hello grade 11 and grade 12 Learners and welcome back to my channel I'm Miss Martins I do physics I do chemistry I do math if you're not subscribed subscribe now for more videos like this in today's video we'll be focusing on electrostatics this is the first video in the playlist and this video is a recap of what you did in grade 10 now grade 11s and grade 12s don't click away you have to watch this video just because we taught this in grade 10 does not mean that we won't ask it in grade 11 and in grade 12 we will so you need to understand this stuff because it will build and the grade 11 and grade 12 look Builds on it but not only that we ask you these types of questions in your grade 12 and in your grade 11 exams and in your tests so I hope this video is helpful let's jump into some grade 10 electrostatics revision jump right into the summary and start off strong with definitions as you should know definitions are a massive part of physical sciences if you don't State the definition correctly you don't get your marks and definitions are supposed to be like level one one or easy questions so grade 10 this is the definitions for this grade the principle of conservation of charge and the principle of charge quantization those are the only two definitions that you need to know in grade 10 in grade 11 and in grade 12 you don't even need to know these definitions you need to know these definitions completely separate obviously if you're in grade 10 this only comes in grade 11 and in grade 12 grade 11s and grade 12s you learn these definitions but gr T these are the definitions for you however it is good to go over these definitions and make sure you understand what it means whether you're in grade 10 11 or grade 12 because they relate to these two formulas this one over here and this one over here and these two formulas although you learn it in grade 10 they can ask it to you and you have to apply it in grade 11 and grade 12 as well so remember definitions you just have to learn it so you may have to pause the screen take this down in your book memorize ize it and then that's it all right now for the formulas as you know you cannot do physics you cannot do chemistry without your formulas and in grade 10 these are the two formulas that you need to know just those two these are given to you on your data sheet on your formula sheet instead of this one you might see a version that looks like this for great T they are the same thing you're either going to get e at the bottom or Q Q E at the bottom they mean the same thing they're the charge on an electron they are the charge of one electron I'll go through what everything else means in a moment but be familiar with these definitions grade 10 11s and 12s you are taught it in grade 10 obviously in grade 10 it's the only definitions you need to know but in grade 11 and grade 12 you still need to know these you still need to be able to apply it in grade 11 and in grade 12 this is what your formula sheet looks like and I hope you noticed that in grade 11 and in grade 12 they don't put this formula on the formula sheet however you still need to be able to apply that formula if need be so if the situation arises where two objects come into contact and electrons are transferred you need to be able to apply this formula so again it's something that you learn in grade 10 but it carries through to grade 11 and in grade 12 so let's focus because this is about a summary um of grade 10 electrostatics we're going to focus on these formula so what I want you to do is when you summarize electrostatics I want you to make a summary of the formula to be used in this section this formula over here on the right is used when two objects come into contact they touch and then they're separated again and the question asks you to calculate the final charge of one or both of the objects after they touch and separate for this formula and maybe we should actually start off with the fact that in electric Statics Q is charge so Q is the symbol for charge so instead of writing out the full word charge we can use the symbol q and the unit for charge is something called coolum kums or C so for example if I say Q is equal to 3 C what I'm saying is the charge of an object is three kums you can get charge being negative or you can get charge being positive you can also get charge being zero you get charge the unit in kums we also get the unit as being something like mums micrum nanocs and pums which I will chat about later but you have to convert these two kums for some formulas right so charge is Q that's the symbol that's the symbol the unit is kums so q1 is the the initial charge of object one Q2 is the initial charge of object two and Q is the final charge and what's important about Q is it is the final charge of both objects so that is very important and obviously the unit for all the q's is kums or C we're dividing by two because there's two objects coming into contact and I will go over this formula in more depth in a little bit but it's important to substit itute the signs into this formula I will explain what I mean later so this formula is basically the principle of conservation of charge that is when we apply the formula so basically says charge remains constant then our second formula is n is equal to Q over Q E remember I mentioned that instead of Q E they can just say e n is number of electrons so we use this formula whenever we are asked to calculate the number of electrons so that's what I said here this formula is used when looking for number of electrons or amount of electrons we can use it to calculate the number of electrons added or removed in order to give object charge or we can use it to calculate how many electrons were transferred or how many electrons move during contact so n is number of electrons Q This is change in charge and I will make a mention of this when we go over this formula and more detail but this Q is not the same as this Q they are different in this formula this Q is final charge in this formula this Q is change in charge and I want you to think of that as final minus initial I will get into that in more detail and as we've mentioned this is the charge on an electron and what's nice about that is the charge of an electron will always always be the same it's always 1.6 * 1019 always always always always always it will never never change right as I said we will get into both of these formulas in a little bit more detail in a second but for now I want to just focus on a very brief overview of the theory of electrostatics electrostatics is all about charge it's all about electrons the first thing that you need to know is that materials so objects surfaces me you everything around us is made up of atoms and atoms contain positive protons so protons are there they found in the nucleus they positive and negative electrons and as you should know electrons are found in the outer orbitals so we also have neutral neutrons but those aren't really involved here what you need to know and this should make sense protons are positive electrons are negative if the number of protons equal the number of electrons the atom is neutral and the material is uncharged so the charge is0 kums like in this case 1 2 3 protons 1 2 3 electrons 0er kums neutral charge and that's what this says over here if you are neutrally charged or uncharged it means you have an equal number of protons and electrons the net charge is zero they often ask you to describe what it means to be neutrally charged or uncharged and that is what you will say positively charged they have more protons than electrons and what's important to state is actually that they have a deficit of electrons so deficit means a lack of electrons they have lost electrons they have less electrons than protons and that's what makes them positively charged now remember electrons are negative so if you lose electrons you're losing the negative stuff leaving you positive negatively charged objects have more electrons than protons they have an excess of electrons which means they have a lot they have a lot more electrons more electrons than protons and therefore are negative and there's a summary of that it is super super super important to note that only electrons can move only electrons so an object can gain electrons an object can lose electrons protons can not move an object acquires a negative charge so it becomes negatively charged by gaining electrons remember if you get negative stuff you become negative an object acquires a positive charge by donating or losing electrons if you lose all the negative stuff you will become positive and again only electrons can move and how does this work electrons can be rubbed off so electrons can rub off from one material to the next so in this case we have a rod it is rubbing against cloth from the arrows in the picture we can see that the rod is losing electrons so electrons are being transferred from the rod to the cloth that means that the rod will have more protons it'll have more protons and electrons it'll have a deficit of electrons because the electrons have left which means that it'll have a positive charge the cloth gains electrons therefore it'll have an excess of electrons and it'll become negatively charged okay so that is how it works the electrons and protons will no longer be balanced okay here's another example now remember I told you that charge is measured in kums remember we said kums is C so for example you can be 3 kums or -2 kums but they might give you the measurement for charge in different units such as Pico kums these are tiny tiny tiny little units of measurement it's kind of like instead of saying meters we have millimeters and you know millimeters are much smaller than meters it's the same thing so mums micro kums nanocs Pico kums this is how they'll show it to you so for example they'll say that the object has three nanocs then you need to know okay cool 3 to convert it to kums I must times it by 10 ^ 9 so what you do to convert it to kums is you just times it by whatever this says over here so another way that I remember it is nano is 9 okay p is 12 micro is 6 and Millie is 3 well ne36 and so on the charge of an electron is this that's a constant and remember with our formulas we call it q e or we call it e a proton has the same charge but opposite so instead of a negative it has a positive now remember the first definition in great 10 that was important is the principle of conservation of charge and what that means obviously you study this if you're in grade 10 you learn this off by heart the definition but what it means is if I have two identical objects on insulating stands and they touch each other and then they separate both of them will end up with the same final charge and obviously this is only true if they are identically sized right and this is the formula that we use in order to calculate it and we've been over the formula before just remember if it's two objects coming into contact we divide by two if it's three objects it's divide by 3 and as I mentioned earlier signs are very important to substitute into this equation so if we have to do this as an example we've got a positively charged sphere a 3 nanocs and a negatively charged spere B which would there therefore be -4 nanocs and they come into contact and they separate and they want me to calculate the final charge on both spheres essentially I need to use this formula because I've got two objects coming into contact and separating so this is the formula that I use then you substitute in q1 is this and I'm going to just change it from nanocs to kums remember you times by Nano 9 * by 10 9 so we got 3 * 109 plus now the second sphere is negatively charged which means -4 * 10 9 this is what I mean by you have to substitute the signs in I say it over here substitute signs into this equation so if one of them is negative you must put the negative in and we're going to divide it by two because there's two spheres that are coming into contact and my answer is -5 * 10 ^ -10 kums okay it's very important now a few things here please use brackets on your calculator when doing this type in the signs correctly you might have to use the small little negative sign in your calculator not the big one if you look carefully at certain scientific calculators you'll see that there are two please type it in carefully make sure your calculator is on the correct mode reset your calcat if you must back to normal that is what you should get now basically what this means is before they touched that was A's charge that was B's charge then they touched and electrons were transferred when they separated again they had the same final charge so this is the final charge a has that final charge and B has that final charge and another thing that I want you to take note of is which way the electrons move when they are touching so remember the the reason they both end up with the same final charge is because when they touch electrons move now which way do you think electrons will move how electrons move should make sense they move from the more negative object to the less negative object so the one with more electrons to the one with less electrons so electrons move that's it electrons move from the object with more electrons so the more negative object object to the object with less electrons so the more positive object it makes sense if you have a lot of electrons you want to give some away you're like oh shame this guy has less electrons than me so I'm going to give it to them okay that is how electrons move and just remember if I have three kums versus five kums which way will electrons move from the three kums to the five or the five to the three well neither of them are negative but this one is more negative it's it's closer to being negative it's less positive if that makes sense so electrons will move from the more negative to the less negative the next Formula that you need to know has to do with the principle of charge quantization now this sounds very fancy it sounds very complicated but basically it just says that every charge in the universe so every object that has a charge that charge is an integer multiple of the electron charge so what that means is you take the charge of an electron and you times it by an integer and you should know that integers are like 1 2 3 4 5 and so on so if I times it by two if I times it by three if it times it by four or 5 or 6 or 1,000 or 1 million that can potentially give me the charge of an object it cannot you cannot multiply this the charge of an electron by something that is not an integer like 1.5 to get you the charge of an object it doesn't work like that it has to be an integer multiple okay what that also means is if I know the charge of an object and I divide it by the number the the charge of an electron then I can work out the number of electrons that that object has extra or that object has in deficit if that is confusing to you don't stress I will teach you what this formula means and how to use it but what you do need to know is that this over here or they can represent it by E that is a constant it's that value and it'll always be that value technically negative but what these lines mean is that we can ignore the negative we can take the absolute value we can ignore the negative and I'll explain what that means in a second but remember earlier on I said that n is number of electrons this is the charge on an electron which is that over there and this that is not final charge remember this Q is not the same as this q no this Q is final minus initial just keep that in mind right when do we use this formula I like to break it down into two situations for my students because it might help them the first situation is when you are asked how many electrons were added or removed from an object to give it its charge so for example if I say my object's charge is 3 and I want to ask you and I ask you how many electrons were removed to give it this charge it doesn't just get that charge remember that's a positive charge I must remove electrons I must take away negative stuff electrons to make it positive and the question could say how many electrons how many electrons must I remove if that's the case we use this formula and just think of it think about it it makes sense we're looking for how many electrons we're looking for a number of electrons which is n the second scenario in which we use that formula is if we have two objects they touch electrons move remember electrons move from the more negative object to the less negative object and then they ask how many of those electrons actually moved when they were touching so did one electron jump over did two move did three did three billion move that's when we use this object and then Q is the final charge minus the initial charge so let's do this example first very similar to the one that I made up a few seconds ago they could say how many electrons were removed to give a sphere a charge of three micro now first of all how do I know that that electrons were removed because electrons on negative and this charge is positive so when we remove the negative stuff we leave it with a positive charge now all you do is you take your formula you write it down you substitute so in this case Q is the charge of the object that's the charge but remember we must convert to kums how do you convert micrum to kums you have to memorize it you times it by 10^ -6 so it's 3 * 10 the^ of -6 and in the place of q e or E we put the charge of an electron yes electrons are negative so you can put the negative there but please please please remember that we are calculating a number of electrons and you cannot get a negative number of electrons and I've said this before in one of my videos and I say it to my classes all the time and I'll say it again in this video if someone asks you and you can think about this question yourself how many chocolates did you eat today you're either going to say nothing I ate zero chocolates or you're going to say one chocolate or two or 10 or 20 hopefully not but you never say negative you don't get a negative number of something you don't say ma'am I ate negative 1 chocolates that makes no sense it's silly it's the same thing with electrons you can only have zero electrons or one or two or three you can't have a negative number so if you put the negative in there it's fine just remember to write your answer as positive so always a positive answer always always always always a positive answer if I type this into my calculator a teacher tip is to use brackets please it makes a difference my students and I have found this over the years and I get one comma 87 5 * 10 ^ 13 electrons it makes sense that it's a big number * 10 ^ 13 is a huge number it must be big now the rule in physics is you can round off to at least two decimal places which means technically you could say 1 88 but I always tell my students my calculator gave it to me like that three decimal places so you may as well leave it like that so in this case that is how I use this formula remember I said that Q is technically a change in charge so change is final minus initial technically this three micrum is my final charge and my initial charge is zero technically cuz remember we remove electrons and then gave it that charge which means initially it had no charge so imagine an object is no charge object is a zero charge initially that's why it's minus 0 we remove electrons and the final charge is this but because we don't because it's zero we don't need to include it there okay I'm just showing you that so if they ask how many electrons were added or removed or how many electrons are in excess or how many electrons are in deficit the C that you use is basically just the charge of the object here's the second scenario in which we use this formula so when they ask you how many electrons were transferred or how many electrons are moved from one object to the other please remember in this case that Q is final minus initial Now read this question carefully sphere a had a charge of three nanocs before it was brought into contact with another sphere so this three nanocs is basically its initial charge initial means the starting charge which you started with then after contact with the other sphere it now has a charge of one nanocs so after contact that is the final charge so basically we had sphere a and sphere B I don't know what sphere B's charges I don't care initially it was 3 nanocs then A and B touched and something happened over there and then afterwards a had a charge of one nanoc B again would also be one nanocon because after they touch remember they have the same charge I don't really care about being in the scenario they want to know how many electrons were transferred from sphere a okay now how how does this work so how many electrons were transferred to or from sphere a how does this work remember we use our formula how many electrons we looking for n so you write your formula always write your blank formula first then Q remember that's final charge minus initial charge so what was your final charge your final charge was 1 nanoc remember that is 1 * 10^9 converted to kums Nano 9 final minus initial we are minusing the initial charge which is 3 * 10 9 final minus initial so you ended up being 1 that's your final minus what you started with divided by the charge of an electron remember whether I put it in as a negative or a positive does not make a difference but your answer for n cannot be negative another very important thing here is the signs are important for this formula as well so if your initial was a negative you must put the negative in there but in this case my initial was a positive so that means that this is obviously going to have to be a positive just keep in mind that the signs are important now use your calculator and I get remember do not put the negative in I get 1A 25 * 10 to the power of 10 electrons there we go and a makes sense once again that it's a big number let's take a look at a combination question that you could get asked We've Got A and B it's clear that these are the initial charges of A and B but they'll probably say that in the little question that I've just cut out A and B are now brought into contact and then separated again and the question wants two things calculate the final charge on a after contact and separation and then calculate the number of electrons that were transferred during this cont contact so let's do number one first how do I know which formula to use we are told that they contact and they separate and we want to know the the charge after the contact and separation and they check they say the final charge on sphere a but technically they could have said the final charge on sphere b or the final charge on sphere A and B cuz you should know that they will be the same so what I need to do is because I'm looking for the final charge after contact I'm using this formula q1 + Q2 / 2 there's two objects I'm dividing by two this formula is one where I absolutely need to substitute in the signs I'm converting nanocs to kums so * 10^9 the formula says plus then Q2 is a negative so do you see how I've substituted in the signs it is extremely extremely important another thing that I often see my students do wrong is they forget to put a plus sign in between these two the formula says plus you have to put a plus sign then remember the big big teacher tip use your brackets and I get -3 * 10^ -9 kums another way that you could technically write this is -3 nanocs because remember nanocs just means * 10 ^ 9 what this means is that initially A and B have the charges that you see on the screen then they touch which way will electrons move by the way they'll move from B to a because from more negative to less negative and then when they separate again A and B both have the same final charge they both have the same final charge my next question remember says calculate the number of electrons that were transferred between the Spheres they mean while they were in contact so what we need to do in order to answer that question is we need to use this formula because they want a number of electrons so remember you write your Formula First always okay it doesn't matter if you say e or Q E then what we are looking for is n remember Q in this formula is final minus initial now you might be like hm ma'am what is the final what is the initial we just worked out the final it was -3 * 10 9us initial now you might be like what what's the initial ma'am the initial is either this charge or it's this charge and you might be thinking ma'am if I can pick which one to use and yes you can you can pick if you want to use this initial or if you want to use this initial you might be thinking but ma'am won't it give me different answers because they're different it will give you the same answer because remember this will be -3 - 2 or it'll be -3 - - 8 it'll end up getting you the exact same answer just please remember that if you decide to use the8 you must put brackets and you must say8 let's use that one just to show you * 10 to the9 so you're either using that one or your alternative let's do both versions here you can say final -3 * 109 there's your final minus initial let's say you choose that one as your initial I will show you that this gets you the same answer remember e is the charge on an electron that's a constant it'll always be 1 6 * 1019 remember you can put a negative there but your answer for n must not be negative so do both of them on your calculator remember to use brackets use brackets it really will make a difference you get the same answer basically what happens is if you calculate just this piece and just this piece you get the same thing but one will be a positive and one will be a negative so this one will be a negative this will be a positive but remember I don't care about whether they're positives or negatives because ultimately my n my answer for n must be a positive it must be a positive one or two other things that's super important for grade 10 11 and 12 electrostatics is that unlike charges attract there's an electrostatic force of attraction so they will move towards each other they attract each other unlike a charges attract so opposite attract they move towards each other like charges repul so they're so similar they don't like each other they move away from one another electrostatic force of repulsion okay another thing the last thing that you need to know is the phenomenon called polarization so I'll use the first two images to explain this is a positively charged rod these balls have a neutral charge okay so they are uncharged what happens when this Rod moves closer and closer but it does not touch these balls is the following the electrons in the balls are attracted to the S remember opposite attract these things have posit positive protons and negative electrons in them remember just because they're neutral remember we said neutral means they have an equal number of protons and electrons so say they've got one 2 3 protons 1 2 3 electrons 1 2 3 protons 1 2 3 electrons they are neutral because the number of protons and number of electrons are equal when we bring the positively charged Rod closer but it's not touching what happens is opposite charges attract so all the negatives move to one side of the ball what that does is that it leaves the one side of the ball more negative so this side of the ball this side of the ball this side of the ball has a more negative charge the other side of the ball the opposite side has a more positive charge because it doesn't have a lot of electrons and that's called polarization because the balls develop a negatively charged pole and a positively charged pole and that that's it for the theory that you need to know please let me know if you'd like to see more you know past paper questions such as these ones um you know in more detail in videos to come in the future I'm so happy to do it please check out my playlist for more electrostatic videos and I can't wait to see you guys in another video very very soon goodbye everybody