On Tue, 02 Aug 2005 22:01:40 GMT, "daestrom" Gave us:
Since a thin round copper wire has a very low emissivity it wont give up its heat all that fast. This will mean that your thermal gradient won't be as prevalent as you suggest. The proof is when one takes a copper wire and places it across a battery's terminals. Notice how the entire wire turns a nice cherry red quite evenly, all the way up to where it is attached to any form of sinking element.
The current throughout the wire will be even, and it is that current which generates the heat, or more precisely, the resistance to said current flow.
If the wire were giving up its heat real fast, like that of a finned heat sink with air passing over it, I might agree. In the case of bare copper, however, the temperature throughout the wire is going to be very even. Your gradient will be nearly undetectable.
For a very large diameter copper bus, it MIGHT have a slight gradient between the center and the outer surface, but not much. For wire, it is as even as even gets.