Hey everyone, so in this video we're going to talk about how magnets work. We're going to talk about magnetic fields and magnetic dipoles. Let's check it out here. So remember that electric charges produce electric fields, and electric field lines that go from positive to negative charges. Like, if you have a charge that's by itself, a positive one, you're going to have electric field lines that go outwards like this. If it was a negative charge, then all these field lines would point inwards. Now if you have an electric dipole, right, when we have a positive and a negative charge, then you're going to have field lines that sort of go in arcs like this, but the electric field lines are always going to go from positive to negative like that.
Now similarly, magnets also produce lines. They're magnetic field lines given by the letter b, but they're directed from north to south on the outside. One kind of easy way to remember this is that almost everything in nature goes from high to low. So we have electric field lines that went from positive to negative and you can think of north and south as being positive and negative like on an axis or something like that. Right? So that's north and this is south. Alright? So what happens here is that you would expect the field lines to sort of look like this inside the magnet, but they're actually going to form loops that travel on the outside of the magnet. So you're basically going to go here from north and you're going to go in a loop around until you hit south and you're going to go in bigger and bigger loops like this.
Alright, so here's how the magnetic field lines work and look like for magnets. Alright, so you follow these sort of arrows like this and they always go from north to south. Now if you keep sort of going along this line here, what you'll see is that they actually sort of go from south to north on the inside of the bar magnet. So that's kind of important here. So I'm going to write here that it's south to north on the inside. Alright, so that's kind of important. Alright. So one key difference between electric fields and magnetic fields is that you could have single charges that could exist alone with electric fields. They were called electric monopoles. So for example, we just drew the electric field lines for a single positive charge and that's totally fine. So in other words, this is also known as a monopole. Right?
Now magnets on the other hand cannot just have one pole. That's really important here. Magnets, you can't just have a North or a South Pole. So magnetic monopoles cannot exist, only dipoles. And so in other words, magnets always have to come in north and south pairs. Now one important consequence of this is if you were to ever cut a magnet in half, I don't know why you would, but you would expect to see that a magnet would basically, turn like this. Right? You would expect that if you cut a magnet in half, it would sort of look like this at the end with a south and a north by itself, but that actually would not happen. This is wrong. Instead, what happens is if you split a magnet in half, you just end up with 2 smaller magnets. So if you cut a magnet in half, it would actually just look like this. You would have a south and a north, and then you would have a south and a north. Alright. So this is pretty much what would happen here. Alright. It's kind of a weird thing, but that's just the way that magnets work. Alright? Let's go ahead and take a look at our example here. So we're going to have both magnets that are fixed in place, but they can rotate about their central axis. Basically, you're going to hold these things in place here like with a pin, but they're able to freely rotate. Alright?
Now in the first thing, in the first part here, we're going to release only the bottom magnets. So in other words, the top magnet is going to remain sort of in place and it's going to look exactly how it did before. So in other words, it's going to be north and south and we're going to ask to find out what its new orientation would look like. Alright. So basically, if we kept this North one in place well, the top one, what would happen to the bottom magnet? How would it spin? Alright. So hopefully you guys realize that the way it would spin, is it wants to sort of orient itself so that opposites attract. So it's basically, what's going to happen here. So you're going to have this bar magnet, it's going to sort of line up with this. The key thing to remember is that opposites attract just like in electricity, right? It's positives with negatives, north with south, opposites attract. Alright. So if this is the south side, then what's going to happen is that this side here actually has to be the north side. So what's going to happen is you're going to keep this thing in place here and the bottom one's actually going to flip around like this and it's going to sort of orient itself so that the north side points to the south side. Alright?
Now let's look at part b here. Part b is a little bit tricky because it asks if you release both magnets simultaneously. So in other words, now both of them are able to spin, what's the new orientation going to look like? Alright. Well, hopefully you guys realize that unlike this first one here, now both of them are actually going to rotate and they're going to orient themselves in such a way that they point along towards each other. So the top one is going to rotate like this, the bottom one is going to rotate like this, so they're kind of like aligned like that. Now, what's tricky about this is that there's actually 2 different possibilities here. Alright? So they're going to sort of orient themselves like that. And one possibility is you could have north and south, and in this case what's going to happen is just like we had over here in part a, this one's going to have north and south. Or you also could have that you have the top and bottom magnet and basically you could have a situation where you could have the top magnet flips around and South becomes North. It's basically the opposite of this. And in this case, what happens here is that you have South and North. Right? Basically, just the opposites so that the opposites always attract here. So these are the sort of two possibilities you could have with these magnets. Alright folks. That's it for this one. Let me know if you have any questions.