magnétiques

Magnétiques, in the sense of magnetism, refers to the phenomena associated with magnets and moving electric charges. The core concept is the magnetic field, a vector field that exerts forces on magnetic dipoles and on electric currents. Magnetic effects arise from the motion of charges and from intrinsic magnetic moments of elementary particles. The study spans fundamental physics and a wide range of technologies, and it is described by Maxwell's equations.

Materials respond to magnetic fields in distinct ways. Ferromagnetic substances such as iron, nickel, and cobalt can become strongly magnetized due to the alignment of microscopic magnetic domains and may retain magnetization as permanent magnets. Paramagnetic materials exhibit temporary alignment and weak attraction, while diamagnetic substances produce a weak, opposing response. In addition to permanent magnets, electromagnets use controlled electric currents to generate adjustable magnetic fields for practical use.

Historically, magnetism has roots in natural magnets and early experiments, with significant advances during the 19th century. Hans Christian Ørsted linked electricity and magnetism in 1820, followed by Faraday's law of induction and the developments of Ampère and Maxwell. Magnetic field strength is measured in tesla (T) in the SI system, while gauss remains a common non-SI unit in some contexts.

Applications of magnetism are widespread. They include electric machines such as motors, generators, and transformers; magnetic storage technologies; magnetic resonance imaging (MRI); sensors and actuators; and navigation with compasses. Magnetic materials and fields play a central role in electronics, telecommunications, transportation, and medicine, making magnétique phenomena foundational to modern technology.