Walker, Halliday & Resnick — Magnetic Fields Due to Currents: Problem 59

59 A wire with current \( i = 9.50 \text{ A} \) is shown in Fig. 29-63. 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 the magnetic field is \( B = 0 \) at the circle’s center, what is \( \theta \)?