1. The problem statement, all variables and given/known data I have a magnetic circuit with a coil wrapped around the centre "leg" of the core as follows. I have been given average lengths, areas and permeabilities for the three legs and the airgap. 2. Relevant equations L = (N^2*µ*A)/l 3. The attempt at a solution For the core material permeability(µ) do I specifically use the permeability of the part of the core the coil is wrapped around? (As mentioned, in this example I was given different permeability for the different "legs") Similarly for the coil area(A) and average coil length(l), if these are not specified separately, do I use the dimensions of the centre leg?