MadSci Network: Physics
Query:

Subject: Static EM fields and momentum

Date: Fri Dec 10 14:07:09 2004
Posted by Ryan
Grade level: undergrad School: No school entered.
City: No city entered. State/Province: No state entered. Country: No country entered.
Area of science: Physics
ID: 1102709229.Ph
Message:

In a previous question, Dr. Jerrold Franklin stated that Static EM fields can 
exert no force (http://www.madsci.org/cgi-
bin/circR?/posts/1102435169.Ph.r.html).  The equation for force in a volume 
from "Introduction to Electrodynamics", Griffiths, 3rd ed.
is written in terms of the surface integral of the Maxwell Stress Tensor + d/dt
(Volume integral of Poynting vector).
Clearly, in the static case, the 2nd term drops out, and F=SurfaceIntegral
[Maxwell Stress Tensor].
This is a non-zero quantity in general, so in general, static fields can exert 
force.  Doesn't this contradict the Dr. Franklin's previous answer?


Re: Static EM fields and momentum

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