Was last week’s electricity safety article enough of a break? Hopefully it was because I think my topic this week might break even me. The study of electricity falls under the immensely broad scientific category of physics. When we talk about it though, we usually refer to it as electromagnetism which is itself part of the four fundamental forces. These include the “strong” force (also called the nuclear force), the “weak electric” force (think subatomic particles), the gravitation force (what’s holding you to the earth right now), and finally the electromagnetic forces, which are of interest to us here. So far I’ve focused almost exclusively on the “electro” part of that topic but not so much on the “magnetism” part.
Electricity and magnetism are like two buddy cops in the best buddy cop movie ever. You might have noticed that I haven’t really discussed exactly how electricity is generated yet aside from a few hints about it, and that’s because it depends entirely on concepts within magnetism. I’m sure we all know about magnets. They’re just as relatable as electricity in many ways. There are magnets holding my car keys to my refrigerator as I write this. Magnets have a north pole and a south pole. Opposite poles attract and like poles repel. Nope, nothing about electricity yet.
So where do magnets come in? Well, surrounding every magnet there is a magnetic field. You might remember this being demonstrated in school with iron filings grouping themselves in a very specific pattern around a magnet. The filings group themselves along the magnetic field lines. When talking about these field lines in the context of interacting with them on any given plane, they will often be called lines of flux or magnetic flux. This is the key. These lines are what you need to generate electricity.
Imagine I have a simple rectangular bar magnet suspended on its center. I take a copper wire connected to am ammeter (a device for measuring current) and I pass the wire straight past the end of the magnet (north pole or south pole, it doesn’t matter). The ammeter needle will briefly wiggle indicating that a current was present. The current in this test is very small, and it only occurs for a brief moment, but it is there. How did this happen? When a conductor cuts through a line of magnetic flux, the electrons in the atoms of the conductor are compelled to move. How exactly are the electrons compelled to move? At that level, you’ll have to read up on it yourself as it’s totally beyond a short article here, but it is covered under the field of quantum electrodynamics. Have you ever heard of Richard Feynman? Quantum electrodynamics was his playground (one of many actually).
Ok, so if we abstract away how exactly the electrons are compelled to move and just accept that they do, we arrive at the conclusion that cutting through lines of magnetic flux with a conductor creates a current. In my example, we used one magnet and a single copper wire. To generate more current, you need to cut through more lines of flux. You can do this by adding more magnets (to increase the flux), more conductors, or both, which is what we generally do. This whole theory of cutting lines of magnetic flux is the operating principle behind every generator (direct current) and alternator (alternating current).
In a basic alternator (yes, just like the one in your car) there is a circular casing that holds coils of conducting wire. Why coils? Again, more wires, more lines of flux cut. Coils also help to concentrate the lines of magnetic flux. Basically the purpose of every single design element is to ensure that the most lines of magnetic flux are cut for a given area. The fixed outer area with the coils is called the stator. The inner area that rotates is called the rotor, and in our example here, it simply contains spinning magnets. Each time a pole of the spinning magnet passes one of the many coils in the stator, a current is generated. By having enough coils covering all radial angles, the alternator will be generating a current during pretty much it’s entire rotational cycle, though the current will be alternating. Typical alternators don’t use permanent magnets on their rotors. They actually use electromagnets, but the theory of operation is exactly the same.
Once again, I’m out of space to continue about all of this here. The reason I went into this topic was so that in subsequent weeks I’ll have a foundation to talk about electromagnets, multiphase power, induction motors, and some other high-level interesting stuff that just won’t make sense if you don’t have an understanding of the fundamental interactions between electricity and magnetism.