 So now I look at Faraday's law. And this is going to help me figure out the average EMF. So in Faraday's law, they were looking at changing the magnetic flux through a wire loop. And what they found was that it induces an EMF in the loop. Remember, EMF is electromotive force. And that was kind of like the ideal voltage source inside of a battery. Well, how much EMF is induced depends on how fast the flux changes. Not the value of the flux itself, but just how fast it changes. So what's our equation for this? It's going to look like this, where EMF average is minus n delta phi divided by delta t. So let's take this one symbol at a time. Over here, my little epsilon again is my EMF. And the subscript of AVG tells me it's the average EMF. Over here, I've got the delta phi. I have to treat this as one quantity, not two things. And it's the change in flux. Similarly on the bottom, my delta t is the change in time. My n is the number of loops. Sometimes you'll see the equation without this, which means they're assuming just a single loop of wire. But if instead you had several loops of wire kind of all bound together, you'd use this for the number of loops. The minus sign in there is actually an indication of direction. And we're not going to be directly working with that right away. So let's talk then about this change in flux. Well, my change in flux could be written out in the standard way of what we mean by our delta, which is it's the final flux minus the initial flux. In general, the flux can increase, decrease, or stay the same. Remember, though, that if it stays the same, that means my delta phi is 0, so I have no EMF. The flux has to increase or decrease if I want to induce an EMF. So how do I change the flux? Well, there's three general methods. And if you look back at the equation for magnetic flux that we've already covered, it's pretty easy to see what those three methods are. I could change the magnetic field. I can change the area. Or I can change the angle. Changing any one of those three things will result in a change in flux. I could also change more than one at the same time, but most of our intro problems aren't going to have that. So that's your basic Faraday's law equation for the average EMF.