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Re: point particles



Look at:
http://physicsweb.org/article/news/6/2/13

These experiments are seeking to measure the dipole moment of the electron
relative to its CM.

The article states:
"The electron's electric dipole moment is a measure of the average distance
of charge from the electron's centre of mass."

This is an instance where people in a specific specialty usurp established
terminology and customize it as if it applies to only their specialized
application.
Well established textbook definitions should be respected by researchers.
Let us not compound the students' sources of confusion.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.velocity.net/~trebor/
trebor@velocity.net
----- Original Message -----
From: "Bob Sciamanda" <trebor@VELOCITY.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, January 22, 2004 1:15 PM
Subject: Re: point particles


Ludwik,
I don't know who made that claim, but the dipole moment of a non neutral
charge distribution is defined only relative to an origin. Perhaps an
assumed origin was embedded in the context of the discussion(?).
.
P.S.: J Denker's specification of the CM as the assumed origin for the
"physics" dipole moment is news to me. In my experience no mention of the
CM occurs in any textbook definition of the physics electrical dipole
moment. John, would you give a reference for this distinction between a
"mathematical" vs "physics" dipole moment?

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.velocity.net/~trebor/
trebor@velocity.net
----- Original Message -----
From: "Ludwik Kowalski" <kowalskil@MAIL.MONTCLAIR.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, January 22, 2004 1:00 PM
Subject: Re: point particles


Yes, but the claim was made that the
dipole moment of a point charge (NOT
Q=0) is an intrinsic property of the object
in which that point charge is located. By
"intrinsic" I mean "not dependent of the
location of the reference point. How this
can such claim be justified?
Ludwik Kowalski



On Thursday, January 22, 2004, at 12:18 PM, Bob Sciamanda wrote:

Huh? The center of mass location has nothing to do with the electrical
dipole moment, the dipole moment is calculable from only a knowledge
of
the charge distribution.

In answer to another, related query, the dipole moment of a charge
distribution is in general dependent upon one's choice of origin for
the
calculation. But if the monopole moment is zero (overall electrical
neutrality) the dipole moment is independent of the choice of origin.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.velocity.net/~trebor/
trebor@velocity.net
----- Original Message -----
From: "Richard A. Lindgren" <ral5q@VIRGINIA.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, January 21, 2004 3:44 PM
Subject: Re: point particles


. . .
If the electron had a slight displacement of its center of
mass to its center of charge, it would have what is called
an electric dipole moment. . . .