magnetfelt

Magnetfelt, or magnetic field, is a vector field that describes the magnetic influence of electric charges in motion and of magnetic materials. It exists in space around current-carrying conductors and around permanent magnets, and it can exert forces on moving charges and on magnetic dipoles. The direction and strength of the field at a point are indicated by the field vector B at that location.

Two related quantities are used to describe the field: B, the magnetic flux density, and H, the magnetic field strength. In vacuum, B = μ0 H, where μ0 is the permeability of free space. The unit of B is the tesla (T). In materials, B and H are linked by the material’s magnetization M and permeability μ = μ0 μr. Maxwell's equations govern how magnetic fields are generated and altered: ∇·B = 0 and ∇×H = J + ∂D/∂t, with changing electric fields also producing B through Faraday’s law, ∇×E = -∂B/∂t.

Sources include permanent magnets, which produce a static field from aligned electron spins, and electric currents, which create fields described by the Biot–Savart law or Ampère's law. Time-varying currents and changing electric fields produce dynamic magnetic fields. The Earth’s geodynamo generates a large-scale magnetic field that shields the planet from charged particles. Common examples of magnetic fields are the dipole field around a bar magnet and the uniform field inside an electromagnet.

Applications of magnetfelt are widespread and include electric machines (motors, generators), transformers, magnetic resonance imaging, particle accelerators, and magnetic sensing. Measurement and sensing are performed with magnetometers and Hall-effect sensors, while protective shielding and magnetic materials are used to manage stray fields. The concept is central to both fundamental physics and engineering.