A wire with current $i=3.00 \mathrm{A}$ is shown in Fig. $29-53 .$ Two
semi-infinite straight sections, both tangent to the same circle, are connected
by a circular arc that has a central angle
$\theta$ and runs along the circumference of
the circle. The arc and the two straight
sections all lie in the same plane. If $B=$
0 at the circle's center, what is $\theta$ ?