A magnetic field is a vector field that describes the magnetic influence on
moving electric charges, electric currents, and magnetic materials. A moving
charge in a magnetic field experiences a force perpendicular to its own velocity
and to the magnetic field. A permanent magnet′s magnetic field pulls on
ferromagnetic materials such as iron, and attracts or repels other magnets.
In addition, a magnetic field that varies with location will exert a force on
a range of non-magnetic materials by affecting the motion of their outer atomic
electrons. Magnetic fields surround magnetized materials, and are created by
electric currents such as those used in electromagnets, and by electric fields
varying in time. Since both strength and direction of a magnetic field may vary
with location, they are described as a map assigning a vector to each point of
space or, more precisely—because of the way the magnetic field transforms
under mirror reflection—as a field of pseudovectors.