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   \begin{tikzpicture}
   \pgfmathsetlengthmacro{\scale}{1cm};
   %
   %Layout anchors:
   \node(e) at (0,0){electrons};
   \node[below left=\scale of e](l){};
   \node[below right=\scale of e](r){};
   \pgfmathparse{\scale * 4};
   \node[below = \pgfmathresult pt of e](screen){};
   %
   %B-field:
   \node[draw,fill=gray, minimum width = \scale*1.2, minimum
   height=\scale*1.2, below =\scale*0.9 of e]{};
   \node[draw,fill=white, minimum width = \scale, minimum height=\scale, below =
   \scale of e](B){$B$};
   \pgfmathparse{\scale * 0.4};
   \draw[->,blue] ($(B.east)+(-0.1*\scale,0)$) arc(0:340:\pgfmathresult pt);
   %
   %Double Slid
   \pgfmathsetlengthmacro{\width}{\scale * 3};
   \pgfmathsetlengthmacro{\thick}{\scale * 0.1};
   \draw[black,fill=gray] (l.west) rectangle +(-\width,\thick);
   \draw[black,fill=gray] (r.east) rectangle +(\width,\thick);
   \draw[black,fill=gray] ($(l.east)+(0.1*\scale,0)$) rectangle
   ($(r.west) + (-0.1*\scale,\thick)$);
   %
   %Screen
   \draw[black,fill=gray] ($(screen)+(2*\width,0)$) rectangle +(-4*\width,-\thick);
   \node[right=3*\scale of screen, yshift=\thick]{screen};
   \node[yshift=3*\thick, left= \thick of screen] {interference} ;
   %
   %beams:
   \path[->, red] (e) edge[bend right] node[black,left=0.2cm, near start]{path one} (l)
   edge[bend left] node[right=0.2cm, near start,black]{path two} (r)
   (l) edge (screen)
   (r) edge (screen);
   %
   \end{tikzpicture}