%&tex
\documentclass{standalone}
\usepackage{tikz}
\usepackage{siltex}
\usetikzlibrary {calc,arrows.meta,positioning,patterns}
\input{graphics/tics.tikz}

\begin{document}
\begin{tikzpicture}[thick, on grid, x = 1.16cm, y = 1.16cm, >=Stealth]
    \clip[draw=none] (-0.7,-0.9) rectangle (2.12,2.2);
    \draw(-2,-2.75) pic {whiteboard};
    \filldraw[pattern = north west lines, pattern color=gray!60,draw=gray!60] (-2.1,0) -- (2.1,0) arc[start angle = 0, end angle = 180, radius=2.1] -- cycle;
    \draw[fill=gray] (0,0) circle (0.2);
    \begin{scope}[rotate=60,shift={(0.5,0)}]
            \draw[fill=gray!60] (-1,0.05) rectangle (1.5,-0.05);
            \draw[<->] (0.2,0.15) -- node[midway,above left]{$r$} (0.8,0.15);
            \begin{scope}[shift={(-0.3,0)}]
               \draw[<->] ({0.8*cos(160)},{0.8*sin(160)}) arc[start angle = 160, end angle= 200, radius = 0.8] node[midway, below left]{$\Phi$};
            \end{scope}
    \end{scope}
\end{tikzpicture}
\end{document}