|MadSci Network: Physics|
Dear Jordan, The conductivity for a material, such as a semiconductor, can be expressed as¡K sigma = q*n*m Where, m = u/Ea = electron mobility (cm^2/Vs) n = electron charge q = average number density u = average electron velocity (cm/s) Ea = applied electric field (V/cm) The resistivity, R, as you probably know, is inversely proportional to the conductivity, sigma, such that... R= L/(sigma*A) Where, L= length of the material (cm) A= cross-sectional area of the material (cm^2) In a collisionless plasma, the resistivity was previously believed to be due to particle scattering by unstable acoustic waves driven by applied electric and magnetic fields. In fact, clumps of electrons and ions form apparently in these acoustically-driven plasmas. These clumps act as if they were single particles ¡V ¡§macroparticles¡¨! These macroparticles then collide and scatter from one another. This adds a dynamic dragging factor to the conductivity of the plasma, so that¡K sigma = q*n*un/(-Edrag) = q*n*un/(E0) (units of cm^-1*ohm^-1) Where, E0= -Edrag(electron ¡§drag¡¨) (V/cm) The calculation of the electron "drag" in an active plasma is a complex affair, beyond the mathematical tools you have been equipped with in 10- 12 grade. Hope this help, ---* Dr. Ken Beck
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