You need to use a material featuring an high magnetization under the same H magnetic field (which depends on the current flowing through and the geometry of the coil only). This property is called ferromagnetism and it is typical of a few elements (iron, cobalt nichel and gadolinium around room temperature) and their alloys. Magnetization is a phenomenon caused by the alignment of internal magnetic field due to electronic spin with an the external magnetic field
-Why must you use an iron core to make an electro magnet? Why can you use things like plastic or aluminum?
Otherwise the magnetic fields produced by each coil would cancel each other-Why must you wind the wire in the same direction around the iron core to make make the electromagnet.
the magnetic fields would partially cancel each other-What happened if some of the wire is wound in one direction and some of the wire is wound in the other direction?
using a ferromagnetic core of high susceptivity and creating a stronger H field by either increasing the current in the coil or the number of coils per unit of lenght-How could you make an electromagnet stronger?