How to remember which way the magnetic field goes? For the case of a current in a wire, we learn the direction of the associated magnetic field by learning the right hand rule. But what about a bar magnet and the names 'north' and 'south' for the ends of the magnet? How can we remember which way the field goes then?
(This question is not 'which way does it go?' which I can look up. The question is 'how to remember that'? Or how best to learn it?)
 A: The names "north pole" and "south pole" for the ends of a magnet were introduced a long time ago, well before anyone understood how magnetism arises and how it relates to electric currents. When we learn physics and learn more about magnetism, it turns out that these are not very good names. But they have stuck so I am not about to get rid of them. However, I think there are two teaching methods, and one is better than the other.

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*First teaching method: introduce the words "north pole", "south pole" and explain that magnetic field lines go from north to south outside a magnet, and from south to north inside a magnet.


*Second teaching method: explain that magnetic field lines always run in loops, and there is a sense of direction around the loop. Draw a big loop and write the letters S and N next to it, like this:

The letters are written such that the direction of the field around the
loop is from S to N by the short route (and therefore from N to S by the long route). Then explain that these letters stand for "south" and "north" and are used for historical reasons (which I will explain in a moment).
To remember the direction one can turn the N into the tip of an arrow, with the S at the tail, like this:

Notice that in the second teaching method we have not yet introduced a bar magnet.
Next introduce a bar magnet and explain that the ends of such a magnet are commonly labelled "north" and "south" so as to show the direction of the loops of field produced by the magnet, as already explained above. The field around a bar magnet looks something like this:

If you really want to understand physics (as opposed to just learning rules), then teaching method 2 is better. Teaching method 2 makes it clear from the outset that the field lines run in loops and the purpose of the labels is to indicate a direction around a loop, not a place where something is happening. (This is different from electric charge, where a positive charge is a place where electric field lines point out, and a negative charge is a place where electric field lines point in.)
The next thing is to explain that north poles are attracted to south poles and repelled from north poles. So this leads to an amusing observation. The name "north pole", for a magnet, is assigned to the end of a magnet which points towards the Earth's north pole when the magnet is used as a compass. But this means the geographic north pole is a magnetic south pole! Oh dear!
It may interest the reader to know that in professional physics we mostly do not bother with the names "north pole" and "south pole". We focus on the magnetic field and which way it is running. We memorize how it relates to electric currents, and when dealing with dipoles (bar magnets are a bit like dipoles) we use an arrow to show the direction of the dipole, or in mathematical notion a vector. So "north" and "south" very rarely come up. They seem to persist as names for people to learn at school and then forget, of no use to any profession later in life except the school teaching profession! And so it goes on (in loops).
If you need to know the names "north" and "south" for an exam, then memorize the picture above of the arrow with an N at the tip, and the field line running in a loop. For a bar magnet the arrow on this diagram is sitting inside the magnet.
