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## Wiedemann-Franz lawIn physics, the ## Additional recommended knowledgeTheoretically, the proportionality constant - .
This empirical law is named after Gustav Wiedemann and Rudolf Franz, who in 1853 reported that Qualitatively, this relationship is based upon the fact that the heat and electrical transport both involve the free electrons in the metal. The thermal conductivity increases with the average particle velocity since this increases the forward transport of energy. The electrical conductivity, on the other hand, decreases while particle velocity increases because the collisions divert the electrons from forward transport of charge. The mathematical expression of the law can be derived as following.
Electrical conduction of metals is a well known phenomenon and is attributed to the rather free conduction electrons. It is measured as sketched in the figure. The current density Drude (around the year 1900) realized that the phenomenological description of conductivity can be formulated quite generally (electron-, ion-, heat- etc. conductivity). Although the phenomenological description is incorrect for conduction electrons, it can serve as a preliminary treatment. The assumption is that the electrons move freely in the solid like in an ideal gas. The force applied to the electron by the electric field leads to an acceleration according to This would lead, however, to an infinite velocity. The further assumption therefore is that the electrons bump into obstacles (like defects or phonons) once in a while which limits their free flight. This establishes an average or drift velocity ## See also |

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Wiedemann-Franz_law". A list of authors is available in Wikipedia. |