My physics textbook defines the direction of the magnetic field as the direction of the force on a small north pole of a magnet. However, I am told also that if you have, say a bar magnet, that the north pole has a field coming out of it and curving towards the south pole. But we are also told that it then continues back and returns to the north pole, why? It doesn't make sense, does it, that a small north pole of a tiny magnet would go back from the south pole to the north pole, which it is repelled from!
Here's an icon of that sort from the internet.
Image from http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html
See the curve of the electromagnetic field, why does it come to the southern pole and then heads back to the north pole? What causes a tiny north pole to want to go back north?
Best Answer
First, there is no such thing in real life as an isolated North or South pole. This implies that magnetic field lines always form closed loops, as you see in the image. This is codified in Gauss's Law of Magnetism.
Your textbook, while I can sort of see the logic, gives a very inelegant definition for field lines. Don't think of the field lines as a force on a tiny test bar magnet that will push it. Think of it as forcing the tiny magnet to orient a certain way. If you had a compass (which is precisely a tiny magnet), and put yourself as a tiny person into your diagram and started walking around, your compass would always point in the direction of the local field line, including if you were inside the bar magnet. Hope that is helpful