 Am I audible guys? Everyone are you able to hear me? Are you guys able to hear me? Yes sir. Okay so yes so assignment how to submit you should send me the WhatsApp message of everything what you have done that's how you submit the assignment it is way lot it is lot more easier that way and I asking you to upload on some website you can directly send it over to me Okay so what's going on in school which chapter? So we finished current electricity and we are doing semiconductors Semiconductors you are doing Modern physics hasn't yet started right? Atoms, nuclei and all these chapters No semiconductors So see the idea is to complete this chapter today very little of this chapter is remaining but whatever time we will have after completing this probably we will have around two and a half to three hours we will be doing problems on this chapter okay why we are doing so many problems on the modern physics chapter is because I will not be revising these chapters later on got it so that is the reason why we are doing lot of problems on these small small chapters only so that we are done with it in one go itself no point revisiting it again while revising we will focus on the difficult chapters okay so we will complete this comprehensively at all levels of problems will be done while doing the chapter itself so make sure you are doing the assignments also properly and submitting it you have to practice lot of questions because treat as if you are not going to revise this chapter ever so finish this off once for all okay so that you save lot of time later on if you assume that later on if you assume that later on you have to revise this chapter then that revision won't happen and you will not be able to do the chapter also properly in the first instance itself alright so any doubts till now with respect to this chapter anyone has have you done the assignment that is that I should actually ask that question then only doubts will come right those who doesn't ask doubt doesn't do anything that's why doubts are not there but anyways so last class what we did was we introduced what is the nucleus okay we introduced mass energy equivalence which is the basis of everything in this chapter what does mass energy equivalence say Pratham what it is mass energy equivalence mass can be converted to energy that's all can energy be converted to mass yes sir I think so yes even energy can be converted into mass okay so you know what is the implication of that it has a very wide implication that if there is an object which has a velocity okay what we say that kinetic energy we say kinetic energy of an object moving with velocity v is half m v square alright but in reality kinetic energy formula is a hypothetical formula okay this is something which we have assumed to be this in reality what happens is that if the speed of an object increases its mass increases so mass becomes m0 divided by 1 minus v by c whole square where v is the velocity okay so if certain object is moving with velocity v its mass increases so at rest the mass is m0 this is called rest mass okay I am talking about mass energy equivalence little bit here before starting the today's topic so all of you focus here till now we just like we have learned about the bonds formation of bond double bond triple bond exothermic reaction is formation of new bonds potential energy and all that and later on we identified that it is nothing but conversion of mass into energy which leads to exothermic reaction similarly even kinetic energy is a higher order concept higher order as in it is not a basic concept at the core level at the base level what is happening is that whenever an object is is having some velocity its mass becomes equal to m0 divided by this okay so its kinetic energy simply will become equal to mass m minus m0 into speed of light square so if an object increases its velocity its mass which was m0 earlier increases to mass m and whatever is the extra mass into c square that will be its kinetic energy alright I understand that this is something completely new and weird to you till now everybody was talking about kinetic energy to be equal to half mv square and that's how we have proceeded but you know I am trying to explain the same thing the energy concept with respect to mass energy equivalence okay so a clock which is running is heavier than a clock which is not running okay any moving part by mass energy equivalence what happens is that some energy gets converted into mass alright so this is what happens at the very very basic level okay so that's how important the Einstein relativity concept is okay so this is mass of an object whose rest mass is m0 and who is moving with velocity v mass increases by this much and difference in the mass difference between the mass at rest and whatever the current mass into c square will be its energy which got converted into mass while it is moving everybody understand this whatever I have just said is it clear Aditya is it clear to you Ayush yes sir yes sir okay so there are some numericals on this concept also this chapter makes you think in a different way same thing which you already know this chapter makes you think makes you look at it in a different way okay so I hope this is not very confusing to you it is as simple as you know some energy if there is more energy in an object it automatically means it has more mass because you are supplying energy that energy will get converted into mass okay and how much mass will become mass will become this much m0 divided by root over 1 minus v by c whole square this is given by the Einstein understood Dhyan any doubt sir sir we can use that formula the mass m in the kinetic energy equation sir what we can use like this mass m this one yes sir this doesn't work if your speed is close to a speed of light don't use that it's an approximation even if we use m is equal to m0 by 1 minus v by c square say it again sir even if we use m is equal to m0 by root 1 minus v by c square then also we can't substitute that no you can't substitute that it is an approximation you know what happens you know since you are talking about it it will become m0 1 minus v by c whole square to the power minus half then if v is very less than c minus half will come inside so there comes the half factor okay so this formula comes from the approximation of this okay but do not try to mix these two things otherwise you will end up confusing yourself only okay sure that you assume that this is the kinetic energy formula this one okay but sometimes it is written like for example they will tell you rest mass is this much okay and they will say that electron is moving with 0.5 times speed of light then what is its kinetic energy so that type of question you need to identify and then use this concept don't try to mix up otherwise it will be a confusing thing to you right now yes okay so let us continue what happened guys where are others do you have some ut's coming up yes sir saturday so today is Thursday which ut chemistry is scary chemistry ut so I hope you are not thinking about chemistry while sitting here so chemistry isn't by the teacher so like the connection is very strict so we have to study it very properly that's good chemistry actually the good thing about chemistry is that whatever you are doing in school everything will get translated to whatever is useful in JEE or NEET whichever exam you are writing because the school level and JEE level they are not very far apart main level at least so studying for school will help definitely but then not bunking physics classes and then studying chemistry okay so I can't stress more about the fact that how important these classes are at least the modern physics which is giving you very very easy marks anyways so I can't pull everyone by hand right can just say so last session we have done discussion of the nucleus its mass its size then we discuss about existence of neutrons then we discuss about the stability of the nucleus how stable particular nucleus is stability of a nucleus is caused by a mysterious strong force called nuclear force which is attractive because of which only two protons are so close to each other it is stable so because of the nuclear force which is strong force nucleus is stable but it is seen that the nuclear force which is very very strong it exists for a very small distance also okay for example 10-15 if your distance is slightly more than 10-15 meters which is the size of nucleus nuclear force becomes zero immediately and hence stability is limited up to the size of the nucleus which is very very small and one reason why nucleus is small is because of the nature of nuclear force itself which is applied to a very very small distance and because of which only when nucleus becomes bigger the size when it becomes bigger it tends to gain instability also because nuclear force won't be able to hold each and every nucleon inside the nucleus nucleon is by the way proton and neutron both of them are called nucleon okay so once we determine that nucleus bigger nucleus can be unstable we learn that these bigger nucleus can spontaneously go towards the stability the most stable nucleus we identified was iron so these heavy nucleus tend to go spontaneous disintegration and daughter nucleus are formed you can say product and reactant also so the because of this spontaneous reactions there might be some radiations coming out and it is seen that typically three different kinds of radiation that come out alpha beta and gamma and depending on these three radiation we have named alpha decay gamma decay beta decay like that okay so then we have also discussed something mathematical about all of this we determine the rate of decay which is rate at which the number of nucleus are decreasing is proportional to the number of nuclei at that moment itself so we got a differential equation which says that dn by dt is equal to minus of lambda times n okay after this we have solved this differential equation and we determine that ln l by n not is equal to minus of lambda into t so from here we got n is equal to n not e to the power minus lambda into t okay we also derive that half life of the nucleus what is a half life amount of time taken by the number of nucleus to become half is this much okay which is ln 2 by lambda only put n equal to n not by 2 you will get this and we have found out that the average life is 1 by lambda okay all of this we have done and before this I am just listing down all the mathematical things we have before this we found out that the radius of nuclei is r equal to r not e to the power 1 by 3 what is the value of r not anybody knows this how much it is 1.2 into 10 to the power minus 15 meters this is the radius of the nuclei okay so and from Einstein relativity equation we got mass energy equivalence this also implies mass is equal to whatever energy an object has divided by c square so some energy can get transmitted as mass using this equivalence reaction equivalence works both ways energy can be converted into mass mass can be converted into energy we have learned that if one unit of mass converts into energy how much energy to liberate how much it was 931.5 mega electron volt okay all of these things should be on your fingertips okay you can also say 931 also just 931 is also enough okay we also learn about the binding energy of a nucleus is equal to the mass defect it has which is the atomic number into mass of proton plus a minus z which is mass number minus atomic number that will give you neutron so mass of neutron okay minus mass of the nucleus this is the mass defect and delta m into c square is your binding energy okay binding energy per nucleon is what this divided by the mass number which is number of protons plus neutrons so this is the mathematical part of it which we have learned why I have summarized this because let us take some numericals then we will discuss whatever is the pending portion of the chapter so very little is left so let us first do some questions on these anyone has any doubt quickly ask no one has any doubt how is it your uts are starting from saturday or you are in middle of a ut starting from saturday sir starting naffles students are there naffles yes sir shankin is there shankin where is shankin bro here is shankin shankin skanda who else where is anurag yes sir how to go about this this is equivalent to potential energy between no one knows trippan do you know how to solve this we have to consider them as point charges situation at their centre then we can find the distance between them see you have to find potential energy between 6 protons and 6 protons and the distance between them is centre to centre distance between 2 nucleus which is 2 times the radius of the carbon nucleus and the radius of carbon nucleus is r equal to r0 1 by 3 now do it 1.2 into 12 to the power 1 by 3 femtometer this is 2.74 femtometers now do it you have to answer in electron volts okay electron volts you are dealing with just 2 atoms this is the distance between 6 6 protons they are touching each other these are 6 protons neutrons I am ignoring because neutral particles won't have electric potential energy they may have nuclear energy but not the electric potential energy what is the formula for potential energy that you can use k times q1 q2 by 2r is 9 into 10 to the power 9 q1 and q2 both are 6 times charge of a proton which is 1.6 10 to the power minus 19 whole square actually that divided by 2 into 2.74 into 10 to the power minus 15 if you divide this by charge of one electron you get it in electron volts okay this and that will be gone how much it is roughly in electron volts anybody got it this chapter is all about calculation calculation is main part tell me what it is if anyone has any doubt please type that out also if you have doubt don't hold your doubts to yourself today most of the time we are doing problem practice only at the start itself don't start holding your doubts back this is around roughly 9.6 mega electron volt okay don't write that m should not be a small m okay trippan no no no mega see this is 9 this is 19 will become minus 10 then 10 to minus 15 goes up it will become 10 is for 5 okay yes okay everyone understood anyone has any doubt quickly type in now just just a small thought here suppose these two nucleus have to fuse into each other suppose fusion reaction should happen between these two nucleus you can say this is like your activation energy you know what is activation energy this is like a potential barrier okay it is like this this much barrier this much potential energy one has to supply for them to reach here so that nuclear forces become stronger and then reaction between these two nucleus will happen everyone understood this point also this is that is the reason why you don't see fusion reaction happening at a very less temperature the stars is having fusion reaction hydrogen and hydrogen atom they fuse and create helium okay so fusion reaction to hydrogen atom should come very close to each other and before nuclear force starts applying they will have lot of repulsion because of the like charges between the two nucleus one has to overcome that and how we overcome that by creating lot of kinetic energy in the nucleus kind energy of an atom means its temperature only so we'll talk about this thing again when we talk about the fusion reaction now let's move ahead something very familiar we have done something similar already and first write down the reaction 26 proton 30 neutron creates the iron nucleus binding energy is nothing but energy released in this reaction did you find the mass defect how much it is first tell me mass defect what's the mass defect anybody else got it they on got something others mass defect is what 26 into 1.00 783 plus 13 to 1.00 867 minus 55.9349 how much it is 10.5 no okay see mass defect you guys are getting different answers I can see that everyone is getting different from mass defect do it yourself do not refer to any book or anything else you are not doing anything useful mass defect is 0.528 78 okay see the problem you can see many of you have gone wrong many alright you have not gone wrong in concept you have gone wrong in the calculation part of it so you need to be very very careful with this otherwise no point knowing the concept you are as good as somebody who doesn't know anything okay so what is the answer in mega electron what should I do once I get the mass effect which is this then what what is the binding energy mass defect into C square is fine but if you want to multiply by C square you need to convert this into kg right now it is in units into 931.5 into 931.5 if you do you will get it in mega electron volt tell me what it is do this calculation okay do not feel you know frustrated by the kind of calculation you are having this will benefit you in many ways quickly find out what it is let's see whether all of you are getting the same thing it is useful to you are you doing anything just sitting there so why not answering what is the answer okay all of you should answer all of you should answer I will tell you the exact thing what it is 492.54 okay this much MeV how much binding energy per nucleon how to find out per nucleon anyone this is the binding that divided by 56 which is equal to what you guys know it already the firing is 8.75 MeV okay this is like the most stable nucleus binding energy per nucleon okay so you can check whether it is this one or not so this divided by 56 is binding energy per nucleon this one decay constant you can what is the unit of decay constant by the way lambda unit says per unit time that could be per day per year whatever I mean you can answer lambda in terms of per day also just fine you don't need to convert every time into seconds also it also depends on you know the kind of options in front of you if options are in days you write it in per day herds don't write lambda in herds okay although the herds and lambda both units are per second but herds means something is oscillating don't use that okay Anjali what is the answer lambda what have you done 0.693 divided by what divided by half life half life is 0.693 by lambda so lambda is 0.693 by half life isn't it that divided by 2.7 this is this you can find out in per day how much it comes out that's about 0.26 0.256 this is A B average life 4 days okay 4 days average life formula is what T average 1 by lambda right 1 by lambda so it is definitely less than 4 less than 4 it is 1 divided by 0.25 is 4 this is 1 divided by 0.256 but yeah close to 4 only so this will be around 3.9 days Ravi Kiran don't use calculator C do the C activity you have to find in BQ what is the formula for activity what what and lambda activity is nothing but rate of decay right dn by dt which is lambda times n mod of dn by dt is lambda times n what is n how you get n 1 milligram of that that is 10 is power minus 3 gram that divided by 198 into 6.023 10 is power 23 all of you understand that this is n that into lambda lambda is 0.256 this per day per second you have to do that is 24 hours 60 minutes 60 seconds this see how nice it looks calculation what is the answer for this 198 roughly you can tell denominator you can take close to 200 when you increase the denominator slightly you can increase the numerator also tell me what is the answer I calculated in terms of days convert those per second multiply that with this 24 into 16 to 60 damn getting it damn okay Tirpan got something and that is not correct now everyone is getting different no wait that is correct Tirpan got it correct there is roughly 6.73 into 10 is power 13 this calculation but in the book it is written something else probably in the book the answer is not correct okay so this is the answer things are clear just it is about the calculation okay let's take see I don't have many questions okay you have to practice them if you practice them right now you will have to practice a lot lesser number of numericals when exam comes but if you don't do it right now you may have to work three times more later on focus here practice each and every question you have here Arpita will tell the answer for this others also keep doing it you can message Arpita what is the answer Arpita is there or not name is there Arpita is reading chemistry while being in the class alright so okay good I can see many of you got it correct so some of you are making sillier also alright so radioactive sample has this much nuclei at certain how many nuclei will still be at the same active state active state means what active state means remaining ones okay the remaining ones the remaining one after one half life is N0 by 2 after 2 half life is whatever remains divided by 2 so after 2 half life N0 by 2 square will remain so how much will remain 6 divided by 4 into 10 to the power 18 which is 1.5 into 10 to the power 18 active nuclei will remain so that is the answer okay I can see almost everyone got it questions only but anyways let's do this counts means disintegration per counts mean disintegration alright so disintegration per week is given when you burn the charcoal does anything happen to the nucleus everyone when you burn it CO2 is released does anything will happen to the nucleus of carbon nothing will happen to the nucleus burning is a chemical reaction carbon electrons will take part in the reaction it will react with oxygen okay nucleus will remain that only so what is counts I know if you are stuck counts is disintegration disintegration per week is given these things are given like this should I do it now log of 1.5 yeah that's fine you tell the answer in terms of log that is fine no problem so we can assume N0 is the same for both Terpan what is your answer not getting it number of initial nuclei will be same or not for both of them when they started disintegrating can I say that number of nucleus are same for both yes sir equal masses right equal number of nuclei is when they started okay should I solve it now or should I wait none of you got it correct till now Terpan thinks my speaker is on mute can you speak Terpan then I will check I can hear yes sir okay I will solve it now there you go number of A will be equal to whatever was the initial number e to the power minus lambda into T1 after T1 times its activity is becoming this let's say that is T1 after T2 times same number of nuclei is N0 will become NB which will be equal to N0 e to the power minus lambda into T2 okay I don't know what is N0 but I know that is equal so N0 N0 will be same so I can just divide it okay when I divide it I will get NA by NB is equal to e to the power lambda times T2 minus T1 this I get now NA by NB is what NA by NB I can multiply lambda both sides lambda NA by lambda NB this is equal to this and that only okay so lambda NA by lambda NB is equal to rate of disintegration 2100 divided by 1400 this is equal to e to the power lambda times T2 minus T1 okay and you can see that there is a division happening here it is dimensionless so I don't need to convert week into seconds when I divide the multiplication factor will become same alright now 7 2's are 7 3's are 3 by 2 is this getting it so 1.5 is equal to e to the power lambda T2 minus T1 take natural log both sides ln of 1.5 is equal to lambda times T2 minus T1 so delta T is ln of 1.5 divided by lambda now lambda is what lambda is 0.693 into T half half life is 5730 years so this is how carbon dating is done this is the difference in the life of their samples anybody got this one this thing yes okay have you understood this Dhan got it but it proceed next this we are done this is interesting capacitor circuit is different okay so there are two different things happening here did you guys get date for your pre words in school second you usually it happens in the month of first week of November it used to happen so planning to bunk centrum classes for when the pre word starts yes so we are going to have crash course during that time difficult to manage but that's anybody close to the answer you can give answer in terms of log in terms of e to the power whatever it is there okay but at least little bit of simplification you can do don't give answer in terms of 3 divided by 5.6 like that whatever you can do by hand calculation do it and then whatever remains you can answer yeah you can assume initial number to be N0 that is constant anyways ln 2 is 0.693 nobody else okay listen here sir one second sir these formulas you know or not e to the power minus t by rc charge is decreasing with time ratio should be constant n by q should be independent of t what is the condition so that they are independent of t what should be the condition what do you think coefficient of time should be 0 right then only it will be independent of t so 1 by rc minus lambda should be equal to 0 everyone understand this how this comes if it has to be independent of t type in quickly have you understood this r is equal to c lambda lambda is ln 2 by t half t half is given right half life is given no average life is given so lambda is 1 by average life so this divided by 1 by c lambda I was just checking whether you guys are awake 1 by c lambda so 1 divided by c is 10 ratio power minus 4 into lambda is 1 by 20 milliseconds 20 into 10 ratio minus 3 so that is 200 ohms okay so this is the mistake sometimes you do you are used to seeing the half life given suddenly instead of half life average life is given and in the questions guess what there will be an option in which the same thing will be treated as half life so you will make error there okay like what Terpun did right Terpun so I think you can see that even those problem looks huge but then they are very simple questions they are not difficult when you look at the solution this will do later on this is 80% of chances if there is a question from this chapter it will be from radioactivity it's like Young's deficit experiment how important that was in wave optics similarly how radioactivity is important in this chapter have you done this you know how to solve it get the correct answer I am just checking whether you can calculate accurately okay I want average life in terms of years tell me in years what is the average life that will make more sense how you convert this into years that divided by pi how much it is how many years 6.49 into 10 is power 9 years okay so 6 billion years is the half life okay now B part what is the half life how you calculate half life from the average life D half is how much times average life 0.693 0.693 half sorry average is D half how much it is this into 0.693 is how much quick very quick tell me 4.5 into 10 is power 9 years roughly do it yourself C part what is the answer how many half lives is 9 into 10 is power 9 how many half lives in 1 half life it becomes half in 2 half life it will be 1 by 4 number is 1 by 4 activity will also be 1 by 4 activities proportional to number activities lambda times n radium chloride is the compound which madam Curie has extracted from rock or something is chlorine radioactive here or only radium is radioactive only radium only radium okay usually radioactive elements are very heavy they go spontaneous disintegration chlorine is very light I mean the formula is straight forward you need to find dn by dt right this is the activity which is equal to lambda times n okay lambda is 0.693 divided by t half that into n show me got something others how to get number of radium nucleus n is odd you have 0.1 gram of radium chloride so 0.1 divided by molecular mass of radium chloride not the atomic mass of radium okay so that is 226 plus 2 times 35.5 this into Avogadro number everybody understood this and half life you have to write in terms of the seconds that is 1602 into pi into 10 isopower 7 so get the answer now substitute it here there multiply that at 0.693 and tell me what is the answer such a nice calculation pen got something there is no 3 pen that is not correct very very less 3 pen actually check what mistakes you have done only calculation mistakes you can do now show me got something no that is not correct 3 pen got something again yes that is close to the correct one good at least you guys are trying that is good 28 into 10 isopower 9 every second these many nucleus are disintegrating or decaying radium okay I will move forward only one or two questions are remaining on radioactivity alright those who haven't tried to this so what is the previous answer 2.8 into 10 isopower 9 thank you sir you can answer in terms of log also sir sir in such kind of questions should we take one month as 30 days or 31 days 30 take it as 30 you like your calculations then no one sir I think they want us to take a month as 28.6 okay otherwise some log and all will come complicated okay so but then that should be written you can take your half life to be 15 days now do it 200 rupees 3 pen will buy for 200 rupees something also spend 200 rupees don't keep it nearby very very harmful 20 the answer is 187 rupees in the book but then we have modified it so that's fine I don't need to solve this right so in 2 in 2 half lives you'll have and not becoming and not by 4 so even activity will be 1 by 4 that is 200 rupees okay is done how many radioactive we have 1 and 2 just 2 more even tritium is radioactive though it is a light atom for party what is the answer what is the answer type it out could not understand the atom yes that's correct you know directly number is given to you half life is given so you should not make here at least it is not good if you make mistake simply this kind of thing 7.1 into 10 is power 14 it will be sad if you get this wrong okay then nobody else is responsible for it simple multiplication be part number of nuclei that decayed in next 10 hours how you do this okay you don't need to completely solve it you have to do it like this n equal to n0 8 the power minus lambda t okay yeah to put the value of t over here lambda is given lambda you can find out and n0 is given to you you find n which is the n is number of nuclei that are remaining n0 minus n is the answer n is not the answer n is remaining nuclei got it similarly you can do the c part also alright c part though you can c part you can answer actually it's some it is multiple of two right so getting the answer for the c part you don't need to do any complex thing there immediately you get it wrong otherwise yes show me that's not correct no so that is not correct number of decays in next 6.15 years it is not half life if I ask you number of decays in next 12.3 years then 2 into 10 spot 23 is correct it's not in half life okay so let's see how to solve this ln n by n0 is equal to minus lambda into t now I can write this as ln n by n0 to be equal to minus of ln 2 by half life so it is minus of ln 2 t is half of the half life so ln 2 by 2 will come right so ln of n by n0 is equal to minus of ln 2 root 2 fine so n0 by n is equal to root 2 so n is equal to n0 by root 2 so this is the number of nuclei that are remaining number of decays will be n0 by root 2 everybody understand this how it comes type it quickly then move ahead okay last question on radioactivity last one after this we are not going to do any question do you write your J mains remember that I mean we as in I will you have to practice question on carbon dating I think it is simple okay so I think here you have to take log and all dn by dt is lambda times and not and not is the number of nucleus in one gram this is given as 15.3 and it is per minute that's fine we are going to anyway take the ratio of it dn by dt is lambda to n which is 12.3 per gram per minute so we have taken for one gram what it is so when you take the ratio we will get n0 by n is equal to 15 by 3 divided by 12 by 3 so ln of n by n0 is actually ln of 12.3 divided by 15.3 this is equal to minus lambda times t and I can modify it and write it like this ln 12.3 divided by 15.3 this is equal to minus of point six nine three divided by five do I need to convert the time into seconds everyone can I write like this will I get t in years if I write like this I will get t in years this right hand side is dimensionless anyways so you can have any dimension you can have any unit for lambda and t when they multiply anyway it become dimensionless this into point six nine three ln of 15.3 divided by 12 point this is the answer alright so this is what the radioactivity is all about up till here we can now continue with the chapter what is the time right now it is yeah we have 20 minutes before the break let's continue with the chapter and then we will see what other kind of numericals that are there in this particular chapter okay I hope no one has any doubt here if there is quickly type in fine so talking about the radioactivity we now know that there are three kinds of radioactivity that exist and the name is with respect to what particles they emit so let's quickly talk about them one by one the first one is alpha dk wherein alpha particle is emitted alpha dk so one popular example of alpha dk is 238 uranium its atomic number is 92 converts to thorium plus alpha particle alpha particle is helium nucleus which has two protons and four nucleons so what will be the atomic number of thorium what it is 234 and 90 this is 90 and this is 234 okay in fact you can see here for two protons are gone with the helium so remaining protons are 90 so every time alpha dk happens every time it happens the atomic number will go down by 2 and the mass number goes down by 4 okay there are numericals on this as well of course it will not be as straight forward as this looks they may mix the beta dk also along with it but this is the starting point how much heat will be emitted in this reaction any guesses suppose masses are given to you mass of helium y and x they are given to you then how much heat will be emitted mx minus my minus mass of helium into c2 understood what is it out okay so let's take a numerical then right we have I think a numerical from your textbook only this is part 2 right you can see our first focus is your school and then we go up to higher order questions directly from your school book do it so that got for the first one and that is not correct the reaction is the same reaction which we have just written uranium 92238 it emits an alpha particle thorium gets created yes ravi kiran fine skanda what is that electron volt ayush is that electron volt how come ayush and skanda getting exactly same answer are you guys talking to each other no no it can't be this much energy skanda one reaction you're talking about one reaction one atom creates 10 is power 14 joules imagine one mole of atom how many joules it will create entire earth could be utilizing that power for generations to come how to solve this question first you need to find the mass defect as always okay mass defect is helium not the helium one sorry mass defect is by 238 first tell me the mass defect how much are you getting mass effect everyone this minus 234.04 363 minus 4.00260 what is the mass defect 0.00456 0.00456 units is the mass effect so energy release will be how much this into 931.5 mega electron volt how much it is tell me it's 4.25 MeV this is the energy release in one reaction there can be many reactions happening many as in 10 is what 23 reactions might be happening for one mole okay so don't underestimate the amount of energy release this is only for one reaction okay this is a part B part what is the answer what is the mass defect in the B part if uranium 238 emits a proton what will happen it will become 237 and 91 it will become palladium plus proton mass effect is how much over here mass of uranium minus mass of PA plus H how much it is how much it is mass effect negative right minus of 0.008 so what does it mean it means that it has to you need to supply energy so that energy can be converted into mass can it happen spontaneously any endothermic reaction can happen spontaneously everyone understand remember the sad remember how much noise you guys to use to make in class 11 I had a hard time keeping you quiet now everyone is so quiet I want you to talk right on beta decay okay beta decay can be of two types beta minus beta minus decay wherein electron is emitted beta plus decay wherein a positron is emitted okay so how electron gets emitted we are talking about nucleus here nucleus emits the electron what happens is in beta minus decay a neutron converts to proton and because of charge conservation one electron has to get emitted inside the nucleus neutron converts to proton and one electron is emitted and there is one mysterious particle also that get emitted which is anti neutrino so this is beta minus and beta plus decay any guesses what will happen in beta plus E plus should be emitted no one proton converts to neutron charge conservation will happen one particle which has same mass as that of electron but a positive charge will be emitted so you can't call it proton plus neutrino okay neutrino and anti neutrino are mysterious particles they are mystery to everyone now also they are so mysterious that they I mean they will not found initially they were like they when they emit they can cross the entire earth from one point to the other point just like that and doesn't interact with anything okay so later on only by some process which I am not aware of they found to know they got to know that there is an neutrino and anti neutrino particle that also come out okay so this is the reaction that happens now if this is the reaction suppose I talk about the beta minus emission of the phosphorus what will happen everyone write the reaction for beta minus decay beta minus decay of phosphorus what will happen everyone write down phosphorus will become what proton is increased so it will become sulfur mass number will be 32 only neutron converts to proton so number of neutron plus proton remains same this plus electron plus one anti neutrino this is the reaction beta minus decay okay now can you write down the beta plus decay of sodium let's say 11 22 what will happen everyone write it down all of you tell me what will happen what will happen is atomic number how much it will become in beta plus one proton converts to neutron so atomic number will be 23 atomic number 23 number of proton is 11 one proton got converted to neutron so protons have decreased but number of protons plus neutron they are unchanged this will become neon 22 so you can see that chemical reaction only changes the electronic configuration here it changes entire existence of it there is a beta plus okay so this is these are the two examples one is beta minus other is beta plus and one very important thing point to note here is that that mass number is unchanged in beta emission whether it is beta plus or beta minus mass number remain unchanged in beta emission in beta does element always change the you can see in beta minus atomic number has increased by one beta plus atomic number has decreased by one so the element changes okay so like this if you can convert mercury into gold also if mercury mercury atomic number is 80 so if it loses one proton or if it undergoes beta plus emission mercury can become gold but that doesn't happen so next is the third type of radioactivity gamma gamma decay gamma decay so like I said gamma is a is an em wave there is no change in atomic number or mass number because of this no change in atomic sorry mass number and atomic number okay usually usually followed by alpha decay and beta decay so after alpha and beta decay then gamma decay happens okay now can you tell me gamma decay once it happens will the mass of the nucleus remain same decreases or increases after gamma decay say it again decreases decreases why because em wave is it has an energy so correct so some mass has to get converted into the gamma radiation alright this is what at the core level things are okay good so it would now start thinking in that way in fact in this chapter this is what they want you to think like they don't want you to talk about bonds they don't want you to talk about potential energy and all those things it is entirely mass energy equivalence entire chapter okay so one example is this suppose there is a cobalt here okay I'm taking example from your textbook only there is a cobalt this cobalt I'll first plot these levels so what happens is cobalt undergoes beta minus decay what happened to atomic number increases or decreases by one increases increases right beta although it is minus but it increases electron is emitted that's why beta minus so what it will become 28 nickel nickel it will become 28 nickel 60 this is in excited state then this is nucleus of the nickel it is here alright what will happen is that it can go to this energy level it can then transition to that energy level also alright the lowest level is a ground state so this one is the second excited state put one star here and this is the ground state of the nickel nucleus so something like what electron undergoes okay electron also has similar transition that happens from content number two to one three to two like that okay so this energy difference in terms of electron level we are just couple of electron volt but here the nucleus energy level when transition happens is of the order of mega electron volt so the difference in energy level for the nucleus transition is very very high okay tell me all of all these three nickels whose mass will be highest double star single star or no star this one mass is highest in fact this mass minus that mass whatever is a mass difference will be released as this energy okay so you can see when we talked about electron we were talking about okay whatever is the sum of counting energy plus potential energy at n equal to two minus sum of counting energy plus potential energy at n equal to one will be the energy of the photon that is how we used to talk okay but here we are talking in terms of mass so excited state mass is slightly higher when it transitions to lower state some mass gets converted into energy we don't talk about potential energy in counting energy even though potential g counting energy is there that is represented in form of in the form of mass itself okay so these are the three DK's that are there okay alpha beta and gamma DK we need to discuss about fusion and fusion reaction also so we can take a small break come back discuss about a fusion and fusion and then we can take up next type of questions from this chapter okay let's take a small break right now it is 606 meet after 15 minutes 621 come back in time okay all right you can hear me everyone one thing is that these energy levels are so big that the frequency corresponding to it is larger than that of x-rays okay they are very very strong EM wave you can see fine