By Jo Pick | Updated Mar 24, 2022
Atoms possess microscopic north and south poles—just like Earth’s magnetic field. In most materials, these poles point in random directions, so the material remains non‑magnetic. When the atomic poles align, as can be achieved with an electric current, the substance exhibits a net magnetic field.
The quintessential example is the crane‑mounted electromagnet that lifts cars and scrap metal by the ton. Switching the current on turns the iron core into a magnet; turning it off demagnetizes it. Smaller everyday applications include doorbell magnets, which pull a striker to ring the bell, and the electromagnetic speaker cones that reproduce sound by vibrating in response to an audio‑driven current.
Electric motors convert alternating magnetic fields into rotational motion. A varying current produces fluctuating magnetic fields that exert torque on the motor’s rotor. Motors are integral to virtually every mechanical system—from car engines and household appliances to computer hard‑disk drives and automatic retail doors.
Magnetic media record data by magnetizing tiny regions of a surface. A read/write head—essentially a miniature electromagnet—creates a magnetic pulse that writes a bit; when the head passes over the same spot, the induced field generates a voltage that the computer interprets as data. Because the head does not physically touch the medium, reading and writing occur at very high speeds.
Maglev trains harness magnetic repulsion to hover above the rails, eliminating mechanical friction. This principle, derived from the same physics that underlies hard‑disk drives, allows trains such as Japan’s Shinkansen to reach remarkable speeds while maintaining precise, single‑track routing.
From industrial cranes to high‑speed rail, magnetic fields are the invisible force that drives many of today’s technological advancements.
