A law of the form
where dB is the infinitesimal element of the magnitude of the magnetic flux density (see magnetic field) at a distance r at a point P from the element length dl of a conductor, μo is the magnetic permeability of free space, I is the current flowing through the conductor, and θ is the angle between the direction of the current and the line joining the element of the conductor and P. It is also called the Ampère–Laplace law after the French mathematician Pierre-Simon de Laplace (1749–1827). There are several mathematically equivalent statements of this law.