In a typical application the term "flux linkage" is used when the flux is created by the electric current flowing through the coil itself. Per Hopkinson's law, Ψ Ψ = n M M F R , where MMF is the magnetomotive force and R is the total reluctance of the coil. Since M M F = n I , where I is the current, the equation can be rewritten as Ψ Ψ = L I , where L = n 2 R is called the inductance. Since the electrical reactance of an inductor X = ω ω L = 2 π π f L , where f is the AC frequency, X = ω ω Ψ Ψ I .