Re: [femm] BELA electrostatic force calc

["iaaeinc" <iaaeinc@xxxxxxxxx>]

>Equation (9) should have be:
>
>df = (1/2)(D*(E.n)+E*(D.n)-(D.E)*n)

I still have some doubt about this equ :)

>From a pure mechanicl POV, Since the charge only exists on the 
conductor surface, so the traction/stress due to the conductor 
surface charge in such E filed is the surface integral of Maxwell 
stress tensor Tij

SurfInt{Tij*n(dS)}

As far as why this is the same for a closed surface path, it is just 
the Gauss divergence manipulation,

VolInt{F(dV)} = VolInt{Div(Tij)(dV)} = CloseSurfaceInt{Tij*n(dS)}

since the force is the divergence of the traction (Maxwell stress 
tensor in this case). However, this is from the POV that the electric 
charge is assume to be eps*E everywhere - but make no sense since 
there is no actual charge in the dielectric media or the conductor. 
It just explains why the number is the same for any closed surface 
path.

I guess this is only important if you want to subsequently apply the 
force to the conductor.

ted