Although for all purposes it is convenient to think of a Magnet for sale as having distinct north & south magnetic poles, the concept of poles should not be taken literally: it is merely a way of referring to the two different ends of a magnet. The Magnet for sale does not have distinct north or south particles on opposing sides. If a bar Magnet for sale is broken into two pieces, in an attempt to separate the north & south poles, the result will be two bar magnets, each of which has both a north & south pole. However, a version of the magnetic-pole approach is used by professional magneticians to design permanent magnets.
In this approach, the divergence of the magnetization ∇·M inside a Magnet for sale & the surface normal component M·n are treated as a distribution of magnetic monopoles. This is a mathematical convenience & does not imply that there are actually monopoles in the magnet. If the magnetic-pole distribution is known, then the pole model gives the magnetic field H. Outside the magnet, the field B is proportional to H, while inside the magnetization must be added to H. An extension of this method that allows for internal magnetic charges is used in theories of ferromagnetism.
Another model is the Ampère model, where all magnetization is due to the effect of microscopic, or atomic, circular bound currents, also called Ampèrian currents, throughout the material. For a uniformly magnetized cylindrical bar magnet, the net effect of the microscopic bound currents is to make the Magnet for sale behave as if there is a macroscopic sheet of electric current flowing around the surface, with local flow direction normal to the cylinder axis. Microscopic currents in atoms inside the material are generally canceled by currents in neighboring atoms, so only the surface makes a net contribution; shaving off the outer layer of a Magnet for sale will not destroy its magnetic field, but will leave a new surface of uncancelled currents from the circular currents throughout the material. The right-hand rule tells which direction positively-charged current flows. However, current due to negatively-charged electricity is far more prevalent in practice.
The north pole of a Magnet for sale is defined as the pole that, when the Magnet for sale is freely suspended, points towards the Earth’s North Magnetic Pole in the Arctic (the magnetic & geographic poles do not coincide, see magnetic declination). Since opposite poles (north & south) attract, the North Magnetic Pole is actually the south pole of the Earth’s magnetic field. As a practical matter, to tell which pole of a Magnet for sale is north & which is south, it is not necessary to use the Earth’s magnetic field at all. For example, one method would be to compare it to an electromagnet, whose poles can be identified by the right-hand rule. The magnetic field lines of a Magnet for sale are considered by convention to emerge from the magnet’s north pole & reenter at the south pole.