= Free current
A <free current> is the part of the macroscopic <electric current> assigned to mobile or externally supplied <electric charges>, rather than to the bound motion represented by <polarization> and <magnetization>. In a conductor, drifting conduction <electrons> provide a familiar example.
In macroscopic <Maxwell's equations>, the free-current density appears as $\nabla\times\mathbf H=\mathbf J_{\mathrm f}+\partial\mathbf D/\partial t$. Here $\mathbf H$ is the <magnetic field strength> and $\mathbf D$ the <electric displacement field>. The separation depends on the material model; the total microscopic charge motion remains the source of the electromagnetic field.
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