Add illustration for Serway and Jewett v8's problem 24.21.

diff --git a/latex/problems/Serway_and_Jewett_8/problem24.21.tex b/latex/problems/Serway_and_Jewett_8/problem24.21.tex
index f7f765675608a52eab2f7106947edf90f4535029..b296b5f877be2c18a20272a4d26e29a3f1e6f53d 100644 (file)
--- a/latex/problems/Serway_and_Jewett_8/problem24.21.tex
+++ b/latex/problems/Serway_and_Jewett_8/problem24.21.tex
@@ -8,11 +8,29 @@ face $c$, \Part{d} face $d$, and \Part{e} the top and bottom faces of
 the cube.  \Part{f} What is the net electric flux through the
 cube?  \Part{g} How much charge is enclosed within the gaussian
 surface?
+\begin{center}
 %           ^
 %    a      E\th|
 %  d   b      \ |
 %    c         \|
-
+\begin{asy}
+import Mechanics;
+import ElectroMag;
+
+real u = 1cm;
+real theta = 90 + 25;
+
+vector_field(width=2.4u, height=2.4u, EField(dir=theta));
+draw(scale(2*u)*shift((-0.5,-0.5))*unitsquare, dashed);
+label("$a$", (0,u), align=N);
+label("$b$", (u,0), align=E);
+label("$c$", (0,-u), align=S);
+label("$d$", (-u,0), align=W);
+pair c = (u,-0.35u);
+Angle a = Angle(c+(0,1), c, c+dir(theta), fill=currentpen, L="$\theta$");
+a.draw();
+\end{asy}
+\end{center}
 \end{problem*}
 
 \begin{solution}