Just as static charges produce an electric field, the
currents or moving charges produce (in addition) a
magnetic field, denoted by B (r), again a vector field It
has several basic properties identical to the electric field It is defined at each point in space (and can in addition
depend on time) Experimentally, it is found to obey the
principle of superposition: the magnetic field of several
sources is the vector addition of magnetic field of each
individual source