= Particle current
{title2=$J_N=-dN_L/dt$}
The rate at which particles cross an oriented surface, measured as particle count per unit time. If a local <continuity equation> has number density $n$ and current density $\mathbf j_N$, then $\partial_t n+\nabla\cdot\mathbf j_N=0$ and $J_N=\int_S\mathbf j_N\cdot d\mathbf S$. In a closed two-reservoir system, a left-to-right <particle current> is $-dN_L/dt=dN_R/dt$. Neutral particles carry this current without an associated <electric current>.
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