A vector field showing how magnetic forces are distributed in space. A magnetic field describes how the magnetic force at a given point in space will act on a ferromagnetic object or charged particle. In a magnetic field, the Lorentz force on a charged particle is perpendicular to both the direction of the magnetic field and its velocity. Magnetic fields surround magnetized objects, are formed around conductors through which electric current flows, or at a point with a varying electric field. It is described by the quantities B and H. B is the magnetic flux density and is given in units of tesla. A common refrigerator magnet is usually 0.001 tesla. The quantity H describes the magnetic field strength and is expressed in amperes per meter.
Rotating magnetic fields are used by electrical generators in power plants.
In thermonuclear fusion research, a strong magnetic field is used to confine hot plasma in tokamaks and stellarators.