[SI-LIST] Re: Circle bus topology; Circular Firing Squad?
- From: olaney@xxxxxxxx
- To: david.banas@xxxxxxxxxx
- Date: Thu, 2 Aug 2007 15:19:19 -0700
OK, thanks for the clarification. Yes, the EM field is happy in free
space, but the finite penetration into the metal, completely for DC, and
increasingly less so for AC as frequency rises, is the physical current
flow that supports the external EM field (speaking of the PC trace as the
EM source rather than as a receiving antenna). Perhaps you could
rephrase the spring model more accurately, and it would be appreciated,
but the essence of the matter seems unchanged. Here is a description of
metal from the wikipedia article on plasmons: "Plasmons are explained in
the classical picture using the Drude model of metals. The metal is
treated as a three dimensional crystal of positively charged ions, and a
delocalized electron gas is moving in a periodic potential of this ion
grid." Even the Drude model is just an approximation. This is simply
deeper into the physics than is needed for this crowd. I tried to
simplify it. Sorry if it fell short for you, and I'm glad you chimed in.
Orin
On Thu, 2 Aug 2007 14:43:48 -0700 "David Banas" <david.banas@xxxxxxxxxx>
writes:
> Sorry to fuel this, but there're a few corrections that need to be
> made
> here...
>
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On Behalf Of olaney@xxxxxxxx
> > Sent: Wednesday, August 01, 2007 2:16 PM
> > To: Arpad_Muranyi@xxxxxxxxxx
> > Cc: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Circle bus topology; Circular Firing Squad?
> >=20
> > I've added an additional note to forestall a dead end line of
> reasoning.
> > You are headed in the right direction. The electrons only drift
> slowly
> > with the current. Meanwhile, they wander all over the place under
> > thermal influence. Note that being electrons, they mutually repel
> and
> > never actually collide.
> [David Banas] This statement conveys the notion that there is an
> exact
> boundary between particle locations, which must be crossed, in order
> for
> a "collision" to have occurred. This is not a physically correct
> interpretation. After all, we know that particles can be accurately
> described by wave functions that have exponentially decaying
> amplitudes,
> which never go completely to zero. That is, there is a small but
> finite
> probability for every particle to "be" anywhere. Therefore, one
> could
> argue that all particles are "colliding" all the time.
>
> >To do that, electrons require energies typical
> > of a particle accelerator. The temperature would have to be so
> high
> that
> > the metal would have long since vaporized.
> >=20
> > For solid metals at room temperature (and considerably higher),
> the
> sea
> > of electrons in the metal acts like a 3D mesh of tiny masses
> suspended
> by
> > electrostatic "springs". The wave is transmitted at close to the
> speed
> > of light by the electrostatic forces in the mesh (action at a
> distance).
> [David Banas] No, E&M waves require no medium in which to propagate.
> They are perfectly happy propagating through free space. In fact,
> just
> the opposite of what you posit is true; it is very difficult for an
> E&M
> wave to propagate very far into a conductor.
>
> > The response of the mesh to disturbances is linear and
> superposition
> > applies.
> [David Banas] Actually, atomically bound electrons also exhibit some
> non-linear characteristics in their response to electromagnetic
> field
> perturbances. They are very small compared to the linear component
> of
> the response, but they are NOT zero.
>
> Waves can pass in all directions simultaneously and
> > independently.
> >=20
> > Note: The electric wave propagation is so fast compared to the
> electron
> > drift, that though the electrons will wiggle slightly in response,
> their
> > nominal positions are as if they are frozen in a snapshot. Drift
> > movement is of no consequence to the wave propagation.
> [David Banas] You need to be careful here. If by "drift movement"
> you
> mean the d.c. component of the current in the conductor induced by
> the
> incident electromagnetic field, then I agree with you. However, that
> induced current also has a.c. components (which I think might be
> what
> you're referring to when you say "wiggling"), and those a.c.
> components
> very much affect the electromagnetic field, both near to and far
> from
> the conductor. (After all, if they didn't, there'd be no difference
> between a conductor's and an insulator's effect on E&M fields,
> right?)
>
> The thermal
> > portion averages to zero, and the slow drift with current is a
> response,
> > not a cause.
> [David Banas] It's actually both. For instance, there will
> definitely be
> a magnetic field generated around the conductor by this current,
> which
> would not be generated if the E&M field were incident upon an
> insulator.
>
> >=20
> > Orin
> >=20
> >=20
> >=20
> > On Wed, 1 Aug 2007 12:03:15 -0700 "Muranyi, Arpad"
> > <Arpad_Muranyi@xxxxxxxxxx> writes:
> > > Now that I think of it, the electrons in the copper lattice
> > > are moving in all different directions, not just in the
> > > direction of the wave, so they not only hit the electrons
> > > of the other wave where the waves meet, but they also hit the
> > > electrons of their own wave... So the bouncing will basically
> > > follow a random pattern allowing some to go through, some
> > > go sideways, others to turn around, etc...
> > > =3D20
> > > Arpad
> > >
> > > -----Original Message-----
> > > From: Muranyi, Arpad=3D20
> > > Sent: Wednesday, August 01, 2007 11:13 AM
> > > To: si-list@xxxxxxxxxxxxx
> > > Subject: RE: [SI-LIST] Re: Circle bus topology; Circular Firing
> > > Squad?
> > >
> > > This is why we need to use coloring dye... :-)
> > >
> > > Seriously, I wonder about the particle and
> > > wave duality of electrons. Remember, the
> > > drift velocity of electrons is not the same
> > > as the propagation velocity of the EM waves.
> > >
> > > So what happens at the "collision" point (i.e.
> > > the electrical midpoint of the loop)? Do=3D20
> > > the electrons hit each other and bounce back
> > > like balls with the drift velocity speeds,
> > > while at the same time the waves go through
> > > each other (at speeds close to c) without
> > > changing directions?
> > >
> > > Another analogy comes to my mind, when two laser
> > > beams on different path cross each other. After
> > > the cross point we are still going to see their
> > > original colors without any mixing. However,
> > > if you did the same with two water streams,
> > > the cross point will result in a splash in all
> > > different directions...
> > >
> > > Is there someone out there with a good physics=3D20
> > > background who could shed some light on this?
> > >
> > > Thanks,
> > >
> > > Arpad
> >=20
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