Why does the earth’s magnetic field behave as it does, i.e. North / South,?
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Your question is a little vague, but I’ll do my best.
Magnetic fields are created by changes in an electric field (the reverse can also happen, but we aren’t focusing on that) so when you have current moving down a wire, a magnetic field is created around it as each electron moves through the wire. Materials can be magnetic because the electrons in each atom are moving, creating magnetic fields, but most of the time they cancel each other out. As to why each atom does a certain thing, it’s all very complicated quantum mechanics that isn’t fully understood, but we know which atoms are non magnetic, paramagnetic, and ferromagnetic.
The Earth’s outer core is molten iron and nickel, and the inner core is under so much pressure that it is still very hot, but is solid iron and nickel. The inner core in spinning and the currents of molten metal in the outer core creates a magnetic field. Iron and nickel are good at being magnets because they are 2 of the 3 ferromagnetic metals (cobalt being the 3rd). We aren’t sure why exactly this happens, because magnetism is a very complicated phenomenon, but we do know that molten iron spinning around can create a magnetic field, and this is happening in the Earth’s core, creating our magnetic field. Since the earth spins around its poles, the core spins in a very similar way (not exactly 1:1 correlation) which is why the magnetic poles match the Earth’s rotational poles (again not exactly 1:1, which is why we have true North and magnetic North being different things, magnetic North is in northern Greenland I believe)
Fun fact: the North pole if the Earth is actually a magnetic South pole. It got that name because when we made all of the definitions for magnets, we figured that the compass’s needle would have have North pole point towards North
Fun fact: we use the terms “north” and “pole” for magnets because we already used them for geography, and since compasses were how we figured out how magnets worked, the terms carried over
Fun fact: magnetic field lines must always form a closed loop, meaning all magnets must be dipoles. We have electrons, which are negative on their own, it’s an electric monopole, but there’s no equivalent for magnets. Every magnet has a North and a South.
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