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Anderson Video - Faraday's Law

Professor Anderson
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I should just have a whole bunch of, like, stick on things, right? So I could just do my little emoticon right there. [inaudible] Okay, yeah. Let's go back to, uh, let's go back to Faraday's Law for a second. Okay, the reason that you care about flux is because when you have a current loop. When you have a loop that can generate current in it, it depends on how much flux is going through it. But it also depends on how quickly that happens. So Faraday's law tells us. That the EMF generated, remember EMF is like a voltage. It's the electromotive force. It's how hard is that thing going to get pushed, those charges, how hard are they going to get pushed? It is negative Delta Phi over Delta t. Okay. So this is kind of cool because if I just take a B field and I just have it pointed in one direction. And now, I take a current loop and I spin it at some frequency, Omega. What happens in this loop? What happens is, when it's facing one way there is current generated one way. When it flips around and goes the other way, there is current generated the other way. So this will actually generate an AC current in this little loop. Current's gonna go one way and then later on it's gonna switch and go back the other way. And it will keep sloshing back and forth between those two. And we can understand that from this idea of flux. Flux was positive in one direction and then the loop flipped around and so now it was negative and then it keeps going, it flips back to positive and so forth. But, let's say we do this with more than one loop. I don't want just one coil, I want a whole bunch of coils. In that case, we just add up the EMF, which is kind of like adding up the voltages. You throw an N in there to tell you that you're going to get N times the EMF that you would have with just one coil. Okay, so if we have a whole coil here, let's see if we can draw this. There's a whole stack of coils and now as it rotates in this B field it's going to generate an AC current. We know that it's going to generate it sinusoidally because it's rotating around at Omega.