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Current time:0:00Total duration:10:44

Video transcript

we've learned a little bit about gravity we've learned a little bit about electrostatics Oh time to learn about a new fundamental force of the universe and this one is probably second most familiar to us next to gravity and that's magnetism magnetism where does the word come from well they actually I think several civilizations I'm no historian found these lodestones these objects magnetism magnetism these objects that would attract other objects like at other magnets or would even attract metallic objects like iron ferrous objects and they're called lodestones that's I guess the Western term for it and the reason why they're called magnets is because they're named after lodestones that were found near the Greek province of magnesia magnesia and actually think the people who lived there were called magnets but anyway let's let you could Wikipedia that and learn more about it than I know but anyway let's let's focus on what magnetism is and I think most of us have at least a working knowledge of what it is in terms you know we've all played with magnets and we've dealt with compasses but I'll tell you this right now what it really is is pretty deep and I think it's fairly I don't think anyone has we can mathematically understand it and manipulate it and see how it relates to electricity we actually will show you that the electrostatic force and the magnetic force are actually the same thing just viewed from different frames of references I know all of that sounds very complicated all of that but in our classical Newtonian world we treat them as two different forces but what I'm saying is although we're kind of used to a magnet just like we're used to gravity just like gravity is also fairly mysterious when you really think about what it is so is magnetism so with that said let's listen please try to get some working knowledge of how we can deal with magnetism so we're all familiar with a magnet want it to be yellow I can make the boundary yellow no I didn't want it to be like that either so if this is a magnet we know that a magnet always has two poles it has a North Pole and a South Pole and these were just labeled by convention because when people first discovered these lodestones or they took a lodestone and they magnetized a needle with with that lodestone and then that needle they put on a cork in a bucket of water and that needle would point to the Earth's North Pole they said oh well the point the side of the needle that is pointing to the Earth's north let's call that the North Pole and the point of the needle that's pointing to the South Pole the sorry the point of the needle that's pointing to the Earth's geographic South we'll call that the South Pole or another way to put it if we have a magnet the direction of the magnet or the side of the magnet that Orient's itself it's allowed to orient freely without friction towards our geographic north we call that the North Pole and the other side is the South Pole and this is actually a little bit if you know obviously we call the we call the earth we call the top of the earth the North Pole you know this is the North Pole north pole and we call this the South Pole and magnet and there's another notion of magnetic north and that's where I guess you could kind of say that is where a a a a compass the north point of a compass will point to an actually magnetic north it moves around because we have all of this moving fluid inside of the earth and a bunch of other interactions it's a very complex interaction but magnetic north is actually roughly in northern Canada so magnetic north might be here so that might be magnetic north and magnetic south I don't know exactly where that is but it can kind of move around a little bit it's not in the same place so it's a little bit off the axes of the geographic North Pole and the South Pole and this is another kind of slightly confusing thing is magnetic north is kind of the geographical pation we're a north where the north pole of a magnet will point to but that would actually be the South Pole of if you viewed the earth as a magnetic as a magnet so if this was if the earth was a big magnet this would you'd actually view that as the South Pole of the magnet and this and the geographic South Pole is the North Pole of the magnet you could read more about that on Wikipedia no it's a little bit confusing but in general when most people refer to magnetic north or the North Pole they're talking about the geographic north area and the South Pole is a geographic South area but the reason why I make this distinction is because we know when we deal with magnets just like electricity although or electrostatics but although we'll show it of key difference very shortly is that opposite poles attract so if this side of my magnet is attracted to Earth's North Pole then Earth's North Pole or Earth's magnetic north actually must be the South Pole of that magnet right and vice-versa the South Pole of my magnet here is going to be attracted to Earth's magnetic south which is actually the North Pole of the magnet we call Earth anyway I'll take Earth out of the equation because it takes a little bit confusing and we'll just stick to bars because that tends to be a little bit more consistent let me erase this let me there you go I'll erase my magnesia I wonder if the element magnesium was first discovered in magnesia as well probably and I actually looked up milk of magnesia which is a laxative and it was not discovered in magnesia but it has magnesium in it so I guess it's roots could be in magnesia if magnesium was discovered in magnesia anyway enough about magnesia back to the magnets so if this is a magnet and let me draw another magnet actually let me erase all of this when I go on the tangents I just all right so let me draw two more magnets that's one magnet that's another magnet we know from experimentation when we were all kids this is the North Pole this is the South Pole that the North Pole is going to be attracted to the South Pole of another magnet and then if I were to flip this magnet around it would actually repel north to North facing magnets would repel each other and so we have this notion just like we had in electrostatics that a magnet generates a field it generates this these vectors around it that if you put something in that field that will that can be affected by it it'll be it'll be so there will be some net force acting on it so actually before I go into the magnetic field actually want to make one huge distinction between a magnet and or between magnetism and electrostatics magnetism always comes in the form of a dipole what does the dipole mean it means that we have two poles a north and a south and electrostatics you do have two two charges you have a positive charge and a negative charge so you do have two charges but they could be by themselves you could just have a proton you don't have to have an electron they're right next to it you could just have a proton and it would create a positive electrostatic field right in our field lines or what a positive point charge would do and it would be repelled so you don't always have to have an electronegative charge there similarly you could just have an electron and you don't have to have a proton there so you could have mono poles these are called mono poles when you just have one charge when you're talking about electrostatics but with magnetism you always have a dipole if I were to take this magnet this one right here and if I were to cut it in half if I were to cut it in half somehow miraculously each of those halves of that magnet will turn into two more magnets where this will be the south this will be the north this will be the south and this we'll be the north and actually the theoretically I've read my my own abilities don't go this far there could be such a thing as a magnetic monopole although it has not been observed yet in nature but so everything we have seen in nature has been a dipole so you can just keep cutting this cutting this up all the way down to if it's just one electron left and it actually turns out that even one electron is still a magnetic dipole it still is generating it still has a North Pole and a South Pole and actually turns out all magnets there the magnetic field is actually generated by the electrons within it by the spin of the electrons and that you know when we talk about electron spin we imagine you know some little ball of charge that's spinning but electrons are you know it's hard to they do have mass but it it starts to get fuzzy whether they're energy or mass and then how does it ball of energy spin etc so it gets very contem very almost metaphysical so I don't want to go too far into it and I frankly I don't think you really can't get an intuition it is almost you know it is a realm that we don't normally operate in but even these large magnets you deal with the magnetic field is generated by the electron spins inside of it and by the actual magnetic fields generated by the electron motion around the protons well I hope hope I'm not not not overwhelming you and you might say well how come sometimes a metal bar can be magnetized in hot sighs sometimes it won't be well when a when all of the electrons are doing random different things in a metal bar then it's not magnetized because they're the magnetic spins or the magnet the the magnetism created by the electrons are all cancelling each other out because it's random but if you align the spins of the electrons and if you're aligned their rotations then of then you will have a magnetically charged bar if anyway I'm past the 10-minute mark but hopefully that gives you a little bit of a working knowledge of what a magnet is and in the next video I will show what the effect is well one I'll I'll explain how we think about a magnetic field and then what the effect of a magnetic field is on an electron or not even electric on a moving charge see in the next video