File:MagFieldAngle.svg

\documentclass[crop,border=5,tikz,convert={outext=.svg,command=\unexpanded{pdf2svg
    \infile\space\outfile}},multi=false]{standalone}
\usetikzlibrary{math,calc,through,shapes,patterns,decorations.pathmorphing}

\newcommand{\markangle}[6][0.25]{
  \begin{scope}
    \clip (#2)--(#3)--(#4);
    \node (ANG) [draw, circle, minimum size=#5] at (#3){};
  \end{scope}
  \coordinate (E1) at (intersection 0 of ANG and #3--#2);
  \coordinate (E2) at (intersection 0 of ANG and #3--#4);
  \coordinate (EM) at ($ (E1)!0.5!(E2) $);
  \coordinate (EM) at ($ (EM)!#1!(#3) $);
  \node at (EM) {#6};
}

\begin{document}
\begin{tikzpicture}[>=latex,scale=1]
  \coordinate (A) at (210:1.4);
  \coordinate (B) at (30:1.4);
  \coordinate (O) at (0:0);
  \coordinate (C) at (-30:1.4);

  \foreach \x in {0.3,0.9,...,1.5}{
    \draw[thick,black!50!blue](\x,-1.5)--(\x,1.3);
    \draw[thick,->,black!50!blue](\x,-1.5)--(\x,0.1);
    \draw[thick,black!50!blue](-\x,-1.5)--(-\x,1.3);
    \draw[thick,->,black!50!blue](-\x,-1.5)--(-\x,0.1);
  }
  \node[black!50!blue] at (-1.2,1) {$\vec{B}$};

  \draw[ultra thick,black] (A)--(B);
  \draw[ultra thick,->,black] (A)--(30:0.8) node[below]{$I$};
  \draw[fill=white,ultra thick,draw=black!50!green] circle (2mm)
  node[below,black!50!green,inner sep=2.3mm] {$\vec{F}_{\mathrm{m}}$};
  \fill[black!50!green] circle (0.75mm);

  \draw[black,dotted] (A)-|(B);
  \draw[black] (A)--+(0,-0.4);
  \draw[black] (C)--+(0,-0.4);
  \draw[black] (A)--+(120:0.4);
  \draw[black] (B)--+(120:0.4);
  \draw[<->,black] ($(A)+(120:0.3)$)--($(B)+(120:0.3)$)
  node[midway,above]{$b$};
  \draw[<->,black] ($(A)+(0,-0.3)$)--($(C)+(0,-0.3)$)
  node[midway,below]{$b_{\mathrm{eff}}$};
  \markangle{C}{A}{B}{49}{\small $\varphi$}
\end{tikzpicture}
\end{document}