#electrical transformers

Quick initial bit of info you need to know: Electrical power flowing through a conductor has a few primary related characteristics: voltage, current, resistance, and power. Voltage is "how much push" the electricity has. Current is kinda like "how fast it's moving", resistance is, well, resistance: it's how much the wire resists having electricity go down it. Voltage and current combine to form power. There's the same amount of power in a high-current low-voltage flow of electricity as a low-current high-voltage one. (think of it like a fast-flowing water pipe vs a slow-flowing creek. Because the slow one has much more volume, it manages to move the same total amount of water)

So when you put electricity down a wire, you are also heating up the wire, because the wire is not a perfect conductor (unless it's a superconductor, but at the moment that requires cooling it a lot, so we don't do that outside of like MRI machines and cool physics experiments). Most of the time we don't want Hot Wires, we just want electricity to get places. (unless we're making a toaster or an oven, then we DO want hot wires). But it would be a huge waste if we had a powerplant and most of the electricity never got to all the things we need to power because we were just making the wires hot. But there's a trick to avoid this:

So the amount of energy lost to heating is proportional to the current going through it. (It's actually the current squared times the resistance). But the important thing is that low-current = low loss, high-current=high loss. So we just need low-current power lines!

But wait, don't we need current? you need a bunch of current to run things like dryers and electric ovens and so on.

yes. But we don't need to TRANSFER the power using high current. Because here's the thing, voltage and current are related. Thanks to Georg Ohm (no relation to the spiders guy) and Ohm's Law (current = voltage divided by resistance) (plus a side of Kirchhoff’s Voltage Law), you can take a given current and lower the current by increasing the voltage. So we just need high-voltage power lines, and they'll be low-current, and therefore low-heating-loss. Then once it's in your house, we turn it back into low-voltage high-current, and now it's Powerful and can run your dryer or oven or whatever.

But how do we change the voltage of a current? TRANSFORMERS, THAT'S HOW!

So the basic idea of an electrical coil is that as the current in the coil changes, this generates a magnetic flux. To simplify: changing current + coils = magnetism. This is handy when we're building motors, because this is how they work: It's basically a magnet pulling itself around and around in circles.

But wait how do we get changing current? isn't the current coming down the line from the power station constant?

Nope! It's AC current: Alternating Current. This means that instead of a continuous current coming down one wire and going out the other, it's constantly changing direction, 60 times a second. It's a sine wave, it goes positive, then negative, and repeats. So the current is always changing, and if you run it through a coil, it'll create a magnetic field one way, then the other, over and over.

Well that's nifty and all but how do we use that for anything?

So it turns out the whole idea of "a changing current in a coil causes magnetism" is reversible, it works both ways. A changing magnetic field causes a change in current in a coil.

So what if we took our coil and put it next to another coil? Maybe with something in between (a "core") that conducts the magnetism, like a piece of metal?

Well then you put a changing current in one side, and you get a changing current out of the other side! Nifty. But also useless. You got out pretty much the same thing you got in, minus some losses due to heating and magnetism and such. (It's not actually useless: this is an isolation transformer, and can be used for safety reasons)

But here's the next trick: Conservation of energy. You put in a given amount of power, you create a given amount of magnetism, and that magnetism gives you a given amount of power back. Other than some small losses, it all balances. It has to, or the universe wouldn't work, and would explode.

But you what I'm describing here is a perfectly symmetric transformer. What if you had more windings in your coil on one side than you did on the other side?

Well, it turns out that the voltage you get out of a transformer is related to how many turns you have in the output side compared to the input side. So if your input side has 200 turns of a coil, and your output side has 100 turns of a coil, your output voltage will be twice the input voltage. And you can swap this around to make the output voltage half the input voltage.

The current will of course adjust to match. Twice the voltage means half the current.

And now you see how we can make powerlines work. We have our powerplant generate high voltages, then run those super-high voltages (in the range of 100,000-800,000 volts) down huge raised power lines. When they get to an area that needs power, we have a bunch of transformers that lower them to a distribution voltage (somewhere in the range of 5,000-10,000 volts), which runs to a transformer on a pole near your house, which lowers it to the standard 120 volts (in the US. most of the rest of the world uses 240 volts), which is provided to all the outlets in your house.

Then you plug a power supply into those outlets, to run your computer or power your phone, or whatever. Guess what's in there? Another transformer! It lowers the voltage even further, so it'll be 12 or 5 or whatever the device needs. (It also rectifies it into DC power, because computers run on DC, not AC. But it does this after changing the voltage, because it's easier to change the voltage of AC power than DC power).

So it's transformers all the way down.

FINAL BIT OF NEATNESS WITH TRANSFORMERS:

So remember how I mentioned that they're two coils, around a core of metal? Well... you don't need the metal, technically. It helps, yes, and makes them more efficient, but you could just use air. Magnetism can go through air or plastic or all kinds of stuff without being stopped. It's less efficient, sure, but it works.

So what if we then took advantage of this? We build two half-transformers. One in a device that plugs into the wall, and another into some device that needs power, like... a phone! Normally these coils will do nothing, because they're not a complete transformer, as the other coil is nowhere near it.

But if you put the coils near each other, they'll start interacting magnetically. They become a transformer. Power is transferred from one side to the other, through the magnetic field, and now your phone can wirelessly charge without wires!