Re: [Phys-l] induced electric field

[John Denker <jsd@av8n.com>]

On 11/23/2009 05:54 PM, David Bowman wrote:

> The formulae I gave for E_x & E_y ought to work for both the interior
> and exterior solutions if proper care is taken.  

Yes, they do.

My bad, again.  Sorry for muddying the waters.

I have a deep-seated reflex that drives me to replace
every instance of atan(y/x) with atan2(y,x).  My gut
tells me the latter "should" always be better.  But
in this case, if I just code the formulas the way
David Bowman wrote them, with single-argument atan()
calls, the formulas work beautifully:

curl=1 expand=2 ./square-solenoid 
 0.000  0.000 -0.000 -0.000 -0.000 -0.000 -0.000  0.000  0.000 
 0.000  0.000 -0.000 -0.000 -0.000 -0.000 -0.000  0.000  0.000 
-0.000 -0.000  0.250  0.500  0.500  0.500  0.250 -0.000 -0.000 
-0.000 -0.000  0.500  1.000  1.000  1.000  0.500 -0.000 -0.000 
-0.000 -0.000  0.500  1.000  1.000  1.000  0.500 -0.000 -0.000 
-0.000 -0.000  0.500  1.000  1.000  1.000  0.500 -0.000 -0.000 
-0.000 -0.000  0.250  0.500  0.500  0.500  0.250 -0.000 -0.000 
 0.000  0.000 -0.000 -0.000 -0.000 -0.000 -0.000  0.000  0.000 
 0.000  0.000 -0.000 -0.000 -0.000 -0.000 -0.000  0.000  0.000 


I just now put up an updated (upgraded) version of
  http://www.av8n.com/physics/square-solenoid.c