Halliday, Resnick & Walker — Magnetic Fields: Problem 14

14 Figure 28-27 shows a wire ring of radius \( a = 1.8 \text{ cm} \) that is perpendicular to the general direction of a radially symmetric, diverging magnetic field. The magnetic field at the ring is everywhere of the same magnitude \( B = 3.4 \text{ mT} \), and its direction at the ring everywhere makes an angle \( \theta = 15^\circ \) with a normal to the plane of the ring. The twisted lead wires have no effect on the problem. Find the magnitude of the force the field exerts on the ring if the ring carries a current \( i = 4.6 \text{ mA} \).