Then we measure the magnetic constant (μ 0 ) and use that value along with the speed of light to calculate the electric constant (ε 0 ). This is described by the Biot-Savart law:You can see the magnetic constant (μ 0 ) in there. So this says the magnetic field increases with the electric charge and decreases with the distance (r) from the moving charge—and the magnetic constant tells us precisely how much it varies. It’s EverywhereWhat this tells us is that electric current generates a magnetic field. Just as a changing electric field creates a magnetic field, a changing magnetic field creates an electric field—and that produces an electric current.