An alpha particle (consisting of two protons and two neutrons) is moving at constant speed in a circle, perpendicular to a uniform magnetic field applied by some current-carrying coils, making one...

An alpha particle (consisting of two protons and two neutrons) is moving at constant speed in a circle, perpendicular to a uniform magnetic field applied by some current-carrying coils, making one clockwise revolution every 80 nanoseconds (Figure 21.81). If the speed is small compared to the speed of light, what is the numerical magnitude B of the magnetic field made by the coils? What is the direction of this magnetic field?