 Hi, I'm Zor. Welcome to Unizor Education. Today we will continue talking about electronics, which means usage of electricity for other purposes than mechanical rotation or heat. Well, primarily electronics are used in radio, television, telephones, etc. Now, the previous lecture was about one particular device called diodes and how it's arranged, how it works, its main principles, and today we will continue talking about another device called triode. So triodes are kind of slightly different than diodes and they have a slightly different purpose, but it's a relatively simple electronic device, which is used everywhere. I mean, wherever you go and you have electricity, you will have triodes and diodes and resistors and some other things. Anyway, so triodes are just one of the most elementary electronic devices and that's what we were talking about today. This lecture is part of the course called Physics for Teens, presented at Unizor.com. On the same site you can find the prerequisite course, Maths for Teens. Now, the site is completely free. There are no ads, so you can use it at your purpose at any time and for those who are interested in challenging themselves, the course has a lot of exercises and exams. You can take it as many times as you want and you will be basically graded. Okay, so triodes. The main purpose of this device called triode is to amplify signals. Well, and amplification is definitely needed for radio, for instance, when a very weak signal actually is caught by antenna and you want to basically amplify it. So, we will talk about how this particular device is made, arranged, what's the principle of its work and I will use the old-fashioned vacuum tube construction just to demonstrate the principle. Contemporary triodes and diodes and everything else actually is produced differently. They're using semiconductor integrated schemas, etc. But in any case, the most important is the principle and that's the purpose of the whole course actually. I don't go to any real technical details, but the principle is important and the principle is very well demonstrated when we examine the very first triodes made by certain inventors and they are based on vacuum tubes. Okay, so let's start with whatever we had the previous lecture, the diodes. If you remember diodes have the heated cathode which has certain electronic cloud because it's heated and electrons are they're making very, very fast movements because of the heat exaltate them. What's the word and we're looking for the word? Excites them, okay, and they have, they form the cloud, electron, electrons cloud around this. It's called termionic emission. So the termionic emission the heated cathode has this electronic, electrons cloud. So this is a minus for instance, okay. Now, this is a plus and this is anode. So now if this is minus and this is plus, the electrons in this cloud are attracted by positive anode and they flow and there is an electric current, but if this is plus and this is minus there are no excess of electrons here. So there is no cloud. So the current is not really going. The electrons actually are not going from minus to plus. Anode is cold. So electrons do not have any kind of, there is no termionic emission on there because anode is cold, cathode is hot. So it's always electrons are always going from hot to cold, okay. So that's why if you have an alternating current here, then when this is minus and this is plus, electrons move this way. When this is minus and this is plus, electrons do not move. So that's why we have the graph of flow of electricity like this. Instead of if we do not have this, if we will have a direct connection, this is the variable alternating current going back and forth, back and forth, but in case if we have this construction, we have basically cut that piece and we had some other smart devices to make the smoother that was in the last lecture. But I wanted to remind you the construction of the diodes because this is the first step in creating a triode. Now, what happens if we will put a grid negatively charged here? Well, when cathode is negative, you have this termionic emission, you have cloud of electrons, but if this is negative, it actually repels all these electrons and electrons could not really go that way. So my point is that while it's still working as a diode, so to speak, I mean only if it's negative and this is positive, we can really think about electric current, not when this is positive and this is negative. However, even in this case the flow of electrons can be controlled by the voltage between this and this. So between these two, between cathode and the grid. If there is a negative voltage here, then this flow of electrons will be, well, smaller basically if you wish. So this is the main principle. By changing the voltage negative voltage, relative to cathode on the grid, we can prevent, partially or completely, the flow of electrons. Now, why do we need it? We need it for this purpose. This will be the voltage between these two, will be our input voltage, so to speak. And the voltage which we can get from between cathode and anode would be our output voltage, so to speak. I'll talk about a concrete schema a little bit later. But this is the purpose. So by changing the potential between anode and cathode, we can change the intensity of the flow. But changing the voltage between grid and cathode, we can regulate this flow. And that's the main kind of idea behind the amplifier, which allows to even smaller input voltage between grid and cathode, convert into synchronous, but by amplitude higher amperage between cathode and anode. Okay. So that's the principle. What I would like actually to do right now is to present a concrete schema, very imperfect. However, it demonstrates actually the principle of amplifying the signal. Okay. So it's done the following way. So let's assume that we have some kind of vacuum tube here. Okay. I forgot to mention one little detail. Sometimes the cathode is arranged a little bit more, I would say, more sophisticated if you wish. You see, we have to heat it, right? Because the cathode is supposed to be heated to form the thermionic cloud. Now, if we will just connect it to the source of electricity, so it will basically heat by electricity, by direct current, let's say. It will interfere with these voltages between cathode and anode. So what's actually done, we have a parallel kind of a spiral here. And here we have heated element. So this is heated, but this is very close to it, so it actually heated as well. But without interference of voltage or current from this battery, which is supposed to just just just to heat the cathode. Alright, so but this is a small detail. The main principle is, so you have this cathode and this anode and cathode is heated. Now, let's consider that we have an input voltage between these two. Whatever the variable signal is. It can be a radio signal, for instance, which somehow, using antenna, is converted into small oscillations of the voltage between these two, between the grid and the cathode. So this is my input. Voltage. Now, on the other hand, we will have this thing connected. But we do need a source of energy. Let's say we have a DC battery here. Relatively powerful. So we have some kind of a difference of potential between cathode and anode and this might be more powerful, actually. Now this is input. Okay. And now what I will do between this Well, I do need some kind of a load here, so we don't have a shortage. Okay, let's say this is some kind of a load. So we don't have a short but we also would like to have an output voltage. And output voltage is between cathode and anode. So this is my output. Now what happens is the following. For instance, grid is neutral, relatively to cathode. So there is no changing voltage or anything like this. There is zero here. Well, then what happens is we do have heated cathode and anode will be positively charged, cathode will be negatively charged. So the flow will be just one way like a diode, right? Okay. Now the intensity of this flow depends on the power of this source of electricity, this DC battery, right? Stronger the battery, the more voltage it creates between anode and cathode, the more intense the flow of electrons will be and that's why we have a higher amperage. So amperage depends on this. Now and it can be relatively high, obviously. Now what happens if using this negative potential on my grid, I will regulate this. Well, if I will put some negative charge relative to cathode on this grid, it will prevent electrons. So if this is my input voltage, so it's changing, let's say the radio signal it has certain frequencies, amplitude, etc. So as this thing is changing, so the flow of electrons, however powerful it is, depending on the power of this battery, will also fluctuate. It will fluctuate in sync with fluctuation of this, but amplitude will be different because amplitude depends on this. So the flow will be different and that and therefore the output voltage between these two will also depend on the input voltage, but the strengths, the amplitude would depend on the strengths of this battery. And obviously I have to really put some some kind of ground here. So the whole thing is supposed to be grounded. That's the main principle of a very very simple amplifier. Well, obviously the real amplifiers are much more much more complex and they need some calculations. I mean what kind of voltage should be put here? And what kind of voltage is exist here to have a signal on the output, which basically is sufficient enough to let's say drive the speakers. So whenever the signal comes from the radio, let's say you have to amplify it and amplification will probably involve something similar to this one and as a result of this amplification the output will be in sync with this. So you will see the voice in exactly the same way as your transmission comes in. But amplitude will be higher, which means you will hear something because otherwise the signal is very very weak, whatever you're getting from antennae. It's a very weak signal. It can't really drive the speaker. The speaker is supposed to have certain additional power and that's what additional power is. It actually gives the strength to this signal while being completely in sync because as this thing is changing the flow of electrons is obviously changing as well. So that's why we have the same synchronousness between input and output. But the output is stronger because this battery can be strong. Well, basically that's it. Again, this is a kind of idea based on vacuum tubes, etc. This is how the first triodes, the first amplifiers were actually made. And I'm well, I don't know if I can say it lucky enough or not because I remember working with computers of the first generation, which were made with vacuum tubes. Then little later the semiconductor came. And obviously all these diodes and triodes, they have their equivalent in semiconductors, which I will describe maybe a little later when we will talk about semiconductors. But again, it's different implementation of the same idea. So basically that's the the only thing which I wanted to talk about today. This is just an introduction into a very, very simple electronic schema. So you have just some basic understanding of how all these smart devices, including televisions, computers, whatever else, are arranged inside. Okay, that's it for today. Thank you very much. I do suggest you to read notes for this lecture on theunizor.com. And they have some better pictures than this one, I hope. And good luck. Thank you.