[Image of iron filings forming a pattern around a magnetic field.]
The iron filings show us the pattern of the magnetic field outside the magnet. The poles of the magnets have more iron filings than the center of the magnet. We created a rule according to which the magnetic field lines leave the north pole and go towards the south pole.
Magnetic fields travel through everything, so they also travel through the material that makes up the magnet. Thus, each field line forms a loop.
We say that the magnetic field indicates the direction in which the north pole of a compass would point if it were placed at that point. The movement of the smoke indicates the direction in which an invisible wind is moving. The north pole of a compass is the best way to see which way a magnetic field is pointing.
Einstein said that the extra electron spins in certain atoms create an imbalance that makes the atom act like a little magnet. Iron atoms form domains where, in a local region, all atomic spins align.
The black arrows represent the north poles of the iron atoms. In this domain the atoms all point in the same direction. When an external magnetic field (the red arrows) is imposed on the iron atoms, they all line up with the magnetic field.
The Earth has a magnetic field inside it. Somehow, the swirling molten iron, as the Earth spins on its axis, close to its solid core, creates a large magnetic field that, surprisingly, acts like a bar magnet at the center of the Earth.
The drawing below shows only the top half of a magnetic field around a bar magnet.
The dark triangle represents the north pole of a compass pointing to the south pole of the magnet. The field lines then travel through the bar magnet and emerge at the north pole of the magnet, where they are repelled and thus rotate back to the south pole again.
Hang a magnet where it is freely suspended.
The north pole is the north-seeking pole, which points toward the northern hemisphere, where it is attracted by the Earth’s south magnetic pole, because only opposite poles can attract.