Re: [Phys-l] Thermal heating in a resistor?

["John Clement" <clement@hal-pc.org>]

> Why is the formula P=I^2V used to describe thermal power loss in resistor
> instead of P=IV or P=V^2/R? Is this just the textbook author's choice of
> formula?
> -Tony
> --
> Tony Wayne
> Albemarle High School
> Physics Teacher
> Science Department Chair
> twayne@k12albemarle.org
> http://www.mrwaynesclass.com

I have just come across an extremely likely explanation for this usage.
This is called the Joule-Lenz law or Joule's first law.  This historical
usage may have influenced the textbook writer.  Often laws are presented in
a historical fashion, rather than in a fashion that might allow students to
make sense of it.

Hence the most unfortunate use of the terms action and reaction which are
historical terms.  I say unfortunate because they bring up pictures of
motion rather than forces in student's minds.  The simplistic linking in the
statement "action equals reaction" is a mantra that students easily repeat
without thinking about what it really means.

I had never heard of this law, probably because textbooks ignore the name.
However reading a little Kuhn caused it to pop up.  There is a short
Wikipedia article on it, and it was found experimentally.

John M. Clement
Houston, TX