage have become important analytical tools and been incorporated into software applications. Kirchhoff’s law of thermochemistry permits calculation of the heat generated by chemical reactions at different temperatures, an issue of importance in physical chemistry and with practical applications in industry.

Bibliography

Ball, David W. The Basics of Spectroscopy. Bellingham: SPIE, 2001. Print. Describes Kirchhoff and Bunsen’s groundbreaking work, which laid the foundations for twenty-first-century spectroscopy.

Bartusiak, Marcia. “Deciphering the Solar Spectrum.” Archives of the Universe: 100 Discoveries That Transformed Our Understanding of the Cosmos. Ed. Marcia Bartusiak. New York: Vintage, 2006. 211–17. Print. Provides an outline of the contribution of Kirchhoff and Bunsen to the development of spectroscopy as applied to analyzing the composition of the light of the sun.

Huebener, Rudolf P., and Heinz Luebbig. A Focus of Discoveries. 2nd ed. Hackensack: World Scientific, 2012. Print. Surveys the contribution of Kirchhoff’s discoveries to the development of quantum theory.

Jammer, Max. Concepts of Force. 1957. Mineola: Dover, 2011. Print. Describes Kirchhoff’s opposition to the concept of force in physics and provides a look at his view on the nature of science.