Magnetic force on a current and on charged particles

PhysicsElectric & Magnetic FieldsAges 17–18

Wire mode: a wire segment of length l carrying current I sits in a uniform magnetic field B at angle α; the magnetic force F = BIl·sinα is found with the left-hand rule — drag to rotate the wire and watch F change. Particle mode: a charged particle (proton or electron) enters the magnetic field perpendicularly; the Lorentz force f = |q|vB makes it move in a circle of radius r = mv/(|q|B) with period T = 2πm/(|q|B).