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Magnetic Fields and Magnetic Dipoles

Patrick Ford
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Hey, guys. So in this video, we're gonna talk about how magnetic fields work. Let's check it out. All right. So you may remember that electric charges produce electric fields, they radiate these electric field lines, and it looks something like this. If you have a positive one, the electric field lines will radiate outward like this. And if you have two of them, they're going to radiate from positive to negative. So the electric field lines will look like this. And obviously there's a bunch. I'm just gonna draw a few. Well, magnets, just like charge is electric charges also produce a magnetic field, and this magnetic field is going to be from north to south. And one easy way to remember this is that everything or almost everything in nature is from high to low. You can think of positive as being high and negative is being low. And you can think about north as being high and south as being low. Okay, now, it's important to note here is that these field lines are going to be north to south on the outside. So what does that mean? It means that it looks like this You're gonna start from north and go to South. But it's not this way. It's through the outside, so it's gonna look like this quotes. He draw these little lines and there's one down. There's a bunch down here also, right, and they're going to look like that. What this means is, actually, if you keep following the loop, the magnetic field lines on the inside are actually south to north. So let's write this here that this is a south to north on the inside. Okay, so high to low on the outside. Cool. One key difference, however, between charges between electricity and magnetism is that you can have a single charges. Single charges can exist on their own. And this is called an electric Monta. Paul, right. Just like here, this guy can't exist without there being a negative charge in nearby. Um, this is not the case for magnets. Magnets cannot have just one poll. You can't just have the north pole of the magnet. The North Pole always has to come with the South Pole, which means that magnetic Monta polls cannot exist. Okay, so that's just the important conceptual point for you to remember. You can only have magnetic die polls. In other words, magnets always exist in pairs of north and south pulse. One consequence of this is that if you were to cut a magnet in half, I don't know why you would. But if you were to cut a magnet in half, right, it's pretty common physics problem. What you get is something like this. You would get that the new half the two halves will have both a north and a south north and a south, and they will be in the same direction as they were before. So here's the North is on the right side. Uh, therefore here the North's will be on the right side as well. Okay, Somehow they end up that way. Cool. Now let's do a quick example here, and it's a supposed both magnets below are fixed in place, but but are able, but it each is able to rotate about its own central axis. So imagine you have a little pin here and there fixed to this thing. So it's kind of like this right where I'm holding this. But let's say this is able to spin around its central axis like this. Okay, They're initially held in the positions below. So you hold them down so they can't move, um, in their magnets. And then you release the bottom one and we want to know what is the new orientation that it's going toe have. So, this one, you're for part A. You're holding the top one. So the top one has to stay like this north south. But then you release the bottom one. And what it's gonna do is because magnets attract the bottom one will move so that it's being attracted to the top one. And the key thing to remember here is that opposites attract. So if the bottom one is allowed to move, it will orient itself in such a way that it points towards this magnet. But the south side will be over here. OK, so it's actually gonna flip so that the south side is closer to the north. This one doesn't change because it's being held. Okay, it's fixed, and this one is free to rotate, so it orients itself that way. Now, what if you release both magnets simultaneously? Well, actually, this is a little bit of a trick question. Um, but think about what you think this what it might look like? And the reason I said it's a trick questions because there's actually two possible outcomes if you release them simultaneously. First of all, the most important thing is that you figure out that they would have to look like this, right? So you can think of this as as one. The bottom guy is gonna do this, and then this one's gonna do this. So they're gonna kind of meat in the middle and align themselves like that. That's important. The other thing is because opposites attract If this is north, this is south. This would have to be south, and this is would be north. The tricky part is that it could actually also have looked like this. Okay, It could also have looked like South here in the north here. So the inverse there or the opposite direction, and then this would've been north in south. Okay, if you release them simultaneously, they could have flipped either way. All right. And by the way, this is just to wrap it up here. This is how compass is work where they have a piece of magnets off magnetized metal that is on a little pin, and it's free to rotate on bond and points in whatever direction it should cope. That's it for this one. Let's keep going.