Final answer:
When a proton moves perpendicular to a magnetic field, it follows a circular path due to the force exerted on it. The magnitude and direction of this force can be determined using the right-hand rule and the equation F = qvB.
Step-by-step explanation:
When a proton moves perpendicular to a magnetic field, it follows a circular path. This is because the magnetic field exerts a force on the proton, causing it to experience centripetal acceleration towards the center of the circular path. The magnitude of the force can be determined using the equation F = qvB, where F is the force, q is the charge of the proton, v is its velocity, and B is the magnetic field strength. The direction of the force is given by the right-hand rule, which states that if you point your thumb in the direction of the velocity and your fingers in the direction of the magnetic field, the force will be perpendicular to both.