Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
V and R have to refer to the same system, Rick. You are using V towant
refer to the voltage or potential across the entire distribution system,
but R to refer to the resistance of only the wires. You have to make a
choice that matches V and R appropriately, such as:
(1) V is the voltage or potential across the source of the entire
distribution system, and R is the total resistance of that system
(wires, loads, etc).
(2) V is the voltage or potential difference between one end of a wire
and the other end, and R is the resistance of that length of wire.
(3) V is the voltage or potential across a load at the customer end of
the distribution network and R is the resistance of that load.
If you take V to be the difference in voltage or potential from one end
of the wire (or other resistance) to the other (i.e. voltage drop), then
P=V*I and P=I^2*R and P=V^2/R all refer to the power which produces the
heating in the wire.
Best wishes,
Larry
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright <exit60@cablespeed.com>
Retired (June 2001) Physics Teacher
Charlotte MI 48813 USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Rick Tarara wrote:
----- Original Message -----
From: "John S. Denker" <jsd@MONMOUTH.COM>
Justin Parke wrote:
Does anyone have any notes written
about the distinction between P=VI and P=I^2R?
In an ohmic situation, there is no distinction.
In a non-ohmic situation, P=VI is exact and
I2^R has no physical significance.
I understand that the latter refers to
"joule heating loss" but I don't feel clear as to why.
P=IV is the Joule heating.
Anything else is an approximation at best.
I guess I don't understand the last part here. A specific example: I
atto supply a small town with electrical power. I need to supply
approximately 10 MW. I could try and do that at 100,000 V and 100 A, or
whatever100 V and 100,000 A. In both cases P = IV = 10MW. However, for
the resistance of the wires delivering the power, I^2R will be quite
different.
Rick
**********************************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556
rtarara@saintmarys.edu
FREE PHYSICS INSTRUCTIONAL SOFTWARE
www.saintmarys.edu/~rtarara/software.html
PC and MAC software
NEW! SIMLAB2001--DYNAMIC CARTS now available.
CD-ROMs now available
******************************************************