From QuistO@mg.sdstate.edu Sat Nov 16 15:13:06 1996 Date: Tue, 17 Oct 95 09:53:00 PDT From: "Quist, Oren Phys" To: billbeskimo.com, Phys-L mail list Subject: Re: your mail ------------------------------------------------------------------------------ REPLY FROM: Quist, Oren Phys Return-Path: On Fri. 13 Oct 1995 Bill Beaty Wrote: > Very interesting! All the sources I've encountered state that each atom > in a conductor contributes one (or two?) electrons to the conduction band. > Might you know a rough figure for the actual number of electrons/atom in > a copper lattice? How much smaller is it than 1.0? The number of electrons in the conduction band is indeed as you say. But, that is not what I was saying (below). The actual number of electrons which contribute to the electrical current is not equal to the number of electrons in the conduction band. The electrons which contribute to electrical conduction are those electrons within the Fermi Surface which are "uncompensated." From symmetry, these electrons lie on, or near the surface, and result as the Fermi Surface is "shifted" by the electric field. The fraction of electrons that remain uncompensated is approximately given by the ratio (drift velocity)/(Fermi velocity). The result is the number of electrons which produce an observed current being considerably less than Avagadro's number. The number of electrons producing current being thus reduced, produces an increase in their average velocity. Average electron velocities are more probably in the meters/sec range rather than the 10ths of a millimeter/sec as is predicted by the free-electron theory. > On Fri, 13 Oct 1995, Quist, Oren Phys wrote: >> regarding the discussion about the speed of the charges and speed of the >> fields in a conductor: >> It was mentioned that the drift speed of the electrons in a conductor >is >> very small -- however, this is based on the "free-electron" model of >> conduction -- which is not correct. >> >> The actual number of electrons contributing to the conduction process >is >> related to the number of electrons on the Fermi Surface which is much, much >> smaller than avagadro's number, and the electron's resulting velocity is >much >> greater than what one gets from the free electron model. The resulting >> electronic velocity is still considerably less than the speed of light. >> >> Oren Quist Quisto@mg.sdstate.edu >> SDSU >> > >.....................uuuu / oo \ uuuu........,............................. > William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623 > EE/Programmer/Science exhibit designer http://amasci.com/ > Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page