 Hi, I'm Zor. Welcome to Inizor Education. I'm continuing talking about usages of electricity. The previous lecture was about electrical devices. Electrical in terms of producing some mechanical work or heat and optionally light if the light is related to heat, like in condensant lamps. Now, I would like to talk about other kind of usage not related to mechanical work or heat. And this is called electronics. So, electric and electronics, well, at least in my understanding, electric means related to mechanical motion and heat. Electronic is everything else. All other usages of electricity. Now, there are many different devices where electricity is used, not as the source of mechanical energy or heat. For example, television, radio, phones, internet. I mean, there are tons of different devices and I'm not going to talk about how they are built, created, designed, etc. However, all of them have certain elementary devices which perform certain elementary functions. And there are not too many of those. So, what I will do, I will cover a couple of small elementary devices from which all these radios and televisions, etc., are created. Now, obviously, these devices, elementary devices, as I'm calling them, they have gone through transformation, obviously, throughout the years. So, I will start from the invention because basically looking at the first versions of these devices gives you the understanding of how the whole principle of this thing is implemented. And then we will go to semiconductors and some future lectures. So, right now, we will talk about first devices, first elementary devices as they were invented, basically. And they are all related to vacuum tubes. So, I'm old enough, actually, to work with computers built with vacuum tubes. So, that was a very, very long time ago. But I was actually working with these computers. So, that's quite an interesting historical perspective. Okay, so, today we will consider device which is called diode, electronics, diodes. So, what is the purpose of this? The purpose of diodes, and diode I would consider to be the simplest device. So, I'm talking about the first diodes as they were invented, not about something like LED, like light imaging diodes. That's a different story. I'm talking about the first diodes as they were invented. It was somewhere at the end of 19th century, and people like Fleming and Edison were actually experimenting, and many others, obviously. So, there were certain transformations of the devices. But the principle which I will talk about today was the same for many of those. They're just improving, but idea is the same principle. So, what is the purpose of diodes? The purpose of diodes is to let the current to go only into one direction. Now, as you remember, most of our electricity which we are using is alternating current, because it's produced by powerful electric plants, like hydroelectric stations. So, we do have an alternating current. Now, in some, well, in many cases, we need a direct current. For instance, something like the phone, for instance, it's working off the battery. Battery produces direct current. Well, this is already produced, but if the input current is alternating, we, in many cases, have to change it to direct current. So, the purpose of diodes is to let the current only into one direction. So, recall that if you have source of alternating current and you have certain load here, then the reserve function u of t, which is voltage on the contacts of this generator, is basically something like sine of time, and graphically u of t is this, that's sine. Now, obviously, if you want the current which goes through here, through the load, it will be basically u of t divided by r, that's the Ohm's law, which means it's exactly the same thing. The graph would be also this, this would be I of t. So, it goes to one direction and then another direction. So, the electrons are going this way and then this way. Half of the period is this, half of the period is that. So, electrons are moving in two different directions. And, again, as I was saying, sometimes we need this to be such a thing which has only electrons going into one direction. Well, again, don't remember that the real current as we are kind of customarily saying it goes into some direction. It's from plus to minus, which means it's opposite to electrons, which I don't like, but that's the history, nothing we can do about it. So, if electrons are going this way, it means that the current goes this way. This is some kind of a historical consideration. When people didn't know about electrons, it doesn't matter. So, if we will talk about electrons, we can always say that, okay, if electrons goes this way, then the current goes opposite direction. But in any case, in this particular case, when there is nothing here, we have the voltage going plus and minus, plus and minus alternating. And that's why the current through this goes this way and this way, this way and this way. And if it's something like 50 hertz or 60 hertz frequency, it means that the 50 or 60 times a second the direction is changing. So, positive, negative, positive, negative. Positive plus negative is one period and you have 50 or 60 periods of this during the second. Okay, now we're talking about diodes, this little device, which is letting the current only into one direction. It's called rectifying, making it straight, if you wish, in unit direction or rectifying. So, the purpose of diode is to rectify the current. Now, let's talk about the invention itself, how it was done. Okay, so, first there was some kind of an observation. If you have some kind of a source of negative electricity, potential and positive, so you have some, let's say it's a battery and there is nothing in between. Well, we do have some electric potential on the contacts between this and this, so you can measure it with voltmeter, but there is no current because there is no connection here. Electrons are kind of separating, this thing is separating electrons into one direction. So, you have excess of electrons here, deficiency of electrons here, and it sits this way. Nothing happens. But let's consider that the distance between these things is not really very high. That's number one. Number two, we will put them into a vacuum tube. And number three, we will apply heat to negative contact. Now, what heat actually does, heat is increasing the intensity of atomic motions and electron motion inside the body of this electron. So, electrons are starting actually moving faster, whatever, they're agitated. Now, you remember that the top layer of the atom, top layer of electrons, is not as stable as electrons inside. And if you're talking about metals, there are many free electrons. They're basically jumping from one atom to another. It's some kind of a biological movement of these electrons. So, the total amount of electrons is still the same, but they're moving. Now, if we are heating, they're moving faster. They're moving so fast that sometimes they're jumping out from this negatively charged electrode. So, there is some kind of a cloud of electrons around this thing. And if there is a vacuum and not far you have the deficiency of electrons, which attracts electrons, these electrons will be attracted and go here. So, electrons will go here, compensating the deficiency of electrons. And that's why we have now some room available here and new electrons which batteries producing are coming here. They're also jumping because they're heated, they're jumping out. They're attracted by positive contact. And that's we have the current in this direction. Now, what if we will start heating positive instead of negative? Well, nothing would happen because there is no excess of electrons here. So, they will not jump. Even if they will jump, the negative will repel them anyway. So, there is no way anything can happen. Now, what if I will change the polarity? So, if this is the source of alternating current, then we have 50 or 60 times a second polarity is changing. So, whenever there is a minus plus, when there is a minus plus here, the current will go. If next half a period I will have plus minus, the current will not go. The electrons will not jump. There is no current in this case. So, basically, this is the main principle. So, whenever I have negative contact, and it's called, by the way, cathode, and this is anode. So, whenever my cathode, which is the heated pot, is negative, the current exists. And whenever we change the polarity, there is no current. So, let's talk about these graphs. By the way, I didn't mention this. So, this formation of cloud of electrons, it's called termionic emission. Termionic emission. But emission is kind of a normal word. Everybody knows this. And termionic means basically caused by heat. By heat. Termionic emission. So, this concept, this existence of termionic emission is at the heart of the whole device. Now, let's talk about graphs. Okay, so, this thing is producing alternating voltage here. So, my graph is the same. Now, this is plus, obviously, this is minus. So, this is the difference between potential on the contacts of this or this. Now, if this is minus, this is minus, then the current will go. Now, when I'm talking current, I'm talking about the flow of electrons. Again, not the flow of current. Current goes opposite direction by some kind of agreement between people. So, electrons are going this way. So, in this case, well, let's talk about this particular thing. This is plus. So, in this particular case, we do have the current and it will go the same way as this half a period. Then, it's a little less than that, then whenever the voltage is changing, whenever here plus and here minus, there is no current. So, my graph will be flat here. Then, again, the current, well, the flow of electrons will go when we have this particular voltage on the contact of the alternating current generator. And then, when the voltage will be on the negative side, we will again have a flat thing in the game, in the game. Now, is this a direct current? Well, not exactly. I mean, it's direct, but it's not as even as if I have a battery. With a battery, my graph will be straight line, right? Well, while battery is maintaining its charge, right? So, this is not exactly a straight line. So, my problem right now is, although I did achieve one goal, my electrons are going only into one direction and they don't go backwards. So, everything is on the positive side. However, it's not really even. So, I have this problem. Plus, don't forget another thing, that during this period when there is no current, my electric generator which generates alternating current basically works, but I'm wasting my energy. So, whenever during these periods my energy is completely wasted, whatever the source of energy is, whether it's a gas or hydroelectric station or whatever it is, half of the power is lost. So, that's not good. So, we have to work on this. We have to improve this, not very pleasantly looking, although direct current into something a little bit better. So, how can we achieve that? Okay. So, let me first introduce the symbolic. On the electronic schemas, this is the symbol for a diode. So, this thing is anode. This thing is cathode. So, this is the heated part. So, electrons are going this direction, and the current going this direction. So, you can actually consider this as an arrow which points to the direction of the current agreed upon by people. But electrons are going from cathode to anode, right? So, this is the symbol. Sometimes they use this symbol, and sometimes it's completely black, whatever it is, doesn't really matter. But the shape is the same, triangle and the straight line. The triangle side is anode, and the straight line is cathode. Now, so right now I will talk about an interesting idea which allows to use both sides of the curve, positive and negative, and convert everything into the one-directional current. It's really a very cute, I would say, solution to a problem. I mean, aesthetically it's pleasing. At least that's my personal opinion. So, people are thinking and purely logically they have designed a particular kind of schema which allows to use both sides of the cycle, positive and negative sides of the cycle of alternating current. It's called the bridge. So, it's using exactly the same idea. The diodes. They're using four diodes to achieve this goal. Here's how it's done. They have arranged a square, and they put diodes like this. So, these are four diodes. Now, this is the source of alternating current. This would be my load, whatever the load is. It doesn't matter. So, let me put the points here. a, b, c, d, e, f, m. Now, again, this is the source of sinusoidal voltage. So, let's think about it. Well, sinusoidal means either this is plus and this is minus, or this is minus and this is plus. So, let's consider a situation when a is on a plus and e is on a minus. What happens in this case? Well, b is on the minus. It means that electrons are in axis at the point b. So, this axis of electrons, I'm talking about the flow of electrons, not the flow of the current. Current will go opposite. So, axis of electrons is b. It goes to e. Now, we have left and right. Electrons are going into the cathode. The cathode must be negative to have the flow, right? So, the flow of electrons will not go here to anode. It will go to here, because this is the cathode. And eventually they go through to the point f. So, after b, we will go to e and to f. So, from f, again, electrons cannot go here, because this is anode. It goes to load, to n. n to m, obviously. m to d. Now, from d, well, let's think about it. From d they can go both ways, actually, because both are cathode. But a is positive and b is negative. So, electrons will not go to the negative. It's already axis of electrons here. So, it will go to positive a. So, from d they will go to c and a. Now, what's important is electrons are going from n to m on this load. And that's what we are actually interested in. Now, let's talk about another case. Let's say we have a is negative and b is positive. Next half a cycle. Okay, a is negative, so electrons are in axis at point a, and they go to c. So, from c they should go to f, because this is the cathode, and this is anode. Electrons don't go to anode. They don't go anywhere, right? So, they go to cathode because the cathode is heated, and that's where the thermionic emission happens, the cloud of electrons. So, they go to f from a to c to f. Okay, from f again. This is, they cannot go electrons here. So, they go to load and m, obviously, and g. Now, from d, how they go from d? Okay, from d we have both ways, obviously, again. But, now a is negative, so electrons will not go to a, because it's already axis, so they will go to e and b. Where there is a deficiency of electrons. So, this is the way. So, this is a plus b minus, and this is a minus b plus. This is the flow of electrons. Again, what's important is that in both ways, our direction of electrons is from n to m, or the current is from m to n in both cases. Which means that both sides of the cycle, when we are in this case, we are producing the current, this, and when we are in this side, we also have the same. So, the resulting is not, remember it was before, it was like this, right? Now, it's like this, which is better. I mean, it's actually twice as good. So, we're not wasting half of the cycle. We still are not exactly on an even direct current, but it's still direct current. It's an improvement, okay? Now, can it be improved further? Yes, and here is how. Let's consider you have this particular graph. This is sin of x, and this is absolute value, right? So, instead of going from positive to negative, I'm only going to positive, that's why absolute value. This is the sin of x. This is the sin of x, absolute value. Okay, here is another one. What if I will introduce a phase shift, which is sin of x plus pi over 2? So, instead of having 0 here, I will have something like this. And this goes to, top goes to 0 here, and 0 here goes to top, okay? Now, what if I will add them together? These two functions. Well, what I will have is something like this. So, it doesn't go to 0 because at the point this is 0, this is a maximum, so I will be on the top. So, if you will do the graph of the function sin of x, absolute value plus sin of x plus pi over 2, which is shifted by pi over 2, you will have this. So, this is not exactly, again, it's not straight line, but it's significantly smaller oscillation around something, and that's around something, it's not 0, obviously. So, this would go to 0, and this would go to 0, but the sum will never go to 0. So, that's very important. So, we are improving our signal by shifting the phase. How can we shift the phase? Well, if you will put something like a capacitor. Remember, capacitor is something which is shifting the phase of alternating current. And now, if you remember, go back to that lecture and think why it happens. But in any case, there are certain ways, like using the capacitor, which we have already considered before, to shift the phase. So, if you will have half of the current going into one phase and the current going to another phase, then we can actually have here on another load, we have a sum of these things. So, that's very important and these are ways to improve our rectifying. And whenever, for instance, you want to charge your phone, you put some special plug into regular AC outlet, alternating current, but on the output, which goes to your phone, mobile phone, I'm talking about, you have a direct current. Now, how they have achieved it? Well, they have some devices which, well, may be more complicated than this. But in theory, this is the main principle how you can improve your rectification using diodes. And the last thing which I wanted to say is that these vacuum tube-based diodes are very, very rarely used right now because everything is basically replaced by semiconductors which are working, I should say, on the same principle, but it's different actually. It's a different principle but the same idea to let the electrons to go into one direction and have some kind of arrangement how it can happen. Now, I was talking about semiconductors when we were talking about solar power generation using solar power. So these solar panels have these semiconductors and I was talking about how they are arranged, et cetera, but I will have a special chapter in this course which is dedicated to semiconductors. They have generally replaced the vacuum tube-based. However, I think it's very important to understand what's the source of ideas because ideas are much more important for this particular course than the regular implementation. There are some technical professions which need the detailed knowledge about how it's implemented. I'm interested in giving you the idea how the whole thing was actually invented, the beginning, because that's where the power of new ideas actually is coming from. Well, that's it for today. I suggest you to go to Unisor.com. That's where the lecture actually is and there is a textual explanation, basically the same thing as I'm talking about. It's written with much nicer pictures than this one. And, by the way, the Unisor.com contains a prerequisite course called Mass for Teens. And I think it's a mandatory director to use mass in real physics, which we are talking about. That's it for today. Thank you very much and good luck.