# [pstricks] Re : Elektrostatic Field and equipotentiallines

Herbert Voss Herbert.Voss at FU-Berlin.DE
Tue Jan 19 20:06:48 CET 2010

Am 18.01.2010 21:32, schrieb Thomas Söll:

> ist possible to draw an equipotentialline in your solution of the
> fildlines through an given point?

also with Manuels solution. But I do not understand
why the V lines are far away from the charges?

Herbert

\documentclass{article}
\makeatletter
\let\ScreenCoor\tx at ScreenCoor
\makeatother
\def\FieldLines{
0 1 NoQ { /i ED xP i getX sub yP i getY sub Pyth } for
0 0
0 1 NoQ { /i ED
i getQ xP i getX sub mul i getR 3 exp Div add exch
i getQ yP i getY sub mul i getR 3 exp Div add exch
} for
/Ex ED  /Ey ED
/NormeE Ex Ey Pyth def
/dX Ex NormeE div pasX mul def
/dY Ey NormeE div pasX mul def
}

\begin{document}

\def\NoQ{4}
\def\dAngle{18}
\def\Qcharge{ 1 1 1 1}
\def\Xcoor{ -2.5  2.5 2.5 -2.5}
\def\Ycoor{ -2.5 -2.5 2.5  2.5}

\pstVerb{
/xmin -5 def /xmax 5 def /ymin -5 def /ymax 5 def
/pasX xmax xmin sub 200 div def % 0.05
/NoQ \NoQ\space 1 sub def
/Qcharge [\Qcharge] def
/Xcoor [\Xcoor] def
/Ycoor [\Ycoor] def
/getX { Xcoor exch get } def
/getY { Ycoor exch get } def
/getQ { Qcharge exch get } def
/getR { Radius exch get } def
}
\begin{center}
\begin{pspicture*}(-5,-5)(5,5)
\multido{\iB=0+1}{\NoQ}{%
\psforeach{\iA}{0,10,..,360}{%
\psparametricplot[plotpoints=2000]{xmin}{xmax}[{
/xStart \iB\space getX  def
/yStart \iB\space getY def
/pasX  \iB\space getQ dup abs Div 0.05 mul def
/xP xStart pasX \iA\space cos mul add def
/yP yStart pasX \iA\space sin mul add def
}]{\FieldLines
/xP xP dX add def /yP yP dY add def xP yP }%
}
\pscustom{
\code{
0 1 NoQ { /i exch def
i getX i getY \ScreenCoor\space 10 i getQ abs mul 0 360 arc
gsave i getQ 0 gt {1 0 0}{0 0 1}ifelse setrgbcolor fill grestore
stroke
} for
}}
}
%
\multido{\rX=-8.1+0.5}{32}{%
\psparametricplot[plotpoints=1000,linecolor=blue]{0}{1}[{
/xStart 0 getX  def
/yStart 0 getY def
/pasX 0.017 def
/xP \rX\space def
/yP 0 def
}]{\FieldLines
/dY Ex NormeE div pasX mul neg def
/dX Ey NormeE div pasX mul def