In the amperian loop model, which applies for macroscopic currents, the gyromagnetic ratio is one half of the charge-to-mass ratio. This can be shown as follows. The angular momentum of a moving charged particle is defined as: L = r × × p = μ μ r × × v , where μ is the mass of the particle and v is the particle's velocity. The angular momentum of the very large number of charged particles that make up a current therefore is: L = ∭ ∭ V r × × ( ρ ρ v ) d V , where ρ is the mass density of the moving particles. By convention the direction of the cross product is given by the right-hand rule.