Hi, My understanding of an electromagnet is that it is a material with low susceptibility and high permeability, i.e. the magnetic field is not permanent but in the application of a current then the material gets a large magnetic field. In the application of a current the spins of the electrons in the material align in the same direction so the material gets a net "magnetic moment" or magnetic field. I have read on Wikipedia that the magnetic core "focuses" the field caused by the current so the field strength increases by thousands of times. I also know that the current is caused by an electric field drawing the loose valance electrons forward to make a flow of electricity. So my question is this: if you had a hypothetical wire that had in its interior a vacuum, and a shell that no electrons could escape from, could this wire, if wrapped around a material with high permeability, generate a magnetic field? I am not sure if the electrons have to escape the wire and go into the magnetic core for the material to get a magnetic field.