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Re: point particles



Dear All,
Dan Crowe is correct of course. Feynman Lectures II
also discusses similar distributions but you got to read
between the lines a little. Now in a quantum mechanical
scattering problem between two electrons or an electron
and a nucleus, the energy and momentum that matters is
always referenced to the center of mass of the collision
which is referenced to the center of mass of each object.
If the electrical charge distribution causing the
scattering is not centered at the center of mass of the
object, namely the electron, then there will be a
scattering amplitude or cross section resulting from the
electron as if it had a dipole moment. This has been
looked for experimentally and probably has some upper
limit, but I don't know what it is.

I am off to the AAPT meeting in MIAMI and will not be able
to communicate until my talk is done.

Regards,
Richard Lindgren




On Wed, 21 Jan 2004 17:36:53 -0500
Ludwik Kowalski <kowalskil@MAIL.MONTCLAIR.EDU> wrote:
On Wednesday, Jan 21, 2004, at 17:00 America/New_York,
Dan Crowe wrote:

A multipole expansion can be calculated for any charge
distribution, including a single point charge. The
multipole expansion is calculated relative to a
particular
coordinate system. If a point charge is not at the
origin,
the dipole moment, relative to the coordinate system, is
nonzero. See, for example, Eyges or Jackson.

Are you saying that the magnitude of the dipole
moment of a "system" can have any value,
depending on where the origin of our coordinate
system is? I was under the impression that the
dipole moment is a system property, like its total
mass or charge. Is this wrong?
Ludwik Kowalski