$\bullet$ A beam of protons traveling at 1.20 $\mathrm{km} / \mathrm{s}$ enters a uniform magnetic field, traveling perpendicular to the field. The beam exits the magnetic field in a direction perpendicular to its original direction (Fig. $20.60 ) .$ The beam travels a distance of 1.18 cm while in the field. What is the magnitude of the magnetic field?