 Hi, I'm Zor. Welcome to Unisor Education. We continue talking about nuclear reaction. In this particular case, we will talk about something which is called fusion. This lecture is part of the course called Physics for Teens, presented on Unisor.com. I do suggest you to watch this lecture from the website because, first of all, every lecture has notes, which basically, like a textbook, dedicated to this particular material in this particular lecture. All the lectures are obviously logically related to each other, and there is a menu which basically guides you how to go from one topic to another. The course contains many problems and exams, which you can take as many times as you want. The website is completely free. There are no advertisements, so everything is concentrated on your studying. So I do recommend you to use it. And then there is a prerequisite course called Math for Teens on the same website, which basically presents all the information in mathematics which is needed for physics without mathematics. It cannot be actually studied successfully. Okay, now, talking about fusion. Well, first of all, let me just briefly remind you that we did talk about nuclear reaction called fission. Fission is when we split a nucleus of, let's say, uranium-235 or plutonium-239 into pieces. Now, what happens in this case, which is extremely important, pieces into which the nucleus of, let's say, uranium-235 is split has the total mass less than initial nucleus of uranium. It's called mass defect. And the problem is that this extra mass, which seems to be disappeared, it's actually converted into energy, which is based on the famous formula of Einstein, which connects the total amount of energy concentrated in mass as mass times square of the speed of light in vacuum. So, this defect, mass defect, which seems to be like disappearing mass, is converted into energy. And that's how we're using this energy in peaceful, for instance, for nuclear power stations and not so peaceful with atomic bomb cases. Now, the fusion is in opposite reaction. So, fission is splitting a nucleus of a heavy element like uranium or plutonium. Fusion is getting two pieces together into a bigger piece. Now, there are certain cases when during this procedure operation, whatever it's called, we will have exactly the same effect, mass defect, which in theory can be used for producing energy. And the first example I would like to start with is the very simple one. You have a hydrogen, but not just just a hydrogen, an isotope which has one proton and one neutron. So, we have two different particles, neutron and proton. It's called deuterium. And then we will add another one called tritium. We have one proton plus two neutrons. It's still hydrogens because it has only one proton. So, electrically, the nucleus has electric charge of one unit. But the number of neutrons is different. In a regular hydrogen, this is regular hydrogen, one proton and that's it, no neutron. And obviously, electron around the orbit. Now, this is about 99.8% of all hydrogen which can happen in our environment. Now, this one, the deuterium, is the rest, which is like 0.02% or whatever. And this one, tritium, it does not really occur naturally. However, if we have these two atoms and they can be actually created in some physical conditions without talking about this, then there will be a very interesting reaction. It will create a nucleus of helium, alpha particle, which has two protons, these two protons, and two neutrons, which makes the total number of particles in the nucleus 4. And one extra neutron, which has no electric charge. So, basically, this is an equation, number of total particles, 2 plus 3, 5, 4 plus 1, 5. So, these are two isotopes of hydrogen and this is a nucleus of helium, alpha particle. So, this is a reaction which actually can happen. Let's talk about mass. Okay. 2.014 plus 3.016, this is 5.030. This is helium 4.0015, nucleus 1.00867, total 5.010. Okay? So, what do we see? This is difference. So, the results are lighter, if I can say lighter, has less mass than the original. So, where does this thing go? Here. This is the mass. That's how energy is released. So, great. So, why don't we do it and create energy from hydrogen? Hydrogen seems to be the most abundant element in the universe, the simplest one. Well, there are some problems. So, let's talk about problems. So, the first problem I have already described. The problem is this one, the Ethereum is very, very rare. It's kind of 0.02% of the total, but still we can do it. We can still extract the Ethereum from the water, for example. Now, it needs some energy, but it can be done. Now, this one should be created artificially, which is not easy, but probably can be done. And it also requires energy. Well, so the first question is, does this energy which can be released greater than the energy which we have to really spend to create these two? Well, it is greater, but that's not all the problems which we have. The most important problem is that this reaction requires something like 100 million degrees, let's say on the Kelvin scale. That's a lot, 100 million degrees, that's a lot. Plus pressure, sufficient to get these two nuclei close to each other. So, a huge pressure and huge temperature. So, that's the difficulty. Now, the physicists aren't working on this, don't take me wrong. Now, there are at least two different kinds of installations which are trying to create whatever is necessary conditions for this thing. Until very recently, the amount of energy which we need to produce all this, including temperature and pressure, exceeded the amount of energy which we can extract as a result of a fusion. But recently there were a couple of experiments where the net result was actually positive. But it's a good sign, but it's not really ready for production. Let's put it this way. At the same time, if we want to do something without any kind of control, that we can do because something like atomic bomb, which is based on fission of uranium or plutonium, can locally create temperature and pressure needed for this thing. And so-called H-bomb or thermonuclear bomb has been actually created. So, some bomb related to this fusion has been created and the temperature and the pressure were first created by atomic bomb based on uranium or plutonium. And that caused the reaction of these components to fuse together and release a huge amount of energy. So, this bomb is much more powerful than atomic bomb or A-bomb. So, A-bomb and H-bomb. A is atomic, which is uranium based or plutonium based, and H-bomb is based on hydrogen. Okay, but that's the bomb. I mean, we don't want to talk about bombs. We don't want to use them. We don't want to have them. We need a peaceful way of producing this energy in a controlled fashion. And that's what physicists are actually working on right now. At the same time, there are naturally occurring conditions sufficient for reaction of fusion. And these are natural conditions which exist in all the stars. Because the energy of the stars, like the energy of our sun, is based on this fusion reaction. Now, there are many different fusion reactions. Whatever I was just talking about is just one particular example. There are some others. And one of the reactions which can be observed, well, observed probably is not a good word, which happens in our sun, is slightly different, but it's still the fusion reaction. It's just a little bit different. And here it is how it's done. So, sun is burning. So, there is a temperature and there is a pressure inside. So, the first reaction which happens is just a regular hydrogen, two different nuclei of hydrogen, based on the temperature and the pressure are fused together and they create a deuterium. Now, there is a disbalance here. So, the total number of particles is correct, but we have one less electric charge, right? This is proton, this is proton and this is only one proton. So, where is exactly the other charge and how it's done? Well, apparently one of these protons converted into a neutron and positron. Positron is anti-electron. So, anti-electron, electron is negatively charged and anti-electron positron has a positive charge. So, that's where the extra charge goes. Plus some neutrino, some other weird particles which don't have any electric charge, don't have even mass. So, this is the first reaction which happens. So, now everything is in balance. This has positive charge of one plus one and here also one plus one. Now, this is very light. This is anti-electron. It doesn't have a unit mass. The unit mass is heavy particles, proton and neutron. So, we have before two and now two. So, everything is in balance. Okay. Now, that's the first reaction. Now, what happens then is this deuterium is fused again with regular hydrogen reducing helium. But not just the regular helium, the isotope of helium. Helium has two protons and two neutrons. Now, this one has only one neutron and that's why it's isotope. However, it's helium because it has two protons. Now, the next one is two helium are producing regular helium plus two atoms of regular hydrogen. Now, two plus two is four. So, we have a charge of four. Two plus one and one. So, that's four. Total number of particles, six, three and three. This is four and this is one and one. So, we have the balance. So, that's what actually happens inside the sun. And energy is released here, here and here because if you will put all the masses of all the components, we will have mass defect here. So, this is lighter than this, this is lighter than this, this is lighter than this. So, energy is released on all kinds, on all transformations. So, this is what happens in our sun. So, net result is from these two atoms of hydrogen. We have one atom of deuterium, then deuterium plus another. That's three atoms of hydrogen. Now, one, two and three produce one atom of helium. So, two of these, now it's inside this, we have three transformed nuclei of hydrogen. Now, it's two of them, so it's six. So, out of six hydrogen nucleus, we have helium and two back generated. Net result is we consume four atoms of hydrogen and produce one atom of helium. So, basically what sun does, it burns hydrogen producing neutral helium. So, that's basically the source of energy. Four atoms of hydrogen produce one atom of helium and that's basically how the sun is working. Now, there are some other reactions of fusion and fission as well, which I did not describe. Just because they don't seem to have a practical purpose, because the mass defect may be very small, or mass defect is instead of positive energy, it consumes energy, so it's negative. So, it all depends on different things. But in any case, there are other reactions which do happen, for example, inside the sun or during the explosion of A-bomb or H-bomb. So, all these reactions are kind of lesser of importance than whatever I have described, but they do happen. So, the universe is messy. I mean, whenever something like sun burns, all kinds of things, all kinds of transformations actually happen. So, these are kind of main ones and that's why I have described them. Okay, so that's how sun is working. I do suggest you to read the notes for this lecture and good luck.