Re: Solving field equations in Excel

["John S. Denker" <jsd@MONMOUTH.COM>]

I wrote:
> > ... Farther right is a third grid that calculates the charge
> > density (charge per unit volume). In D=2, charge per unit
> > volume means the same thing as charge per unit area. ...

Then at 02:04 AM 2/11/01 -0500, Ludwik Kowalski wondered:
> Up to this time I was thinking and calculating distributions
> of sigma only in terms of surface charge densities (C/m^2).
> My understanding of the above (without checking it numerically
> with numbers in previous grids) was that numbers are charges
> per unit area along the infinitely long rods. These areas are
> perpendicular to the screen. The numbers are facing us but
> charges to which they refer reside in planes perpendicular
> to the screen.

Sorry for the lack of clarity.

I have rewritten the passage in question to say
> > Farther right is a third grid that calculates the charge density (charge
> > per unit volume).  If you add up all the cells in a given area, you get a
> > charge per unit length.  This means length in the Z direction;  it is the
> > charge per unit length of the object rooted in the given area and
> > extending infinitely far perpendicular to the screen.

So what my charge per unit volume is dimensionally correct;  it is just the
charge per unit length, per unit area.  (Length of rods, area of
cells.)  That's how a D=3 person would describe it.  A genuine flatlander
would describe it quite differently; the laws of physics look different in
flatland and I don't have time to go into that right now.