\documentclass[tikz]{standalone}
\usepackage{tikz}

\usetikzlibrary{calc}
\usetikzlibrary{intersections}
\usetikzlibrary {backgrounds}
\begin{tikzpicture}[scale=3, background rectangle/.style={fill=gray!20}, show background rectangle]
  \draw[ultra thick] (0, 0.05) -- (0, 1);
  \draw[ultra thick] (0, -.05) -- (0,-1);
  \node[above left] at (0, 0) {$S$};
  \draw[ultra thick] (1, 0.55) -- (1, 1.5);
  \draw[ultra thick] (1, -.55) -- (1,-1.5);
  \draw[ultra thick] (1, -.45) -- (1, .45);
  \node[above left] (S1) at (1, .5) {$S_1$};
  \node[below left] (S2) at (1,-.5) {$S_2$};
  \node[above left] at (1,  0) {$o^{\prime}$};
  \draw[thick] (5,-1.7) -- (5, 1.7) -- (5.1, 1.7) -- (5.1,-1.7);
  \node[below right, purple] at (5.1, 1.7) {$p$};
  \node[below right] at (5.1, 0) {$o$};
  \draw[magenta, dashed, <->] (1, -1.4) -- (5, -1.4);
  \node[magenta, below] at (3, -1.4) {$d^{\prime}$};
  \draw[dotted, thick] (-.4, 0) -- (5.5, 0);
  \draw[dotted, thick] (.2, .5) -- (1, 0.5);
  \draw[dotted, thick] (.2,-.5) -- (1,-0.5);
  \draw[magenta, dashed, <->] (0.5, 0.5) -- (0.5, -.5);
  \node[magenta, right] at (0.5, 0) {$d$};
  \draw[orange] (0, 0) -- (1, 0.5) -- (5, 1.25);
  \node[orange] at (3.5, 1.2) {$r_1$};
  \draw[orange] (0, 0) -- (1, -.5) -- (5, 1.25);
  \node[orange] at (3.8, 0.5) {$r_2$};
  \node[above left] (B) at (5, 1.25) {$B$};
  \draw[blue, dashed, thick] (1,0) -- (5, 1.25);
  \draw[green, thick] (2, 0) arc [radius=0.27, start angle=-20, end angle=50];
  \node[green, above left] at (2, .05) {$\theta$};
  \draw[dotted, thick] (5.1, 1.25) -- (5.4, 1.25);
  \draw[magenta, dashed, <->] (5.3, 0) -- (5.3, 1.25);
  \node[magenta, right] at (5.3, .7) {$x$};
  \node (E) at ($(1,-.5)!(1,.5)!(5,1.25)$) {};
  \draw[name path=line1, dashed, thick] (1, .5) -- (E) -- +($(E)-(1,.5)$);
  \draw[dashed, thick] (1,-.5) -- +($(E)-(1,.5)$);
  \draw[green, thick] (1,-.3) arc [radius=0.3, start angle=-100, end angle = -35];
  \node[green, above right] at (1.05,-.25) {$\theta$};
  \node (H) at ($(1,-.5) + 0.5*(E) - 0.5*(1,.5)$) {};
  \path[name path=line2] (H) -- +($(5,1.25)-(1,-.5)$);
  \path[name intersections={of=line1 and line2}];
  \draw[magenta, dashed, <->] (H) -- (intersection-1);
  \node[magenta, above right] at (1.3, -1) {$\Delta r$};
  \node[above right] at (0,-1.5) {$d\ll d^{\prime}$};
\end{tikzpicture}