hey everyone hope you're all well I miss you lots but we'll keep soldiering through and learning physics it's gonna be great so then let's start talking about magnetism some of the basics of magnetic fields as well as electromagnetic fields so a little bit of background information that you probably already know from your your elementary school days maybe all bar magnets have two poles North Pole and South Pole so electricity we had positive charges and negative charges and magnetism we have north poles and south poles and then how those poles in Iraq depends on what combination of poles we're trying to interact with each other so if we have two light poles so two north poles or two south poles they will repel whereas if we have an opposite pole pairing a North Pole and a South Pole they will tend to attract now here's kind of a fun one that hopefully you don't have first-hand experience with if you take a bar magnet like this one it's got the North Pole and the South Pole if I were like crazy strong and angry and I broke it in half I would have two fully formed magnets each with a North Pole and a South Pole it would be impossible like I wouldn't break this and have like one piece that's just a North Pole and one piece that's just a South Pole each of those pieces would have both a north and a South Pole and that's because magnetic poles always come in pairs you cannot have a North Pole without an accompanying South Pole and that's actually a subject of a lot of interest in the physics community and a lot of research that's being done just trying to figure out like can we have magnetic monopoles is it possible to have a North Pole by itself and so far I don't think we found it it hasn't happened yet so so yeah magnetic poles always come in pairs um now one thing that we know about magnets then we know that they then can exert forces on each other because we talked about repulsion and attraction between these different poles and if we look at what those forces do we can see that those forces can happen at a distance magnets don't only attract or repel each other when they're in physical contact they don't even have to be touching to have that that attraction or repulsion take place which tells us that magnetic forces are field forces now previously when we have talked about fields we've looked at gravitational fields which all pointed radially inward and then electric fields which point radially inward for negative charges and radially outward for positive charges by convention so with that sort of foundation in mind let's make the jump over to magnetic fields which look a little bit different from these two so um first of all by convention the same way that electric field lines show us the direction of force on a positive charge magnetic field lines show us the direction of force on the North Pole of another magnet so like the north side of a compass which way it would tend to point that's what the field lines are telling us um and when we want a short hand magnetic field the variable we use is B and I don't know why maybe there is some language where magnetic field starts with a B or maybe we're out of letters I don't know but B means magnetic field okay so um so we're seeing that these field lines represent the the force on the north side the North Pole all right and so if we were to trace out that field for a permanent bar magnet what we find is that those field lines always form closed loops and the direction that those loops point because like poles repel and opposite poles attract is those those loops always point where they are the the field lines are pointing away from the North Pole and then back toward the South Pole so the image you see here is just kind of the way that iron filings would kind of tend to align to the magnetic field but if we actually want to put directions on those field lines they might look something like this so notice that for each of these magnets we're getting these circles these loops that are being produced and if we trace the direction of those loops the field lines are all pointing out of the North Pole of the magnet they're all pointing away from the north and then they loop back around in towards the South Pole now I just said that magnetic field always form closed loops that's not readily evident from these drawings because we're sort of limited in terms of like the amount of available space and we're limited to two dimensions but it turns out if you were to continue following those field lines around they do in fact like continue back around and connect back up from the north to the south so even though you can't see that all of these these field lines sort of out on the ends they're continued around and formed closed loops they do in fact do that um I also want to kind of trace this out for you a little bit in three dimensions cuz in magnetism we're gonna be thinking in three dimensions a lot and we're sort of limited in drawings to two dimensions so I want you to imagine for a moment that this little little box is a bar magnet kind of like what you see on the right in the images right here where we've got the North Pole up on the top here and the South Pole down on the bottom so if we have this three dimensional bar magnet and we want to see what its magnetic field looks like it actually looks something kind of like this it's kind of like doughnut shaped right so we've got these closed loop field lines circling all the way around our bar magnet in three dimensions again pointing out of the North Pole and back into the South Pole the other thing that you can't see from this is that really those magnetic field lines would be like a bunch of nested Donuts so we've got like our one slinky here but if you imagine like another bigger slinky that goes around this one and continues around and then an even bigger slinky that goes around them and continues all the way around and in 360 degrees that's really more what this magnetic field looks like it's just tons of like loops within loops within loops within loops extending all the way around and then going out like infinitely far so that's a fun thing to ponder anyway so that's what our our magnetic field looks like now just to take a moment to check your understand and consider this bar magnet right here where is the North Pole located now again a magnetic field lines always point out of the North Pole and then back into the South Pole so then looking at this I can tell that the bottom must be the North Pole of this magnet because that's where my field lines are pointing away from the bar magnet and then the top is the South Pole because that's where the field lines are pointing back in now bar magnets are good and cute um but there's more to magnetism than just bar magnets as you saw in your investigation an electric current also creates a magnetic field which means all this time that we've been building circuits we've also been building magnetic fields the entire time like any time we had a current there was a magnetic field around it you just didn't know all right so um electrical currents can also create magnetic fields even in the absence of bar magnets and so to try to like connect these two things together what I want you to think about is that all magnetic fields are really caused by the movement of charged particles and typically those charged particles are electrons so if we think about a bar magnet and what's going on down at the atomic level in that bar magnet each of the atoms in that magnet has electrons that are orbiting around this nucleus it's those electrons that are creating the magnetic field of the bar magnet it all comes down to the way that the electron is orbiting around the nucleus of its atom way down in that magnet and then similarly when we get an electromagnet or this this current carrying wire that produces an electric field or excuse me a magnetic field um that again is caused by the movement of electrons in the form of a current going through that circuit so whether we're talking about bar magnets or we're talking about current-carrying wires and electromagnets in both situations those magnetic fields arise from the movement of the electrons while all right so to kind of focus in a little bit more on what that means for bar magnets all right so just to provide a little bit of context in unmagnetized objects atoms will tend to cluster together and form these little groups which we call domains and those domains um will have the electrons starting off just orbiting random okay and as a result we don't get an overall magnetic field because one domain might have a magnetic field that's sort of like pointing this way another magnetic field for another domain is pointing this way and another one's going that way so they're all kind of cancelling each other out there's no unity there's no organization so the magnetic field just doesn't really get anywhere all right but if we were to magnetize that object what that really means is that we're getting all of our electrons in alignment so they're all orbiting around their nuclei the same way and that causes the domains to all have magnetic fields that are all pointing in the same direction and then all those magnetic fields kind of build and add together and that gives us an overall magnetic field from that object now most materials their domains don't naturally tend to align chaos reigns but in some materials which we call ferromagnetic things like iron things that can be magnetized there is more of a tendency for those domains to stay aligned once they've been magnetized and again just an image to kind of help you visualize what's going on here so we see for an unmanned autonomous aerial we've got these different domains which are represented by the sort of different shapes these these odd shapes within the object we've got all these little atoms in there which all have their their little magnetic fields and within a domain they're all aligned but looking at the object as a whole the domains are all scrambled at this point but then as we move to the right and everything comes into alignment that's where we end up with a noticeable measurable magnetic field so then once we've got an object that's magnetized can it ever go back to being demagnetized absolutely all we have to do is scramble up those domains again we have a bunch of different ways that we can do that here are a few one is we could confuse the the magnet by throwing in another magnetic field in a different direction so if I've got like a nice happy bar magnet and then I put it in a field that's going in a different direction some of our domains will get confused as to which way they're supposed to go and will scramble things up that way we could heat up a magnet that will tend to demagnetize it as well because as the particles move faster our electrons start spinning in different directions and we with with scrambled domains and the last option of my favorite the one that I use the most often is just to beat the crud like physically out of a magnet like actually hitting the magnet will tend to scramble those domains as well some of you may have experienced that if you drop a refrigerator magnet too many times on the floor it will stop sticking to the refrigerator that's because by dropping the magnet you are scrambling those domains so stop abusing your magnets okay um so that's bar magnets let's jump over to electromagnetic fields and those current-carrying wires so just like with bar magnets the magnetic field produced by a current carrying wire will also come in the form of closed loops so we have left the the realm of straight field lines everything circles now everything is in loose okay now if we wanted to predict the direction of that magnetic field produced by a straight current carrying wire all you need is your right hand we're gonna use something called the right hand rule to predict which way that magnetic field is going and so to do that what you do is you identify the direction of the current and then place your thumb in alignment with that current so if the currents going up you have your thumb go up if the cards going to the left you have your thumb going to the left like whichever way your your currents going that's the way that your thumb is going is in alignment with that and then once you've done that your fingers can only curl one direction like they can't like maybe some of you are double-jointed and can do terrifying things but I can only really curl my fingers in one direction my fingers then represent the magnetic field and show me which way that magnetic field is is moving around the wire now what this means is that we're inherently in three dimensions when we're talking about magnetic fields and a lot of times we're trying to communicate that information on a two-dimensional medium like a piece of paper or a computer screen or something so just to kind of help us out with a little bit of notation there right left up and down you are and you know how to do that any directions within the plane of the paper are pretty straightforward then we also have another set of directions to sort of keep track of here right so you can do up down right left but then there's also the direction of coming out of your piece of paper or going straight into your piece of paper so to indicate those directions we use an X to indicate going into the paper and a dot to indicate coming out of the paper I tend to think of it as like if I imagine this is like an arrow that is following that direction like if I imagine an arrow coming out of my paper and coming towards my face I'm gonna see the tip of the arrow so it looks like a little dot if an arrow were instead moving away from me going into my piece of paper I would see the fletching the feathers on the back and therefore it would look more like an X this is where I really wish that I were there in person to talk you through all of this but um you know what that's okay we're gonna keep going and do what we can with this so let's check your understanding and see how how this is all going for you so far so imagine that you've got an electric current pointing out of your screen that you are watching this on and straight towards you so first how would you represent the direction of that current if you were to draw it on your screen so again the thing that represents coming out of the screen is going to be a dot okay dot indicates coming out of the screen towards you second question is what is the direction of the magnetic field produced by this current now to do that we're gonna need to use our right hand alright now once again your thumb represents the current so if the current is coming straight out of your screen towards you I want you to like karate chop your your screen whatever it is all right so that your thumb is now pointing straight out of your screen the same weight of the current is all right now once I do that my fingers can only really curl in this one direction which is counterclockwise and so that tells me that the magnetic field lines going around this this current carrying wire must be counterclockwise last question does this magnetic field have a North Pole now because the North Pole is a place where our magnetic field lines are all exiting out of and right now we just have a circle and if it's just a circle and this constant cycle there's no one place where the lines are constantly going out or a place where they're constantly going in so a straight current carrying wire produces a magnetic field but that magnetic field does not have a North Pole and a South Pole last big thing here so we've talked then about the the magnetic field produced by a straight current carrying wire but the wire doesn't have to say straight we can we can loop it alright and if we were to loop this this current carrying wire we can imagine then continuing to use that right hand rule to kind of see how all of the the magnetic field lines produced by this current carrying wire continue to loop around the wire all right and when we do that we end up with a shape that uh that looks kind of like this where we've got those those closed loops going all the way around or wire and this should look familiar because this looks like the field of a bar magnet then where we've got essentially this this doughnut shape to our magnetic field lines um and so this turns out to be a really useful thing for us for creating these electromagnets um is looping this wire then a bunch of times to try to strengthen that magnetic field and by by looping this wire creating a coil we end up producing a magnetic field that looks like that of a bar magnet now what we call this coil then this current carrying coil is a solenoid it gets a special name and so solenoids look something like what you see on your screen right there they produce magnetic fields that look like the magnetic field of a magnet now looking at this magnetic field where do you think then since it's like a bar magnet where do you think the North Pole and the South Pole of the solenoid are located well what I see here is that the field lines are exiting the solenoid on the right and they are entering the solenoid on the left which means that the North Pole must be on the right the field lines are leaving the solenoid and the South Pole must be on the left where the field lines are entering the solenoid last check for understanding question consider these four statements about fields which of them is going to be true for all magnetic fields including those produced by bar magnets current-carrying wires and solenoids well it can't be correct because straight current-carrying wires do not have north and south poles and seas not correct because electric fields don't form closed loops and so D can't be right because two of those are incorrect the only one that remains possible is B the field lines always form closed loops all right that is your primer on magnetic fields and electromagnetic fields good luck you've got this carpe diem you're brilliant have fun