1. The problem statement, all variables and given/known data A cast steel magnet has an air gap of length 1mm and an iron path of 30cm. Find the magneto motive force (MMF) necessary to produce a flux density of 1Wb/m^2. The relative permeability of cast steel is 900. Neglect any leakage or fringing effects 2. Relevant equations I think these are relevant Flux density B = mu H Magnetic field strength H = (NI)/L Permeance Mu = Mu0 MuR where Mu0 = 4pi *10^-7 and MuR is the relative permeability MMF = NI 3. The attempt at a solution i first equated flux density and magnetic field strength together to make B = 1 = Mu * (NI)/L i worked Mu out to be approx 1.131*10^-3 Then substituted L as 0.3metres. this then worked out to be NI = 0.3 * (1.131*10^-3) NI is then 3.39*10^-4. Which is the MMF. Is this correct? Do i have to use the air gap of 1mm for anything? Your help is appreciated.