How does magnetism work?

A big thanks to @lostbetweenthelines for this subject. Check out her wonderful book 'you took your time'.

Everybody is familiar with magnetism. Magnets can pick up metal objects; there's a magnetic strip on credit cards; magnets are useful as locks; electromagnets are an essential part of an electric motor; a compass depends on the Earth's magnetic field; magnetometers are used to measure magnetic fields; magnets are used in speakers, earphones car horns and doorbells; music, speech and video can be stored on magnetic tape or on hard drives; magnetism is used to detect diseases in a magnetic resonance imaging device; and many more devices and instruments use magnetism. It's a phenomenon that has been around for a very long time, starting with the compass. The compass is an ancient instrument dating back to the Chinese Han Dynasty, and that's where it all started.

So, just what constitutes a magnet and how does it work? The first part of this question is easy. Almost all materials show some form of magnetism or are affected by it. There is ferromagnetism (iron, nickel, cobalt and its alloys), diamagnetism (opposes magnetic fields), and paramagnetism (most elements and their compounds). The affects of magnetism are the result of excess electrons in an element's outer shell. The explanation of this would require a longer dissertation.

As for the explanation of how magnetism works, that's where it gets crazy. First thing to remember is that Einstein's theory of relativity combines electricity and magnetism. That's why we call light and every kind of light-like radiation electromagnetic radiation. If you look at magnetism in its raw form it's an energy field that's projected out from the magnet and flows between the north magnetic pole and the south magnetic pole. This field is a force that affects other things that come near it, especially other magnets.

A magnetic field is the result of electrons in motion. Think of atoms or molecules as tiny spinning dipoles. Electrons flowing in the outer shells of atoms act like tiny electromagnets and when these tiny dipoles are combined you end up with a magnetic field. Take an iron rod and wind wire around it. When you pass a current through the wire you create an electromagnet, proving that electron flow creates a magnetic moment (a magnetic force in a specific direction).

Magnetic fields have polarity. There is always a north and a south pole. If you cut a magnet in half you end up with two magnets. The polarity remains and they repel if you try to connect the two north or south poles together. This is the result of the individual iron dipoles aligning in one direction. That's how magnetism is induced. A powerful magnetic field induces (forces) the iron dipoles to align so that their individual north and south poles are pointing in the same direction.

Quantum physicists talk about the electromagnetic tensor as an intrinsic property of moving electrical charges. A tensor is a multidimensional force vector applied to every point in space. An electron is a quantum particle and it has this tensor associated with it when it's moving. So, that's where this magnetic field concept comes from. I call it the magnetic ghost effect. It's like an aura, except in this case there are lots of equations to define a magnetic field and its strength in various directions.

One such equation is the Maxwell equation where the force F of a magnet is equal to the magnetic Induction B squared times the cross section of the pole in square meters A divided by two times the permeability of space μ. There are many more of these equations for magnetic effects.

Actually, the most important magnetic field is the one that protects the Earth. Without it we would not be here.

Thanks for reading.