\documentclass{article}% Uwe Ziegenhagen/Herbert Voss
\usepackage[dvipsnames]{pstricks}
\usepackage{pst-plot,pst-node}
\parindent=0pt
\pagestyle{empty}
\begin{document}

\psset{unit=0.75}
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\psline[linewidth=2pt,linecolor=black!30](6,0.5)(6,14)
\psline[linewidth=2pt,linecolor=black!30](1,8.5)(6,7)
\psline[linewidth=2pt,linecolor=black!30](1.5,5.5)(11,8.5)
\rput(17,3){\huge $x$}
\rput(5.5,13){\huge $y$}
\rput(10.5,8.75){\huge $z$}
\rput(11,7.1){\huge $\vec{r}$}
%
\psline[linewidth=3pt]{<->}(6,7)(6,11.25)
\rput(5.35,9.4){\huge $R$}
\psline[linewidth=6pt,linecolor=Green]{->}(6.5,12)(4.75,12)
\rput(7.5,12.8){\huge $I d\vec{l}$}
%
\psellipse[doubleline=true,doublecolor=yellow,doublesep=5pt,linecolor=blue](6,7)(3,4.5)
\psline[linewidth=2pt](6,7)(17.5,3.5)
\psline[linewidth=5pt]{->}(6,11.38)(11.95,5.225)
%
\psarc[linewidth=6pt,linecolor=gray](6,8){3.4}{85}{95}
%
\psline[linewidth=5pt,linecolor=gray]{->}(12,5.15)(12,8.15)
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\psline[linewidth=5pt,linecolor=gray]{->}(12,5.15)(15,4.25)
%
\psline[linewidth=2pt](12,8.15)(15,7.25)(15,4.25)
%
\Cnode*[radius=0.2cm](12,5.15){a}
\rput(11.5,4.5){\huge $P$}
%
\rput(12.5,8.9){\huge $dB_y$}
\rput(14.5,3.4){\huge $dB_x$}
\rput(15.5,8){\huge $d \boldmath{\vec{B}}$}
%
\psarc[linewidth=1pt]{<->}(12,5){5.5}{133}{161}
\rput(7.2,8.5){\huge $\theta$}
\end{pspicture}

\end{document}