Trying to determine the strength of an electromagnet in Teslas, with an iron core. Some sites have the same basic formula but with different units after B= Some use μ0, μr, or μ. Which one to use? For N (the number of turns), is this the general number of turns accounting for multiple layers, or turns per meter (or inches), or what? And L (the length), is it the length of the iron core or the length of the wire used, and should it be in meters or inches? According to this site (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html), a 0.1 meter (4") length solenoid (I'm assuming their talking about the iron core?) with 200 turns, 1 amp, and an iron core with 200 relative permeability is 0.5 Tesla. With 3 amps, this is about 1.5 Tesla and that doesn't sound right. Any help is appreciated, thanks!