The magnetic flux density (magnetic field, magnetic induction, B field, or B) is a vector field describing magnetic forces throughout a volume. Its relationship to an electric field (E) is defined by Maxwell's equations and is illustrated by the Lorentz force law:
F = q(E + v × B)
The unit is the tesla (SI) or gauss (CGS).
Another measure of magnetism is the magnetic field strength (H). The physical quantities (B and H) are equivalent for the portion of a magnetic field in a vacuum, but differ where the magnetic field is passing through some material.