home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!ogicse!das-news.harvard.edu!husc-news.harvard.edu!husc8!mcirvin
- From: mcirvin@husc8.harvard.edu (Mcirvin)
- Newsgroups: sci.physics
- Subject: Re: Defining Photons
- Message-ID: <mcirvin.712422938@husc8>
- Date: 29 Jul 92 15:15:38 GMT
- Article-I.D.: husc8.mcirvin.712422938
- References: <3946@cruzio.santa-cruz.ca.us> <FRANL.92Jul28173419@draco.centerline.com>
- Lines: 22
- Nntp-Posting-Host: husc8.harvard.edu
-
- franl@centerline.com (Fran Litterio) writes:
-
- >I'm not an expert on the subject, but I could swear that I've heard
- >that Ohm's Law was never an exact description of reality in the first
- >place (even before QM and relativity). If so, the obvious question
- >is: Does whatever passes for the modern replacement for Ohm's Law (if
- >such exists) also lack a time parameter?
-
- It's there even in the old-fashioned version of Ohm's Law. The
- voltage-current relation is derived, with various assumptions, from
- the *local* statement E = j*rho, where E is the electric field,
- j is the current density, and rho is the resistivity, all
- evaluated at the same place and time in a material for which a
- resistivity can actually be defined. It's nonlocal to the extent
- that you're averaging over atomic phenomena and over the time
- required for transient effects to go away, but that's it.
-
- You are right: Ohm's Law was never interpreted as more than an
- approximate description of a certain class of materials.
-
- --
- Matt McIrvin mcirvin@husc.harvard.edu
-