 Hi, I'm Zor. Welcome to Unisor Education. I would like to continue talking about nuclear power. In particular we'll talk about reaction, which is called fusion. Now this lecture is part of the course called Physics for Teens. It's presented on Unisor.com. I do suggest you to watch this lecture from the website by going through the menu, because it's part of the course. And the course has certain logical segments, it has interdependency, etc. Plus there is a prerequisite course called Math for Teens on the same website. All courses are free, no ads, no strings attached. Alright, so let's go for the fusion. Well, first of all, what is a nuclear reaction, which we call fusion? Well, the first reaction which we were talking about was fission. That's when we are splitting a heavy nucleus into parts. And during this reaction, the energy was released. And we were using a very simple analogy. If you have a spring, but you squeeze it and put some kind of thread on both ends. So it doesn't really go back to a neutral state. Now this spring has a potential energy. And the thread which keeps it in a squeezed position is restricting basically to release this energy. Now what is the analogy with nuclear? This thread is an analogy of a strong force which keeps protons and neutrons together in a nucleus. And the spring, the potential energy is a potential energy of protons which are very near each other and they are repulsing each other because they are all positively charged. So there is an electric charge and they are repulsing each other but they cannot really move outside of the boundaries of the nucleus because the strong forces keep them together. But if we somehow cut the strong forces by, let's say, bombarding the nucleus of uranium-235 with the neutron then that heat is sufficient to disbalance the system and the nucleus is split. And because of the energy, the potential energy between the protons electrostatically repulsing each other, repelling each other, is greater than the energy needed to break the strong force the total result of this nuclear reaction is releasing excess energy. Now, I will use exactly the same kind of a logic but the situation is slightly different on the lighter side of the periodic table of Mendeley. Let's say, when we are talking about hydrogen. Now, in case of hydrogen, the nucleus is very light and there is not enough potential energy in the nucleus to basically in the light elements. Actually, light means from the beginning of the periodic table from hydrogen up to ferrum to iron. So, all these nucleuses are not big enough. So, the electrostatic repulsion between the protons is not sufficient to basically overcome the strong forces if we will start, you know, bombarding with whatever we can, like a couple of neutrons hit the nucleus. So, in case of a bigger nucleus like uranium, the number of protons is very large and so they are repulsing in a much stronger way. So, there is more energy if we will separate them. So, the same kind of a fission reaction, the splitting, would not work for light elements. But precisely because of that, the opposite reaction would release the energy. So, the opposite reaction when we are not splitting the nucleus but the other way around, we are taking two lighter nucleus, nuclei and combine them together into a little bit heavier one. That reaction will release energy because in this particular case, the difference between strong forces and electrostatic forces are working in the opposite direction. So, let me just explain it on a particular example, like analogy, which I am using analogy with the spring and the thread here and I will use some other analogy for the opposite reaction for the fusion. So, again, what happens if we are bringing close together the two light nuclei? Well, we have to go against electrostatic repulsion, right? Because we have protons here and protons there, so they repel each other. So, we have to do it. However, if we will move them sufficiently close, then the strong forces, which are working on a short distance but they are very strong, will actually overcome the repulsion of the electrostatic forces and they will bring together a heavier nucleus. And the difference between the energy which is spent to bring them together and energy released by the fact that potential energy of the strong forces will be actually spent, will be released when they are combined together into one nucleus. So, the strong forces, this potential energy in the strong forces is greater and the release of energy whenever they are falling on each other is greater than consumption of energy to bring them together. Now, and here is the example which I kind of came up with to explain this situation in a, well, more or less similar way. In this case, we will use two magnets. Now, this is north, this is south, this is south, this is north, and there is a spring in between in the neutral position. Now, what kind of forces are actually working here? Now, I am actually using these two magnets as two protons. Now, why magnets? Well, magnets are symbolizing the strong force which is working to basically combine them together whenever they are close enough. But there is a repulsion. So, repulsion is this spring, this is a repulsion. It prevents these two magnets from bringing them together. So, what happens actually? Nothing happens, obviously. But if we will start bringing them together against the spring, here is what happens in the real mechanical world actually. Spring is obeying the Hooke's law which means the distance which we are squeezing it by is proportional to the force actually which it exhorts. So, linearly. So, force is proportional to linear extension or shortening. Now, the magnetic force is actually obeying the inverse square from the distance. So, whenever we are squeezing this thing, the force between these two, the attraction, is increasing inversely proportional to a square of a distance between them. But the resistance of a spring, whenever we are trying to squeeze it, is inversely proportional to a distance by which we are squeezing it, right? I mean, considering the lengths. So, my point is that the resistance of the spring grows slower than the attraction of the magnets. And at some point, whenever they are really close enough, magnetic force will overcome the spring resistance and they will just fall on each other. And at that moment, certain amount of energy will be released. And in this case, basically, this is exactly the model how two protons are combined together into one particular nucleus. So, at certain distance, you can't do anything with them. If you apply certain amount of energy to bring them together against the repelling forces of electrostatically positively charged protons, at certain distance, a very small distance, then the strong force will overcome the resistance of the electrostatic force and certain amount of energy will be released. Because, again, the strong force in this particular case has more potential energy in this distance. When it's released, it will be more energy than the energy consumed by bringing together against electrostatic repulsion. So, this is a good model. Now, based on this model, I'll just give you an example of a concrete fusion which might happen. Here it is. Now, I was telling, in the previous lecture, I was telling about certain concept called isotopes. So, certain elements which have certain amount of electrostatic charge, certain number of protons and certain number of electrons, well, the same, presumably, if it's neutral. However, they might have different number of neutrons in the nucleus. And depending on different number of neutrons in the nucleus with the same number of protons, we have different isotopes of the same element and they are slightly different in their qualities. So, in this case, we are talking about two different isotopes of hydrogen. So, the hydrogen always has positive one electric charge, which means there is only one proton. But the number of electrons is exactly the same. But the number of neutrons can be different. So, there is one particular, the most common type of hydrogen. That's one-one. Which means there is no neutrons. So, there is one proton and that's the only thing. So, atomic mass is one. Now, there is a hydrogen which also has one proton, but it has one neutron. So, atomic mass is two. It's called deuterium. And finally, there is another H-hydrogen which has only one proton, but it has two neutrons. So, atomic weight is three. Now, what happens if we will bring together these two isotopes of hydrogen? And here is the reaction which is real. So, we have H. We have one H-2, which is deuterium, plus one H-3, which is tritium. So, two isotopes of hydrogen, one with one neutron and one proton, and other is with two neutrons and one proton. Now, they are converted into helium, which has the atomic mass of two, two protons and two neutrons. Now, this is one neutron. This is two neutrons. This is two neutrons. So, one extra. So, one extra goes out. So, atomic mass with one and electrical charge is zero. That's neutron. It's balanced. One plus one equals two protons. Now, the atomic mass is two and three, four and one, five, which means you have one and two neutrons. This is two neutrons and one neutron. So, it's the same balances. So, this is the reaction which really can happen. Well, most importantly is, number one, we released the energy, and we're talking about why energy is released in this reaction, the fusion. And we have this one, which helps to continue the reaction in some other things. So, it's like a chain reaction, basically. Remember, the same was happening with the fission. Now, this is not such a simple thing, because to bring together from a relatively large distance two nuclei of hydrogen in this particular case is not easy because they are electrostatically repelling each other. Which means that we need a high temperature and high pressure to apply to these two nuclei to combine them together into helium. Well, it's not easy. Now, one of the very important examples of reactions similar to this one is our sun. Whatever happens in the sun, well, it's a complicated reaction, but something similar to this is actually happening. Something which is actually a fusion of certain nuclei into a higher nuclei, and then it actually produces a lot of energy which we are consuming on Earth, and that's basically the source of life on Earth, source of energy at least. Now, in Earth conditions, in Earth's environment, the only thing which we definitely know where it happens is a hydrogen bomb. Well, obviously, if you remember when we were talking about atomic bomb when uranium was split, uranium-235 or plutonium, it's enough actually to give it a little punch, and then it starts the chain reaction. In this case, it's not a little punch. To bring these two nuclei together, we need a very high pressure and high temperature, and one of the ways it's arranged in the hydrogen bomb is to use atomic bomb based on uranium or plutonium to develop this condition of high pressure and high temperature so the fusion reaction can start. So the fission of the uranium or plutonium is causing the fusion of the hydrogen. Hydrogen isotopes, for instance. Now, obviously, we want to control this huge source of energy. Now, we all know that hydrogen bomb is significantly more powerful than uranium-based. Now, it's very tempting to basically do something to keep it under control. Now, the fission is actually under control if you want it in nuclear power stations. We are just slowing down neutrons, slowing down, reducing their number, etc., free neutrons, so we are slowing down the chain reaction. In this case, it's much more difficult. Now, there are some experimental power stations, I should say, I don't know, sources, but every people are developing. But there is nothing actually in the real production mode right now. It's only an experimental stage. They're using certain devices, certain installations to achieve the conditions needed for fusion, the high pressure and high temperature. But again, right now, it's only on an experimental basis. So, basically, that's it. I wanted to talk about fusion. There is not a lot of mathematics here in this particular lecture, but believe me, there is a lot. When people were developing the bombs and whatever they're doing right now, experimenting with controlling the nuclear power, the hydrogen fusion, for instance, believe me, there is a lot of much more complicated physics than whatever I was just talking about. There is a lot of mass, there are a lot of experiments. It's not easy. Whatever I'm just talking about is an extremely simplified version. In the real world, things are much more complex than this. There are different transformations of different elements from one to another. So, the whole thing is for real professionals. The purpose of this lecture is just to explain the main concept of what fusion actually is on a very simple example. Well, that's it. I suggest you to read the textual material, which is supplementing this particular lecture, on Unizor.com. You have to go to the Physics 14 course. It's the part which is called Energy, and the particular chapter is Energy of the Nucleus, which has lectures about fission, about fusion, etc. Okay, that's it for today. Thank you very much and good luck.