magnetic field

Region around a permanent magnet, or around a conductor carrying an electric current, in which a force acts on a moving charge or on a magnet placed in the field. The field can be represented by lines of force parallel at each point to the direction of a small compass needle placed on them at that point. These invisible lines of force are called the magnetic field lines or flux lines. A magnetic field's magnitude is given by the magnetic flux density (the number of flux lines per unit area), expressed in teslas. See also polar reversal. Experiments have confirmed that homing pigeons and some other animals rely on their perception of the Earth's magnetic field, together with other cues, for their sense of direction.