I usually express it as a statement something like this:
The product of the voltage across any segment of a circuit and the current
in the same segment represents the rate at which the energy of the charge
carriers is being increased or decreased as they pass through that segment.
(But maybe this is too general, and someone can cite a counterexample.) I
use this for sources, resistors, capacitors, inductors, whole circuit
branches, etc. If the segment happens to be an ordinary conductor
(resistor) whose behavior is described by "Ohm's law", then V=IR and the
rate at which the energy of the charge carriers decreases (and at which the
thermal energy of the segment increases -- which I would tend to call "Joule
heating") can also be expressed as (I^2)R or (v^2)/R.
_______________________________________
Fred Lemmerhirt
Waubonsee Community College
Sugar Grove, Illinois
<mailto: flemmerhirt@mail.wcc.cc.il.us> http://chat.wcc.cc.il.us/~flemmerh/physics.html
-----Original Message-----
From: Justin Parke [mailto:FIZIX29@AOL.COM]
Sent: Wednesday, February 20, 2002 1:28 PM
To: PHYS-L@lists.nau.edu
Subject: electrical power
Does anyone have any notes written about the distinction between P=VI and
P=I^2R? I understand that the latter refers to "joule heating loss" but I
don't feel clear as to why.