Biot-Savart Law

The integral law that gives the magnetic flux density B(r) produced by a steady current distribution J or a filamentary current I: for a current element in vacuum, dB(r) = (μ0/4π) · (I dl × r̂)/r^2 and B(r) = (μ0/4π) ∫ (I dl' × (r−r'))/|r−r'|^3, integrated over the current path or volume.