28. Magnetic Fields and Forces
Magnets and Magnetic Fields
How Magnets Work Concept:
How Magnets Work
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Hey, guys. So now we're gonna start talking about magnetism. And in this first video, I'm gonna keep it really simple and briefly explain to you how magnets work. Let's check it out. All right. So a long time ago, we found out that there's some metals that will sometimes attract each other. They sort of magically get stuck. And this was first found in the Greek island of Magnesia. So these magic medals were called magnets Magnets. The metals that are most commonly that most commonly have this magnetic property off getting stuck to each other are armed, cobalt and nickel. But you should know that not all pieces of iron, cobalt and nickel are always magnetic. Okay? Electricity and magnetism are very similar. There's a lot of analogies we're gonna draw between the two. The first one here is that forces electric forces can only exist between charge materials. Many if you have two objects thanks to each other, they're only going to interact electrically if both of them are charged. If they both have charges, same thing with magnetic forces. So you're gonna have magnetic forces if the two objects have this magnetic property. So if you have two objects close to each other that are non magnetic. You get no force one magnetic and one non magnetic. You get no force and Onley. In a situation like this, you're going to get a magnetic force. Very straightforward. Remember also that electricity in electricity the forces could be attractive or repulsive. The same thing is gonna happen with magnetic forces between magnets, depending on the ends of the magnets. Okay, so let's say you have an iron bar here and then you have another iron bar here. And when you bring them close to each other, they are attractive. They attract each other, there's an attractive force. Now let's say you flip, you get the second bar and now you flip it. Now you flip that bar and then you see that this force is actually now repulsive so these guys will repel each other. And just from this observation, you can you can conclude that there must be two different types of sides. Okay, because the two sides are behaving differently. There must be two types of sides which they're called magnetic poles. So a poll is just one of the sides off the bar. So we could do something like, Let's call this side A and B And then here we flipped. And then this is going to be be and a So that's the first thing you need to know about magnets is that they have two different sides. Okay, now, in electricity, these sides were called you had positive and negative charges, and in magnetism, these sides are gonna be called North and South. Polls poll again. It's just a word for side or end of the magnet bar. You may remember that these names are arbitrary, positive could have been called good and negative could be called evil or yellow or blue or whatever. But that's what they chose. And same thing with north and South. This could have been called the positive side. Scooting called the negative side, but they chose north and south. So those are the names, and the last thing I want to talk about is what happens if you get two medals. Two magnets that are identical. So these guys here are same as left. What happens if you face different faces, different ends of the metals. So if you were to get to two magnets and do this experimentally. What you would see is that if you have the a side with the A side, these guys would repel each other. But then, if you flip this and then you have the A end or the A pole with the beep hole, they would attract if you flip both, so you have DNA, they would also attract. And finally, if you had B and B, they would repel. So hopefully you see a pattern here, which is that whenever the whenever the sides are different A and B being a, they will have an attractive force, and you may remember this from electricity and electricity. Opposite charges would always attract similarly in magnetism. Opposite Poles will also attract will also attract cool. So the saying that opposites attract holds true for both electricity and magnetism. And that's it for this one. Let's keep going
Magnetic Fields and Magnetic Dipoles
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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.
Compasses and Earth's Magnetic Field
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Hey, I saw in this video we're gonna talk about Compass is and the Earth's magnetic field. Let's check it out. All right. So remember, magnets have ends or sides or polls. They're called north and south. So something like this this and is north s and the South. But how do you know which one is which? How do you know which one toe label north, for example. Well, the end of the magnet that points to the Earth's north is the one that gets labeled to be the North Pole. Off the magnets, let me show you. So the Earth's north pole somewhere around here, the South Pole. Somewhere around here, it's actually angles because the earth spins around a tilted axes. Okay, so the earth spins around that little line there. Um, this is the North Pole, which, by the way, it's just a bunch of water on Ben. This is the South Pole, which is a bunch of ice and Antarctica. Andi, you have sort of like the equator over here. So the way this works is let's say you have a magnet and it has a paint one side red, and then you paint one side blue. And then you bring this over here and you're in the US somewhere. And you notice that when you're here, this thing always orients itself like this with the red side this way and the blue side this way. And then you move over to Europe over here, and then you notice that it always orient itself with the red side pointing to north and the blue side pointing the other way. So what you're gonna do you gonna say? Well, this one is pointing north. Red is pointing north, so the red side must be what we're gonna call the north side. Okay, So north and South, this is completely arbitrary. They could have done it backwards. They could have been the other way around, but they decided to say, Hey, if it points north, we'll call it north. That makes sense, right? Uh, and that is, by the way, how compass is work. Okay, so this is what a compass looks like. It has a magnetic needles, a very thin metal, very tiny metal inside that is magnetized. And the end of that needle, um, that points to the Earth's north is labeled north. Okay, so you can't see here, but this is north right there. Okay? And you may not be able to see this, but this tip is red. Okay, so on old school magnets, one side is red and the red side is the one that is not the north side off the needle. Okay, The north side of the needle, By the way, sometimes if you don't have colors, you may see this as an arrow. You may see something drawn like this. So, for example, here, I could have drawn if I had something over here. I could also have just made an arrow this way, which means that that is the direction off north. Okay, By the way, if you have a magnets here that's pointing directly north, it means that you're probably somewhere close to this line so that it's pointing straight up, OK? And similarly, if you had a compass that the north that the north arrow or the north side of the magnet was pointing that way, it means that you're probably somewhere over here. So this is why compass is air able to be used, are used to be used as navigating devices. Cool. So if it points north. It's north. That's that's another important thing to realize is remembering that magnetic forces can only exist between two magnets. Okay, we can only exist between two magnets or more generally between two things that are magnetized. Okay, So if this needle here is attracted to the top of the Earth, if that needle is attracted to the top of the earth and you can only have attraction between two magnets, it must be that not only the needle is a magnet, which it is, but that the earth is also a magnet, which it is. So the Earth. It's not a magnet in the typical sense that there's a a huge metal bar through it. But it behaves like a magnets. A gigantic magnets. Okay, so you can think of the earth as as though it had a huge metal magnetized metal bar. Um, this way so that things can be attracted to its north. Okay. All right. So that's the first thing. Cool. So the earth is a magnet. Weird. The second thing is, if you realize that opposites attract and the compass is north points to the Earth's north. So let's do that slowly Let's say I have a compass here. And the north of the compass is pointing towards the north of the earth. Remember, opposites attract. So if this end is attracting this end and we call this north, this must be south. Okay, this must be south now. You might be thinking. No, that's north. We just said it. That's north. Well, this is the what we call the geographic north. Okay, Which one way to think about this is that it's up there on the map. It's on top of the map. Okay, that's the locational, the geographic north. But it must be the magnetic south, meaning the earth behaves like a magnets that has its north over here. And it's south over here. So the thing is, if we wanted to call these magnets, um, this side of the magnet north because it's pointing to the north of the earth, we must then recognize that this has to be called the south side of this big, imaginary magnet that sits inside of the earth. All this stuff is just convention, but that's how it works. Okay, so north and south. So please get that difference down. And because of this the north pole of the needle. So here's the compass needle. The north won the arrow. This is the north side or end of the needle is also sometimes called south seeking and again it's because opposites attract. So if you are the north, you want south. So if you're south you are a north seeking magnets for your the north seeking side of the magnets. Um, in that case, quote another very important but general point is that any magnets north is always going to point in the direction of the magnetic field around it. So what does that look like? So I want to redraw the earth over here. Onda, we're gonna draw the magnetic fields on the earth so the top of the earth is gonna be the South magnets and the north magnet the bottom. Remember, magnetic fields go from north to positive through the outside, hide alot on the outside. It's gonna look like this high to low, high to low, like that right north to south on the outside. So the magnetic field lines will look like this. Um, any magnets north will points in the direction of the magnetic field around it. so if you had a magnet right here or a compass, it will point exactly in this direction here. Okay. Exactly. In this direction here, that means that if you have a magnets, um, if you have lets the different color. If you have something over here, it's actually going to point like that. Okay, um, but then you wouldn't really be navigating. Now you run out of space, but just to make the point that not now you got bigger problems, right? Um, but just make the point that it's always going to follow this line, so it actually doesn't always directly point north. Right? If you're here, if you're on the equator right here, it's actually going to sort of go up like this. It doesn't really point north directly. Depends on where you are. So you have to sort of adjust for, um, your sort of height on the earth. Okay. Similarly, if you look here, it actually points. If you draw it down here, it actually points away. It doesn't point towards the north of the Earth. What it actually does is it points away from the south. Okay, so that's the last point. I'll make and then we'll do a quick example. So it says here if you by the way, if you notice in these examples I was careful. Toe always draw stuff on the Northern Hemisphere. But if you are on the south of the Earth, if you are here on the Southern Hemisphere, then the compass is south. Poll will points to the Earth's South poll, which, by the way, this is our geometra, our geographic south, which will be our magnetic north lips, not Morris North. Okay, so to wrap it up in the very beginning, the video, I said the north side of a magnet points towards the north of the earth. But actually, if you learn Southern Hemisphere than the south side of the magnet points towards the south of the Earth. The easiest way to remember this it's just remember how what the lines look like. And remember this one statement here that's the direction of the magnetic fields or the direction of the magnets North is always going to follow the blue lines. Okay, let's go quick example here. So the green magnet bolos fixed in place and you have a ton of small compass is looking around it. We want to draw approximate orientation of the needles. Um, and we're gonna use an arrow to indicate the north direction. So what we're gonna do here is we're gonna first draw. We're gonna use this principle right here, which is super important. That's the north will points in the direction of the magnetic fields. So what is the direction? The magnetic fields? Well, magnetic field is always north to south through the outside. So I'm gonna do north to South like this. And then I'm gonna be very careful to do this here. Obviously, I laid out these guys there for a reason. So it all just looks real cute. And it looks like that you can't really see the last one. But that's cool. So north to south. So it looks like this north to south. It looks like that quote. So that means that this needle here is going to be pointed. This needle here is going to be pointed in the direction of the field lines so the needle is going to point like this. This needle is going to point like this. This needle is going to point like this. This needle is going to point like this. And then finally this needle is going to point down right there. The reason we said approximate is because it depends on how precisely you draw this thing. I just wanna make the point super important that the fields, the direction of north on a magnet will follow the direction of the fields. And by the way, this works in any hemisphere. Cool. That's it for this one. Let's get going.
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