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# Re: [Phys-l] Poynting Vector

but - - - - -

The Poynting vector is non-zero only within the capacitor nicht whar?

But the space filling Vector Potential (A?) doesn't give a hoot about the charged capacitor (or does it??) (I'll wager it DOES)

Would Feynmann's solenoid rotate if there were no charge in the picture?

(GAD - Corson & Lorain was a LOOOOOOONG time ago)

On Jun 30, 2008, at Jun 30(Mon) 1:12 , John Denker wrote:

On 06/30/2008 09:47 AM, chuck britton wrote:
If I remember correctly, Feynmann related the angular momentum to the
'Vector Potential' of the B field.

It's *all* related. You can't have a vector potential without
having a B-field somewhere, and vice versa. You can express the
physics in terms of A or in terms of B; the words are different
but the physics is the same.

This makes it independent of the Poynting Vector??

No, not independent. It's *all* related.

I'm thinking it might be related to the 'flow' of energy in the
capacitor.

Sure. It's *all* related.

In this case, the relationship can be understood in terms of the
symmetry of the stress-energy tensor. (See previous note.) In
particular,
a) the top row T(0,...) is the same as
b) the left column T(...,0).

The point is that
a) the spacelike part of the left column represents the energy
flowing in the x,y,z directions.
b) the spacelike part of the top row represents momentum in the
x,y,z directions that doesn't flow anywhere in space; it just
sits there in space. (You can say it "flows" toward the future,
if you want to take a four-dimensional view of the situation).

Bottom line: Yes, the energy-flow is related to the momentum.
"Related" as in "identical" (up to meaningless factors of c).

Reference: Electromagnetic stress-energy tensor:
http://en.wikipedia.org/wiki/Electromagnetic_stress-energy_tensor

Reference: Conservative flow in spacetime:
http://www.av8n.com/physics/conservative-flow.htm

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