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Why do charged particles move in circles in a uniform magnetic field?

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Learn about magnetic fields and the levels of particles, atoms, crystals, and domains — magnet Magnetic fields and the levels of magnetism of particles, atoms, crystals, and domains.

When a charged particle moves through a uniform magnetic field, it experiences a force known as the Lorentz force. This force is exerted only when the particle is in motion and acts in a direction perpendicular to both the particle's velocity and the magnetic field lines.123

Because the magnetic force is always directed at a right angle to the particle's velocity, it does not change the particle's speed, but it does continuously change its direction of motion. When the particle's velocity is perpendicular to the magnetic field, this constant, perpendicular force acts as a centripetal force, causing the particle to follow a circular trajectory. The radius of this circular path is determined by the particle's mass, velocity, charge, and the strength of the magnetic field.1453

If the particle has a velocity component parallel to the magnetic field, it will trace out a helical path instead of a simple circle, as the parallel component of its motion remains unaffected by the magnetic force.124