Overview
Magnetism is a physical phenomenon by which materials exert attractive or repulsive forces on other materials. It arises from the motion of electric charges and from the intrinsic magnetic moments of elementary particles. The region around a magnet or a moving charge where magnetic forces act is called a magnetic field. For a general introduction see magnetism and its role in physics.
Fundamental characteristics
Magnetic behavior is commonly described by field lines, magnetic flux, and intensity. The SI unit of magnetic flux density is the tesla. Materials respond differently to magnetic fields: ferromagnetic materials (notably iron, nickel and cobalt) can retain strong magnetization; paramagnetic substances are weakly attracted; diamagnetic materials are weakly repelled. These responses depend on atomic-level arrangements known as magnetic domains and on electron spin and orbital motion.
Types of magnets and magnetic materials
- Permanent magnets: made from ferromagnetic alloys that keep magnetization without an applied field.
- Electromagnets: coils of wire that produce magnetism when electric current flows.
- Soft magnetic materials: designed to magnetize and demagnetize easily for transformer cores and motors.
Further reading on commonly used materials and classification is available at magnetic materials.
History and scientific development
Interest in magnetism goes back to ancient observations of naturally magnetized stones. Scientific understanding advanced when researchers discovered links between electricity and magnetism; experiments showed that electric currents create magnetic fields, which led to the unified theory of electromagnetism and the development of practical devices. Key ideas from classical electromagnetism explain how changing electric fields and currents produce magnetic effects.
Applications and importance
Magnetism underpins many technologies: electric motors and generators convert between magnetic and mechanical energy; magnetic storage media record information; magnetic resonance imaging (MRI) uses strong, controlled fields for medical imaging; compasses and geomagnetic studies rely on Earth's magnetic field. Electromagnetic devices are central to power generation, transportation, and communications.
Distinctions and notable facts
Magnetism is closely related to, but distinct from, static electric forces; moving charges and changing electric fields are essential for magnetic phenomena. While everyday magnets attract iron, many materials show subtler magnetic properties only detectable with sensitive instruments. For authoritative summaries and technical introductions consult standard physics references and educational resources via physics portals or specialist pages such as magnetism overview and material guides.