Magnetic forces on moving charges and currents

A magnetic field exerts a force on an electric charge only when the charge moves across the field lines; a charge at rest, or one moving parallel to the field, feels no magnetic force. The force is strongest when the charge moves perpendicular to the field, and it points perpendicular to both the velocity and the field, a direction found with a right-hand rule. Because this force always acts sideways to the motion, it changes a charged particle's direction but not its speed, so a charge moving perpendicular to a uniform field travels in a circle. Mass spectrometers use this to sort ions by mass, and Earth's magnetic field steers charged particles from the Sun toward the poles, where they produce auroras. A current-carrying wire in a magnetic field feels a force too, since a current is moving charge: for a wire perpendicular to the field, the force equals field strength times current times the wire's length (F = B I L). A loop of current-carrying wire in a magnetic field feels a torque that turns it, and a simple DC electric motor keeps such a coil spinning by reversing the current in it every half turn.

This explanation is AI-generated and can occasionally be wrong. 🚩 Report