Calculation of Magnetic Fields due to Line Currents

A modified form of the Biot-Savart law is derived which is of particular use in the calculation and/or graphical determination of the magnetic fields due to line currents. In a linear conductor carrying a uniform current, I, the magnetic intensity at an observation point is given by \begin{equation*}H = \frac{2I}{R}{sin}\left(\frac{\alpha}{2}\right)\end{equation*} where α is the viewing angle to the conductor extremities and R is the effective distance measured from the observation point to the conductor along the viewing angle bisector. Examples of the application of this formula are given. These illustrate the usefulness of the formula in simplifying EMC analyses involving circuit and system emanations.