1. The problem statement, all variables and given/known data The attached picture shows a spool coil on a iron core with an air gap measuring 2.5mm. The spool is coiled by 0.5mm2 with rho cu = 0.0175 Ωmm2 /m. The average winding diameter for the spool is 3.18cm. Compute the magnetic flux in the spool. 2. Relevant equations 3. The attempt at a solution Using the equation: phi = I * N / Rm, I still miss I, and I have no idea how to compute it. Rm is the reluctance which I can get from a B-H characteristic - if that applies to this problem. My first questions are these I guess: Is this the correct formula? If yes, how to I compute I? Any feedback and help is as always greatly appreciated. Thanks.