Paul Drude

Paul Drude modeled electrical conduction in metals through mobile charge carriers undergoing repeated collisions. In the modern relaxation-time form, an electric field accelerates the carriers between momentum-randomizing events, giving electrical conductivity $\sigma =n{e}^2\tau /m$. Here $n$ is carrier number density, $\tau$ a momentum-relaxation time and $m$ the carrier mass. The Drude model makes a useful connection between microscopic scattering and macroscopic resistance, while its classical statistics cannot explain every thermal or electronic property of a metal.^[ref]