# Magnetic field

A vector-valued function of space-time variables describing a force acting on a moving electrical charge and proportional to the charge velocity in the following sense. The total force $\overset{\rightharpoonup} { F }$ which acts on a charge $q$ moving with velocity $\overset{\rightharpoonup }{ v }$ is given by the Lorentz force law
where $\overset{\rightharpoonup }{ E }$ is the electric intensity field. The vector $\overset{\rightharpoonup} { B }$ is called the magnetic field (see, e.g., [a1], Sect. 1). However, quite often $\overset{\rightharpoonup} { B }$ is considered as a vector of magnetic induction (see, e.g., [a2], Sect. 29), while the vector $\overset{\rightharpoonup }{ H }$ related to $\overset{\rightharpoonup} { B }$ by the material equation $\overset{\rightharpoonup} { B } = \mu \overset{\rightharpoonup}{ H }$ is named magnetic intensity field or simply magnetic field. Here, $\mu$ denotes the material permeability. Together with the electric intensity field $\overset{\rightharpoonup }{ E }$, the vector $\overset{\rightharpoonup} { B }$ satisfies the Maxwell equations.