lelectromagnetisme

Lelectromagnetisme, or electromagnetism, is the branch of physics that studies the interactions between electric charges, currents, and the electric and magnetic fields they produce. Classical electromagnetism describes how stationary charges produce electric fields, how moving charges and currents produce magnetic fields, and how changing fields propagate and interact with matter.

These phenomena are unified by Maxwell's equations, a set of four partial differential equations that relate electric charge density and current to electric and magnetic fields. Gauss's law for electricity; Gauss's law for magnetism; Faraday's law of induction; and the Ampere-Maxwell law. Together they imply that time-varying electric and magnetic fields support the propagation of electromagnetic waves, including visible light, through vacuum or media.

Key implications include that light itself is an electromagnetic wave and that the speed of light in vacuum is a fundamental constant determined by the permittivity and permeability of free space. The theory also explains a wide range of phenomena from radio transmission to optical fibers, microwaves, and radar.

Historically, work by Coulomb, Ampere, Faraday, and others led to the formulation of Maxwell's equations in the 19th century; experimental demonstrations by Hertz confirmed electromagnetic waves. In the 20th century, quantum electrodynamics joined electromagnetism with quantum theory, describing interactions via photons.

Applications of electromagnetism are ubiquitous: electric power generation and distribution, motors and generators, transformers, wireless communication, sensors, imaging, and photonics. The field also intersects with relativity, since Maxwell's equations imply Lorentz invariance and the constancy of the speed of light.