= Current element
{title2=$I\,d\boldsymbol\ell'$}
A <current element> is the oriented infinitesimal wire contribution $I\,d\boldsymbol\ell'$ inside the <Biot-Savart law>. For uniform axial <current density> across <wire cross-sectional area> $A$, $I=JA$ and $d^3r'=A\,d\ell'$ imply $\mathbf J\,d^3r'=I\,d\boldsymbol\ell'$. This reduces a <volume integral> to a <line integral> in the thin-wire approximation. It is an integration contribution, not an isolated steady source. <Conventional current> runs opposite the drift of negatively charged <Electrons>.
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