Исходники иллюстрации

\documentclass[tikz]{standalone}\input{pre.tex}\begin{document}\begin{tikzpicture}
    \contourlength{0.5mm};

    \draw[very thick] (0,-1.5) -- (0,1.5);
    \draw[magenta] (0,0) node[] {\contour{white}{$\bigodot$}} node[right, xshift=.5em] {$O$};

    \draw[magenta] (0,1) node[] {\contour{white}{$\times$}};

    % \draw[interface] (-2,0) rectangle (2,-0.25);
    % \draw[thick] (-2,0) -- (2,0);

    % \draw (0,1) circle (1);



 %    \draw[fill=magenta] (0,0) circle (2pt) node[above, yshift=3pt] {\contour{white}{$B$}};
    \lineann[1.5]{90}{1}{$x$}
    \begin{scope}[yshift=-1.5cm]        
    \lineann[1]{90}{3}{$l$}
    \end{scope}

    \draw[fill=magenta] (2,1) circle (2pt);
    \draw[->] (2,1) -- ++ (-0.5,0) node[left] {$\vec{v}$};

    \draw (-2.5,0) node[blue] {$\bigotimes$} node[right, xshift=.5em] {$\vec{g}$};

\end{tikzpicture}\end{document}