sähkömagnetsisessa

Electromagnetism is the branch of physics that studies the interactions between electric charges and magnetic fields. The phenomena are described mathematically by Maxwell’s equations, four partial differential equations that relate electric and magnetic fields to their sources—electric charges and electric currents—and to each other. In the static limit, Coulomb’s law gives the electric field of a point charge and Ampère’s law gives the magnetic field produced by a steady current. The dynamic equations, Faraday’s law of induction and the Maxwell–Ampère law, show that a time-varying magnetic field induces an electric field and that electric currents generate magnetic fields.

The combination of electric and magnetic effects underlies a wide range of practical technologies. Electromagnets, which rely on electric currents to produce strong magnetic fields, are used in electric motors, generators, transformers and magnetic resonance imaging. The propagation of electromagnetic waves, solutions of Maxwell’s equations in vacuum, includes visible light, radio waves, X‑rays and other forms of radiation governed by the speed of light.

The theoretical framework of electromagnetism has been extended by special relativity, where electric and magnetic fields transform into each other under Lorentz transformations, unifying them into a single electromagnetic field tensor. Quantum electrodynamics further refines the theory, describing interactions as exchanges of photons—the quanta of the electromagnetic field. Despite its completeness, electromagnetism remains a living field of research, with ongoing studies exploring novel materials, metamaterials and quantum technologies that hinge on electromagnetic principles.