hello friends this video on UPI part 20 is brought to you by example.com no room feel from exam please make sure that you have watched all the video still part 19 before going ahead read part 20 let us now talk about the nuclear fusion reaction as mentioned before here combination of two lighter nuclei will give rise to a relatively heavier nucleus and nucleus and here also a large amount of energy will be released huge amount of energy is released now in this case temperature at I mean there is neither important onset in a nuclear fusion reaction what happens in a fusion reaction two nuclei are combining to form a heavier nucleus right now at the same time I mentioned before also that whenever we talk about a nucleus there is a force of repulsion between the protons right because all the protons are positively charged so they tend to repel each other and this repulsive force is nothing but the coulombs repulsive force right so when two lighter nuclei come closer to each other the coulombs repulsive force will increase that means the two nuclei will repel each other right so the coulombs repulsive force becomes our opposition to the fusion right so if we want nuclear fusion to take place then it should take place at a temperature at which the protons would have enough energy to overcome the Coulomb's barrier now this much temperature so for this we need a real high temperature are you getting a point getting my point because since in this case two nuclei will fuse with each other only when they come nearer now when the nucleus are coming towards each other the repulsion between the proton proton will increase so that means this proton should have enough energy to overcome the coulombs repulsive force now Coulomb's repulsive force is also known as the barrier height because in this case the coulombs repulsive force is acting as a barrier to the phenomenon of nuclear fusion so how do the protons how can the protons get that much of energy now if we rise raise the temperature to a very high value at a very high temperature the protons will have that much energy that it can overcome the Coulomb's barrier that is why nuclear fusion always takes place at a very high temperature so this is where the concept of thermonuclear fusion comes into picture what does thermonuclear thermo means Heat nuki so heat plus nuclear fusion that is called thermonuclear fusion so increasing the temperature of the material until the particles have enough energy due to their thermal motions alone to overcome the Coulomb barrier this is known as thermonuclear fusion because in keep on nuclear fusion to take place temperature also plays an important role so what do we do we increase the temperature of the material till the material gains enough energy due to its thermal motion when it has enough thermal energy that we can overcome the coulombs repulsive force then nuclear fusion can take place so therefore this is known as thermonuclear fusion so for thermonuclear fusion extreme conditions of temperature and pressure are required application or example of thermonuclear fusion is energy generation in starch in stars the temperature is extremely high and in the in stars huge amount of energy is generated for example take the best example of the star that is the Sun from Sun we get the sunlight we get such a huge amount of energy and the cause or the reason behind this huge amount of jitter behind this huge generation of energy is nuclear fusion because since the temperature inside the Sun is very I this fusion reaction takes place and huge amount of energy gets released so now we will talk about the energy generation in Sun exactly what happens inside the Sun energy generation in Sun is a multi-step process that means it occurs in different steps so there are a total of four steps involved in the energy generation inside Sun it is also known as the proton proton cycle because this process starts with protons now what happens here let us look at that so let us look at the first step in the first step what happens two protons combine together to form a do Tron which is also known as heavy hydrogen sometimes so this is up when two protons combine to form this Neutron a positron is emitted along with a neutrino and an amount of energy is released which is 0.4 Omega electron volts now what happens the positron which is emitted here this positron combines with an electron and gamma reels are formed plus one point zero two mega electron volt of energy is released now this Neutron which is formed here this two train combines with another proton and this forms helium-3 plus gamma rays plus five point four nine mega electron volts now this helium nucleus which is formed here or this hidrogen then again combine with each other to form helium nucleus plus this proton plus twelve point eight six mega electron volts now the first three steps this is step one step two step three and step four so the first three steps which you see here all these steps occur twice inside the Sun and the last step occurs only once right so now if you combine all these four reactions so what is the net reaction which tells us how much total energy is released in set by the net fusion reactions taking place inside the Sun for that you have to add all these reactions all these equations so what do you get so now if you add these four reactions together you see that a total of some twenty six point seven mega electron volts of energy is released that is four hydrogen atoms combine to form a helium atom with a release of twenty six point seven mega electron volts of energy so if you want to see how four hydrogen atoms combine to form a helium atom with a release of twenty six point seven mega electron volts of energy for that you multiply this equation by two this equation by two this equation by two and then you add all the four equations because these are the processes that take place inside the Sun now if you add them all so what do you get so this is 2 H + 1 this is also 2 H 1 1 so you will get 4 H 1 1 Plus right now I am only considering the left hand side okay so the left hand side will become 2 positron plus 2 electron plus 2 H 1 2 plus 2 H 3 2 plus 2 H 1 1 so let me add it in this so this will become 6 H 1 1 right so in this we are not multiplying it by 2 so this is my entire left hand side now is equal to let us focus on the right hand side so on the right hand side where do we have H 1 2 that is 2 H 1 2 plus 2 positron plus how many gamma you have 1 2 3 so that means it will become 6 gamma plus 2 helium - 3 plus two hydrogen plus helium nucleus plus two neutrino right so if you see this two positron to positron will cancel on both sides similarly this two hydrogen will cancel and this will become so here two hydrogen was there so this will become four right because they have six hydrogen was there so minus two hydrogen on this side so this would become four hydrogen what else will cancel also here if you see you have I am sorry this is not hydrogen this is helium because this helium which is formed here will again combine with another helium to form this so here you will have this as helium right so this two helium here also you have two helium so these two will cancel out so what do I get so the final expression which I get is four hydrogen plus two electron again this will also cancel out to H 1 2 to H 1 T so this will be 4 hydrogen plus 2 electron when you give helium nucleus plus 6 gamma plus 2 nu Plus how much energy zero point four two plus one point zero two plus five point four nine plus twelve point eight six so these things will also get multiplied by two this into two this into to this entry 2 Plus this so this comes out to be twenty six point seven mega electron volts so this is the final reaction or the final nuclear fusion reaction which takes place inside the Sun which shows that four hydrogen atoms combine to form an helium nucleus and with a release of twenty six point seven mega electron volts of energy right so this was the reaction which has been diagram matically mentioned when I was talking about when I was defining nuclear fusion so if you look at that diagram if you go back and look at that diagram you can see the same thing which is represented in the form of diagrams so this I would conclude this lesson on nuclei so what did we study here we studied about the structure of a nucleus composition of a nucleus and size of the nucleus the property of radioactivity which is shown by certain heavy unstable nuclei some of the terminologies related to radioactive related to a radioactive sample like half-life average life and activity of a radioactive sample besides that we talked about a very important thing that is the nuclear energy how do we get nuclear energy out of nucleus what are the two processes of getting nuclear energy that is nuclear fusion and nuclear fusion and their applications so now I think we are good to go to go ahead with some of the prop 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