[pstricks] pst-electricfield WITH code-example

[Doris Behrendt]

list,

within the last mail, I forgot to include the code ... so here again:
I have found some errors (concerning physics) in the package:

1.) rogue field lines: the horizontal line in picture 1 is NOT a  
normal field line, but a so called rogue field line: if you change  
posArrow=.3 to posArrow=.4, the direction of the arrow will change;  
this is physically the right behaviour, but problematic when one  
thinks of large distances where the arrow must point to the left, not  
right;

2.) the number of lines emanating from a positive charge (or  
terminating on a negative charge) is proportional to the magnitude of  
the charge [tipler/mosca, p.712], so if you look at picture no.2 and  
count the lines emanating the double positive charge, you get 16;  
following the above proportionality, there must be 8 lines terminating  
in the right charge (negative and half the magnitude of the right  
one), but there are only 7;

3.) the lines emanating from (or terminating on) an isolated charge  
are drawn uniformly spaced as they emanate (or terminate) [tipler  
again], so if you look at the pictures no.3 or no.4, this is not the  
case;


\documentclass[draft]{beamer}
\usepackage{pstricks,pst-electricfield}
\usepackage{pstricks-add}

\begin{document}

%--------------------------------------------------------------
\begin{frame}
%\psset{unit=.5cm}
\scriptsize
\begin{pspicture*}(-2.5,-2)(2.5,1)
\psElectricfield[Q={[-1 -.3  0][2 .3 0 0]},%
linecolor=red,posArrow=.3,points=200,Pas=0.02,linewidth=.7pt]
\rput(-.5,-1.5){1) Nleft=default, Nright=0}
\end{pspicture*}
\begin{pspicture*}(-2.5,-2)(2.5,1)
\psElectricfield[Q={[-1 -.3  0 0][2 .3 0]},%
linecolor=red,posArrow=.4,points=200,Pas=0.02,linewidth=.7pt]
\rput(-.5,-1.5){2) Nl=0, Nr=default}
\end{pspicture*}
\begin{pspicture*}(-2.5,-2)(2.5,1)
\psElectricfield[Q={[-.7 -.3  0][1.4 .3 0]},%
linecolor=red,posArrow=.4,points=200,Pas=0.02,linewidth=.7pt]
\rput(-.5,-1.5){3) Nl=Nr=default}
\end{pspicture*}
\begin{pspicture*}(-2.5,-2)(2.5,1)
\psElectricfield[Q={[-.7 -.3  0 6][1.4 .3 0 11]},%
linecolor=red,posArrow=.4,points=200,Pas=0.02,linewidth=.7pt]
\rput(-.5,-1.5){4) Nl=6, Nr=11}
\end{pspicture*}
\end{frame}
\end{document}