[SI-LIST] FEM/BEM/MoM
- From: Abdulrahman Rafiq <arafi001@xxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 28 Aug 2003 10:36:08 -0700
Geoff,
Could you ellaborate on this a little more, as I am afraid i
can't quite see what happened to the 1/4 Joule of energy.
Perhaps if you could do a quick back of the envelope
calculation as an example.
-----------------
Just a little diversion to show the error in a schematic:
An old example often quoted is the problem of connecting two
one farad
capacitors together by a switch; one is at 1V potential, the
other zero.
The initial energy is 1/2 CV**2 =3D 0.5 joule. After closing
the switch th=
ere
is charge distribution, and energy =3D 1/8 +1/8 =3D 0.25
joule. Where did =
the
missing 0.25 joule go? If you did an electrical degree,
you'd see the
paradox. If you studied high frequencies, you'd know the
answer. (I did a
Physics degree, then built RF circuits, so for me a capacitor
is not a
capacitor.)
The answer is
1) it's not physically possible to put two capacitors
together at one point
2) therefore they are separated by a distance
3) therefore on closing the switch, the discharge current
travels a distance
4) the conductors have finite conductivity
5) therefore there is a varying electromagnetic field and
energy is
dissipated and radiated
6) please don't talk about too much about inductance because
it's only an
approximation.
-------------------
---------------------------------------
Abdulrahman Rafiq
Department of Physics
University of California
Riverside, Ca. 92521
Email: arafi001@xxxxxxx
URL: www.geocities.com/arafiq786
--------------------------------------
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