Paul Drude
Who Made the Metal a Gas · Physicist · 1863–1906
Who in 1900 treated the free electrons in a metal as a gas wandering between fixed positive ions, and got out of that single picture both the electrical and the thermal conductivity of metals — and a ratio between them that matched a measurement made fifty years earlier.
Who was Drude?
Paul Drude was born in Brunswick in 1863 and studied at Göttingen under Woldemar Voigt, beginning in mathematics and turning to physics. His early work was in optics, and his textbook on the subject was widely used; he is also the reason the speed of light is written c. In 1900, three years after J. J. Thomson had identified the electron, Drude published in the Annalen der Physik a theory of the metals built on one bold simplification. Take the electrons that Thomson had found and suppose that in a metal a certain number of them are free — not attached to any particular atom — and that they move through the metal exactly as the molecules of a gas move through a box. What is left behind is a rigid framework of heavy positive ions, fixed in place, and the electrons collide with these as gas molecules collide with obstacles. Apply an electric field and the electron gas drifts: that drift is the electric current, and the collisions are what we call resistance. Heat one end of the bar and the same electrons carry energy to the other end: that is thermal conduction. The persuasive part was not either result on its own but the ratio between them. Divide the thermal conductivity by the electrical and most of the properties of the electron cancel, leaving a quantity that depends only on the temperature and on constants — and the number that came out was close to the ratio Rudolph Franz and Georg Wiedemann had measured empirically in 1853, without any theory at all. Drude became editor of the Annalen der Physik in 1900, a position of great influence in German physics, and was appointed to a chair at Berlin in 1905. He died the following year. His model was superseded by the quantum theory of solids, which explained the things it could not, and it is still taught, because the picture of a metal as a lattice of positive ions in a sea of mobile electrons is his.
Major achievements
- Published the free-electron theory of metals in 1900, three years after the electron was identified
- Explained electrical conduction in a metal as the drift of a gas of free electrons
- Explained thermal conduction in a metal by the same carriers
- Derived the ratio of thermal to electrical conductivity and reproduced the Wiedemann–Franz value of 1853
- Introduced the symbol c for the speed of light
Life in brief
- 1863 — Born at Brunswick: Son of a physician.
- 1887 — Doctorate at Göttingen: Under Voigt, on optics.
- 1894 — The letter c: Adopts the symbol for the speed of light.
- 1900 — The electron gas: The free-electron theory of metals.
- 1900 — Editor of the Annalen: The most influential physics journal in Germany.
- 1905 — Chair at Berlin: Brought in by Planck.
- 1906 — Dies at Berlin: Aged forty-two.
Explore the life of Drude — five chapters
- Göttingen, and the Letter c — From mathematics to optics
- A Metal Is a Box of Gas — The free-electron model, 1900
- The Ratio — Reproducing a number measured forty-seven years earlier
- What It Cannot Do — A heat capacity metals do not have
- Forty-Two — The Annalen, a chair at Berlin, and a death nobody explained
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