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# Thermodynamics of Electricity

## Thermodynamics of Electricity - Physics Forum

### Thermodynamics of Electricity - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

#11
01-29-2004, 11:46 PM
Thermodynamics of Electricity

"The Void" <[Only registered users see links. ]> wrote in message

I must have been half-asleep when I first saw this post, otherwise I would
have stopped it *here* to reply.

The square of the electric field strength E is proportional to the energy
*DENSITY* u(E) in the electric field:

u(E) = (1/2)*k*e0*E^2

where k is the dielectric constant and e0 is the permittivity of free space.

Energy density u is energy U per unit volume V.

u = dU/dV

There is absolutely no reason why this should be so.

Maxwell developed the equipartition theorem to describe the distribution of
kinetic energy in a hard-sphere model of an ideal gas. To extend this
principle to E-M one must also consider that there is energy storage in
*magnetic fields*. The energy density due to the magnetic field u(B) is
proportional to the square of the magnetic field strength B

u(B) = (1/2)*B^2/mu0

where mu0 is the permittivity of free space.

This energy storage is independent of the energy storage in the electric
field, but both coexist in the same space and time.

u(tot) = u(E) + u(B)

Since each field has three vector components:

u(E) = u(E(x)) + u(E(y)) + u(E(z))
u(B) = u(B(x)) + u(B(y)) + u(B(z)),

so

u(tot) = u(E(x)) + u(E(y)) + u(E(z)) + u(B(x)) + u(B(y)) + u(B(z))

That is the analog of the equipartition theorem for E-M fields.

....equal to a differential quantity of energy dU(x). as shown above:

dV * u = dU

Tom Davidson
Richmond, VA

#12
01-30-2004, 08:25 AM
 zigoteau Guest Posts: n/a
Thermodynamics of Electricity

"Franz Heymann" <[Only registered users see links. ]> wrote in message news:<bvbuue\$15f\$[Only registered users see links. ]>...

Hi, Franz and Void,

No, I don't think so. You do come across expressions which diverge,
and you can express that as the reciprocal of an infinitesimal. Void's
calculation is not too different from the divergence of the vacuum
zero-point energy of fame.

Well, Void, did you comprehend? And anyway, Franz, what's the point of
talking down to people? Sure, the average level of Usenet is
desperate, but:

Is it just for the moment we live?
When you sort it out, Alfie?
Are we meant to take more
Than we give
Or are we meant to be kind?

Cheers,

Zigoteau.
#13
01-31-2004, 09:03 AM
 Franz Heymann Guest Posts: n/a
Thermodynamics of Electricity

"zigoteau" <[Only registered users see links. ]> wrote in message
news:<bvbuue\$15f\$[Only registered users see links. ]>...
which
which

I talk down to people only after I discover that they post wrong arguments
only in order to argue about bees in their bonnets, and prove themselves to
be unwilling to learn from the replies to their posts.

Franz

 Tags electricity , thermodynamics

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