In reply to Harry Veeder's message of Mon, 12 Oct 2009 02:35:43 -0400: Hi, >Ok, I guess it is necessary to distinguish between a capacitor, a >battery and an EMF. Both a battery and a capacitor can produce a >current for a _limited_ period of time, whereas an EMF can produce a >current for an _unlimited_ period of time.
There ain't no sich animal. Nothing runs forever. The universe is a big battery, and it's running down. You can only maintain an EMF at a "constant" level, when current is flowing in a resistive circuit, by supplying energy. IOW you have to "pump" the electrons from the low voltage side back to the high voltage side. This is usually done with a changing magnetic field (i.e. a generator or dynamo), which once again introduces a step in the voltage going around the circuit. You can picture the voltage at each point as single rotation of a helix with a vertical axis with the begin and end points joined by a straight vertical line. That vertical line is where the energy is added. Energy is lost to resistance as the current runs around the helix. > >With that in mind, let me refine the question. Can a current which runs >indefinitely (and does not occur in a superconductor) be explained >consistently only with the concept of an electric field? [snip] Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/Project.html
