RSD Academy - Inductors Part 1 - Introduction to Inductors

hi welcome to rsd academy i'm bob duhamel and today we are go oh wrong shirt there that's better today we're going to talk about inductors in previous videos we talked about capacitors which are a very simple electronic component just two conductors separated by an insulator an inductor is equally simple it's just a piece of wire that's wrapped into a coil so how can a coil of wire make a useful electronic component well let's take a look at it and see how that works to understand that we first have to understand the relationship between electricity and magnetism so let's start by just having a group of electrons i'll just draw six dots here representing some electrons that are just sitting in space and not moving and there's nothing special about them when they're not moving but if they start moving let's say they start to move in that direction doesn't matter which direction they move but when they are moving and only when they are moving they will have a magnetic field around them i'll just draw some ellipses here to represent the magnetic field that is surrounding them and as they move in this way the magnetic field let's say that this pin is moving towards you is the group of electrons the magnetic field would be a circle around the moving electrons and when they stop moving that magnetic field disappears so when electrons move and only when they move there is a magnetic field around those electrons but when they stop moving the magnetic field disappears how can that happen well it has to do with special relativity a magnetic field and an electric field are actually the same thing but viewed from different relativistic frames of reference and i have another video that explains that i have it linked up in here and down in the description below i don't want to get into that i got into that in the other video but let's just look at what happens and not why and when electrons move they have a magnetic field around them when they don't move they don't have a magnetic field now likewise let's say we have these six electrons and they are inside a magnetic field and that magnetic field is not moving and the electrons are not moving nothing special happens there's no interaction between them but let's say that magnetic field moves let's say it moves from right to left when that magnetic field moves and only when it moves the electrons will react by moving perpendicular to the direction that the magnetic field moves so this magnetic field is moving this way the electrons will move perpendicular to it it depends on the polarity of the field but let's just say that the polarity in the motion is such that these electrons now move in that direction so the magnetic field is moving this way the electrons are moving that way now it's a little more complicated than that because of the way they interact the fact that the electrons have a magnetic field around them as well when they're moving it gets kind of complicated and then they will actually move in a curve but in a wire they're confined and so it doesn't matter so we'll just assume that they move in a perfect right angle to the movement of the magnetic field but when that magnetic field stops moving the electrons stop moving and of course if the magnetic field moves in the other direction the electrons will move in the other direction so once again this all has to do with the interaction of electric fields and special relativity and i talk about that in another video but that's just what happens so once again electrons are not moving nothing special but if the electrons move they have a magnetic field around them when they stop moving the magnetic field disappears and of course when they start moving the more electrons you have moving and the faster they're moving the greater that magnetic field so as they start to move that magnetic field builds as they stop moving it collapses so we now have a moving magnetic field they start to move magnetic field builds up if they're moving at a steady rate steady number of electrons in other words a steady current that magnetic field will be steady but if they stop moving in other words the electric current drops that magnetic field will collapse so moving electrons create a magnetic field as they start to move it builds up and actually have the magnetic field getting bigger so the magnetic field is moving and as they stop that magnetic field collapses and we get the magnetic field moving in the opposite direction and once again when you have electrons in a moving magnetic field the electrons will move at a right angle to that magnetic field so that is the interaction between electrons and magnetic fields now let's take the next step and see how that leads to how an inductor works so let's just have a wire here and of course that wire is full of electrons free electrons that are free to move about as long as there's nothing to make them move they're just going to just drift in one direction to the other whichever way they want to move if one electron goes this way another one has to go back to take its place so that the electrons stay evenly distributed inside the wire and so any magnetic field from these electrons moving and drifting around is going to be canceled because if one's moving this way and the other one's moving the other way we have no magnetic field around that wire now let's put some voltage across it let's put positive to there negative to there and the lower voltage or the negative voltage is going to repel the electrons and cause them to move in the opposite direction so i put the voltage like this the electrons will move so what's going to happen of course i'm going to get a magnetic field around that wire and when i take this voltage away the electrons will stop and the magnetic field disappears okay that's something we've already established now let's do that again but let's have two wires next to each other here's wire number one there's some electrons in the wire here's wire number two and here's some electrons in the wire okay no voltages applied to the wires nothing special is happening now let's apply that voltage to this wire again positive to negative the electrons are going to be repelled and move in this direction and we're going to get that magnetic field and as that magnetic field builds it's going to pass across the other wire so we have a moving magnetic field moving past the other wire as that magnetic field gets bigger so what's that going to do well the moving magnetic field is moving in that direction so it's going to make the electrons move perpendicular to the motion of the fields the field is going that way the electrons are going to go one way or the other it depends on the polarity of the magnetic field but if these electrons are moving this way the building magnetic field crossing the next wire is going to cause the electrons in that wire to move in the opposite direction so we have a phenomenon here that's called mutual induction the movement of the electrons in this wire causes the magnetic field to build which induces a current in the other wire mutual induction and that current goes in the opposite direction so we have one wire affecting another wire due to the magnetic coupling between the wires this becomes important in alternating current in a device called a transformer where we use that magnetic coupling to do some useful things but we'll talk about that in the future when we get into alternating current so this is dc the electrons begin to move as they begin to move we get the magnetic field as that magnetic field moves across the other wire the electrons in that wire move the opposite direction but of course eventually this current becomes a steady current and when we have a steady current the magnetic field is a steady magnetic field and is no longer moving and so once that magnetic field stabilizes and stops moving the electrons in the other wire stop moving so we still have the current in this wire but we no longer have a current in this wire because the magnetic field is no longer moving but of course what happens if we reduce the voltage that current is going to reduce and that magnetic field is going to collapse and move the opposite direction so what's going to happen if the building magnetic field caused these electrons to go that direction well the collapsing magnetic field is going to make them go the opposite direction so as that magnetic field collapses that's going to make these electrons move the same direction as the other wire so as the magnetic field builds we get current in the other wire that goes this way once the magnetic field stops building and stays stable the current stops in the other wire but if we reduce that magnetic field as it collapses it makes the electrons move the opposite direction so that's one step closer to understanding how an inductor works so now let's make these two adjacent wires two turns of the same coil of wire let's go ahead and redraw that try to draw this in such a way that it makes some sense let's just draw this wire here and this wire here again and there are two turns of the same coil so let's draw i'll just do some dashed lines here and i'll round that off on the end to show that that is the end there's that one let's just round them all off and so here's the wire and of course we have some another wire coming in that way and this is going off in that direction so these are the turns closest to us and the turns furthest for from us are the dashed lines so we have the coil coming it's coiled up in that direction and so here comes the wire and it's coiled and these are the close coils those are the far coils and it's coiling that direction i'm just showing two turns of the same coil of wire i hope you can see what i'm doing here so now if i push current into that wire there goes the current into the wire it's going to go that direction go up to the next turn and then go that direction and up the next turn and so on all through the turns in the coil of wire so i have the current going this direction and the current going this direction and in the back it's going of course spiraling around along with the wire now how do these two turns of the same coil interact with each other well let's start to put the current in that's what's going to happen let's just look at this turn first we push the current in we get a current going through the turn of the wire magnetic field is going to build and it's going to cross the other wire but it also has a current going in it in the same direction so what's going to happen well remember that the building magnetic field is going to try to make a current that goes in the opposite direction so current in this wire or current in this turn makes a magnetic field that builds up crosses the next turn and tries to make a current go in the opposite direction but it's opposing the current that's in there which is doing exactly the same thing so this turn has current in it has a building magnetic field that crosses the other one and that tries to make a current that goes the opposite direction in this one so we have these currents that are creating a magnetic field that's creating another current that goes in the opposite direction what's what's going on there well of course what happens is this magnetic field builds up it tries to induce a current and here that pushes the opposite direction so we have one current going this way another current opposing it so what happens basically nothing so let's back away from this let's just draw a coil of wire out in free space so here we have a wire we coil it up and we've just established that if i try to push a current into this coil we can go ahead and use conventional current now it doesn't really matter don't need to follow the electrons anymore i try to push a current into this wire i'm going to get all these little magnetic fields building up crossing the other turns which are going to create a current that tries to push the opposite direction so what happens i try to push current into this coil it creates a current that pushes the opposite direction and says oh no you're not either so when i try to push a current into a coil of wire the coil of wire pushes back this is exactly the opposite of what a capacitor does remember a capacitor when i push a current into a capacitor the electric current comes in if this is if we're following the electrons a bunch of electrons come in they push electrons off the other side so we see current go in we see current come out looks for all the world like the current went right through it so when we push current into a capacitor it looks like a short circuit for a moment but the inductor looks exactly the opposite we try to push a current into it it looks like an open circuit it says oh no you're not either but then what happens let's get the capacitor out of here for a moment so here's our coil of wire again we try to push a current in the coil of wire because of the building magnetic field causes a voltage to build that tries to push a current the other direction it says no you're not either so it looks like an open circuit but what happens eventually that current is going to build up that magnetic field is going to stop building so now after a while we have here's a drawing of the magnetic field around that coil there's a current going in it's going right through and coming out why is it going through because now this magnetic field is no longer moving if the magnetic field is not moving it has no effect on the currents in the wire it's not generating currents it's not pushing back or anything so after a while the coil looks like exactly what it is just some wire as long as that magnetic field is not moving it's not affecting the current and the current goes through it just like it's a piece of wire which is what it is which is just the opposite of the capacitor remember what happens to the capacitor eventually we get these electrons going in they push electrons off it looks like a short circuit because current goes in current comes out looks like the current goes right through but after a while these electrons build up and there's no more electrons over here the current stops and the capacitor looks like what it is an open circuit the inductor did exactly the opposite after a while that magnetic field finally stopped moving and we have a steady current steady magnetic field no interaction and the current goes through the inductor just like it's a piece of wire which is what it is now what happens if i stop the current well if i try to stop the current that magnetic field is going to collapse and so remember what happens when we had the two adjacent wires when the magnetic field built up it pushed the current one way when the magnetic field collapsed it pushed the current the opposite way and exactly the same thing is going to happen here so originally we tried to put the current in as the magnetic field was building the inductor pushed back but once the magnetic field stopped moving current goes through it like it's a piece of wire now we try to stop the current that magnetic field is going to collapse what's it going to do it's going to induce a new current that goes in the same direction so now i try to stop the current and the inductor says oh no no you've got to keep on going i'm going to keep feeding energy into you and keep that energy going so the inductor has an action sort of like a flywheel if you can think of like a potter's flywheel which is made of a large circle of concrete has a post that goes up to the little potter's wheel where he can do his pottery and if it's not electric they will start it with their feet which is kind of a good way to illustrate how a flywheel works because that big heavy flywheel at first is going to be hard to get going it has a lot of momentum and you have to push kind of hard to get it going but once it's going it's easy to keep going because it has momentum and it wants to keep going now it's hard to stop so it's hard to get going but once it's going it wants to keep going same kind of thing happens with an inductor it's hard to get current to go through it but once we get the current going through it wants to keep going through it it's hard to stop so an inductor has an action that's sort of like a flywheel so this was discovered by joseph henry actually joseph henry and michael faraday were doing some of the same experiments and they credit the discovery of what this is which is called self-induction to joseph henry so basically what he was doing he was working with an electromagnet which is a coil of wire and of course what happens let's put a battery on here and a switch and we close the switch we get a current through there magnetic field builds up and we have a magnet and you can pick up little bits of metal with it and open the switch and the magnetic field disappears and the magnet drops everything what joseph henry discovered though was that when he opened the switch he got a little spark across there and he speculated what could have caused that at first he thought well in those days they called electricity electrical fluid they knew it was some kind of a fluid flowing through the wires and he said aha this fluid has momentum and when i open that switch it wants to keep on going and is able to jump that and make a little spark but he realized later that what was happening is when he opened this up that magnetic field rapidly collapsed and actually you get more voltage across there than well you can get more voltage than you put in let's say this is a 10 volt battery and he closes the switch and what we're going to get of course is this is a standard dc circuit you know battery inductor 10 volts how much voltage are we going to get across the inductor all of it it's just like a resistor we have one resistor we get all of our voltage across that one resistor so we have all of our voltage across the inductor i said it's just a piece of wire well of course it has some resistance so we have 10 volts how many ohms maybe you know one ohm or whatever but we're still going to get all of that 10 volts across here and the resistance is going to determine the current through the inductor so if we have 1 ohm worth of wire and 10 volts we're going to get 10 volts across there and of course 10 amps but when we open that switch and that magnetic field collapses it can collapse so quickly that it induces more current or more voltage than you originally put in and so that could be enough voltage now as put across our switch so where's that voltage going to go it's going to end up across the the switch the open switch here and is that enough to generate a spark oh yeah it depends on just how close the switch contacts are and so you get a little spark because it i it's enough voltage to ionize the air and cause a spark and so henry realized it was the collapsing magnetic field that caused the voltage across there that generated the spark and we call that self-induction now we'll talk about how inductors work in alternating current when we talk about alternating current down the road but in direct current how inductors are useful is their property to keep a current going at a steady rate remember we try to push current in it says no you're not either but once we get the current flowing it wants to keep the current flowing at that rate so an inductor resists changes in current does that sound like it could be useful yeah in different ways uh for exa so so an inductor resists changes in current does that sound like it could be useful in dc circuits you betcha for example let's say we have a voltage that's kind of fluctuating over here and we don't want those fluctuations to get over here we just want a steady voltage well what's going to happen as this voltage tries to go up the inductor is going to push back as the voltage tries to go down the inductor is going to push forward and that's going to mitigate these changes and reduce the amount of fluctuations on the other side when we talk about alternating current and especially in analog circuits when we talk about converting ac to dc this becomes very important and when we have alternating current that we have to convert to dc well an inductor can be very useful to filter out any residual alternating current which is left over in one circuit from getting to the other also in radio circuits where we have once again alternating current of very high frequencies and then we have some other circuit over here we don't want these fluctuations to get over to the other circuit yeah put a coil in between in those cases it's called a choke coil so if we're using it in dc circuits to filter out fluctuations over here uh we call it a filter but if we're trying to keep a radio frequency from getting from one place to another we call it a choke why do we call it a different name well it's just the way we name things it just depends on what the job is so we might hear of choke coils or filter coils in either case they're trying to get fluctuations in one circuit from getting over to another so very common use of inductors now in alternating current we can use inductors to make tuned circuits to make filters to make oscillators but that's for down the road when we talk about alternating current so there we have it the basics of an inductor it acts like a flywheel we try to push current in it tries to push back but once the current is flowing it lets it flow freely and then it tries to keep the current flowing it's hard to stop hard to start current flowing through an inductor hard to stop it once it starts and that's the basics of what they do at least in dc circuits if you found this video useful and informative please give me a thumbs up down below it's very helpful to the channel any questions put them in the comments i answer as many questions as i can and when i can't answer them sometimes other people do if you want to know when i'm putting videos online be sure to subscribe and hit that grey bell button better yet go to rsdacademy.net and enroll as a student it's free and when you do you're on my mailing list i don't send out too many emails but i do tell you when i put up new videos and other useful information about rsd academy and remember rsd academy is a free online vocational school where you can study electronics technology and you can prepare for a career as a certified electronics technician and to help put these videos online and keep vocational education free at rsd academy you can pledge your support at patreon by going to patreon.com join rsd academy and pledge your support and a big thank you to my patrons at patreon your donations of as little as a dollar a month make a big difference and help me put these videos online and help keep education free at rsd academy and a big thank you to everyone for watching

Channel: RSD Academy

Views: 4,475

Rating: 5 out of 5

Keywords: Basic electronics, electronics school, free online classes, electronics classes, learn electronics, learn electronics technology

Id: ucHlUzLKWlg

Length: 24min 6sec (1446 seconds)

Published: Sat Jun 13 2020