 In this video, we're going to be talking about Faraday's law and how we can use Faraday's law to determine the induced voltage that is going to be across a coil when it has a current rise or fall through it. So here we have a typical coil. We've just got a bunch of wire wrapped around, say an iron core. When we have current rise or fall through it, we have magnetic lines of flux being created. Magnetic lines of flux are going from north to south as they're apt to do. And what will happen is as current rises through this conductor and through this coil, it's going to induce a voltage. And we're going to use Faraday's law to determine what that voltage is. Same way if current falls, if we suddenly see current drop out of this circuit, we're going to get a voltage induced as well. Because what will be happening is our lines of flux are cutting conductors and when that happens, it induces a voltage. So let's take a look at Faraday's law. Here we have E, which is the induced voltage, is equal to negative L. That's going to be the inductance of the inductor. This delta I is going to be your change in current and delta T is the amount of time, the change in time that you're using. So let's throw up some examples of what we're talking about here. Let's say I've got an inductor and it is 300 mH. So it has an inductance of 300 mH. That's where we will put this in here. Now, you'll notice we don't actually have a negative in front of that. The negative is part of the formula because it will tell us whether or not the induced voltage will be helping the voltage that is the source voltage or if it will be opposing it. So that's what that negative stands for. And we'll talk about that in just a second here. Next up, let's say that we have three amps rising through this inductor. So it started at zero and we have three amps rising up through there. That'll be our delta T. It started at zero and it ends up at three. And so our delta I, sorry, is going to be three amps. Next up, let's say that all that that happens in is in 50 milliseconds. So that's in delta T. That's our change in time. So what we're going to do is we're going to take these numbers here and we're going to plug them up into our formula. We change the 300 millihenries into Henry's. That's why I have a point three three amps rising. That's a positive. We're going from a zero up. So that will be a positive three. And we convert the milliseconds 50 milliseconds into seconds, which is point zero five. Then we just plunk that into the calculator three divided by point zero five times point three negative gives us our answer negative 18 volts. Now it's important that we understand that that negative 18 volts means that this voltage is going to be opposing the source voltage is pushing back on it. And when we get into inductive reactance discussions, that's important to understand. So if this was three amps falling, let's say, then this would be a negative in front of a negative three here. Sorry, there would be a negative right there. Let me just draw that in there for you so I can get my point across. But I would have a negative in there if this said falling. So if there was current falling, that's negative three, then we do the calculation. We get the same number, but we would see that there'd be no negative there because as current is falling, the inductor would try to keep it up so it would be aiding the source voltage. So that is how we would use that formula. Let me just go ahead and get rid of those marks. And that's how you walk through our formula here of E is equal to negative L delta I over delta T. Just remember that your L is your inductance in Henry's. So if you're dealing with Miller Henry's, which is very common, you have to convert that to Henry's. Your I is your current and you have to determine whether that current is rising. If it's a rising current, it's a positive number. If it's a falling current, it is a negative number. And then our delta T is the amount of time that that happens in. And that's how you calculate out induced voltage using Faraday's law.