This law is an alternative to the Biot-Savart law for deriving the expressions for the magnetic flux
density of a field. It states that the line integral of the flux density around a closed path is equal
to the product of the current enclosed by the path and the permeability of the material, that is:
∫ B cos dL = oI
where is the angle between a short length of path dL and the direction of the field at that point.
For example the line integral for a straight wire is 2r, and so the equation becomes:
B2r = oI therefore B = oI/2r