 Hi, I'm Zor. Welcome to a new Zor education. I would like to continue talking about electricity. In the previous lecture, we were talking about what exactly is the carrier of electricity and its electron, and electrons can be in excess of the same number as protons are or can be in deficiency, in which case we will have negative or positive electric charge. The question is right now, in this particular lecture, how to measure electric charge? So we know about its existence, it's based on certain excess or deficiency of electrons, but now we would like to measure it. Okay, now this lecture is part of the course called Physics for Teens and it's presented on unizor.com. I do recommend you to watch this lecture from the website, because every lecture including this one has detailed notes, and notes can be in some cases a little bit more detailed than whatever I'm talking about. Also, the website has exams in many cases, and it's completely free, no advertisements, nothing, so I think it's much better to use the website. And besides, it's a course, so if you just found one lecture, it's one lecture, but on the website you will find the course, which means it has certain sequence of offering certain information which is related to each other. One lecture is obviously based on another, and as I was just talking about right now, this lecture is based on the previous one. The previous one, we were explaining what electrons actually are doing. They are carrying the electricity, and now we were talking about how to measure it. Okay. So how to measure the amount of electricity? Electric charge. How to measure the amount of electric charge? Well, let me start from the end, if I may. Right now, with all the knowledge which we have right now, especially the fact that it's electrons which are carrying electric charge, and they may be in excess or in deficiency, which makes negative or positive electric charge. What's the most natural, I would say, way to measure electric charge, but just to count number of electrons? I mean, certain electrons are in excess of number of protons, and this excess of electrons, the number of these electrons is a very good quantitative characteristic of the charge. Or if it's a deficiency of electrons with positive charge, obviously the number of electrons which are deficient, which are less than the number of protons in the atoms of this object, basically, gives you exact number of exact amount, the measure, if you wish, of the positive charge. Well, what's the problem with this? Well, the obvious problem is that electrons are very, very small, and it's kind of difficult to measure something in such a very, very small quantities, because the numbers which we will be dealing with in normal physical experiments or life, if you wish, these numbers will be really huge. So instead of using the amount of electricity in one electron as the unit, physicists have decided to use the bigger unit, proportionally bigger, which is called Coulomb. Well, it's a French word and different, in different places it's pronounced differently. I think British is more like Coulomb, in America is more Coulomb, but whatever it is, doesn't really matter. This is the unit which physicists have decided to use, and in this a much larger unit than the charge of one particular electron. One electron has a charge something like 6, 0, blah, blah, blah, the exact number is, by the way, in the notes for this lecture. There are many, many different digits up to the decimal point, times 10 to minus 19 Coulomb. So this is a charge of one electron. So basically it's like a definition right now. So Coulomb is the amount of electricity, it's such a unit of amount of electricity that the amount of electricity in one electron is this particular number of Coulombs, which is very, very small, you see 10 to the minus 19. Well, natural progression of this is the question, okay, how many electrons do we need to amount into one Coulomb? Well, you just have to do the reciprocal number. So if you will have one over this 1.6, blah, blah, blah, times 10 to the minus 19, you will have something like, what, 0.6 10 to the 19, or 6 to the 10 to 18, doesn't really matter. This is the number of electrons which combined together have the charge of one Coulomb. Again, it's obviously a very big number. And what's basically interesting about the whole measuring of electric charge is that this type of a definition, which from contemporary viewpoint seems the most natural, I mean it doesn't really matter whether my unit is the amount of charge of one particular electron or this number of electrons, it's still proportional to the number of electrons wherever you are and that seems to be very natural considering electrons are the carrier of the electricity. However, when physicists first started actually thinking about measuring the electricity and different actions related to electricity, like electric current for instance, they went a different way to measure the electricity. Primarily, it was related to the fact that at the time they didn't really know everything we know about structure of the atom, about measuring electrons and etc. So they did not have that apparatus. So they had to really start measuring electric different electrical characteristics using something which they could measure using their experimental equipment, whatever they have at the time. So together with any electric charge, obviously there is electric current because whenever you are connecting negative, which has axis of electrons and positive, which has deficiency of electrons, electrons will fly, will flow, whatever, from one from the negative to the positive, positively charged object. Now what they could actually measure is the intensity of this flow. Because the more intense the flow is, the more other characteristics can be measured around it, in particular magnetic characteristics. We will definitely talk about all these things in details when we will basically talk about electromagnetic properties. But at the time they could measure these magnetically related effects and they could not measure the number of electrons or anything like that. So as the main unit, which they were using at that time, they were using the intensity of the current between negative and positive. And that they could actually measure by measuring the certain magnetic attraction between two conductors. And at that time they came up with the unit of intensity of the electric current called ampere. By the way, Coulomb is called and after the physicist by the name Coulomb and ampere is called after another physicist, which is called ampere. So in any case, the intensity of the electric current was at the time measured and could have been used as the unit. And then what they were actually saying is that the electricity electric charge can be measured as if you have a current of one ampere which exists during one second. So whatever the amount of electricity one ampere flow brings to another to the opposite conductor during one second is one Coulomb. So one Coulomb is one ampere times one second. So ampere was a primary unit and the second obvious is also a primary unit and the Coulomb was a derived unit. But then I think it was just in 2019 the International Committee, which is related to units of measurement CSI, System International Analy, they have actually decided to do it slightly differently. They have changed the definition of the Coulomb to this. This is the definition basically. Coulomb is such a measure of electric charge using which one electron has this particular charge expressed in Coulombs. So that's kind of a historical perspective and again right now if this is the definition it seems much more natural. So the definition of the unit of electric charge again, we started from just amount in one electron, which seems to be very natural, but then it's too small and they have just decided to proportionally increase it to something like 10 to the 19th degree. So our regular charges which we are dealing with can be expressed in like normal numbers, not such a huge one. So this is the story behind Coulombs. Now what I wanted to talk about this is just to give you some kind of feeling how big or how small Coulombs actually is. Well, it's quite big actually. I mean it's a it's rather big unit. So let's just start from the example which I was using during the previous lecture. Now in the previous lecture if you remember I was using two cubic centimeters of iron initially neutral, but then I said okay, let's consider that magically we took all electrons from here and transfer it there. All electrons which are in one cubic centimeter of iron. So one cubic centimeter. Well, it's a little bit smaller than this one, but it's really a small amount. So if we transfer all electrons and put these two pieces of iron on the distance of one meter and we were talking about how big attraction between these are. I just call that this is like huge. I mean these electrons which we are transferring from one object to another, now this becomes negative, this becomes positively charged and attraction, the force of attraction is so strong that it's comparable to the strength of the force between the Sun and the Mars. Now let me just use very very similar example to demonstrate something similar with number of coulombs in this particular charge. Now instead of cubic centimeter, I will take cubic millimeter which is really very very small cubic millimeter of iron and another cubic millimeter of iron and again I do exactly the same thing. I will transfer all electrons from one to another and I will put the distance between 100 meters. So two cubic millimeters of iron with all electrons magically transferred from one to another. So this becomes negative, this becomes positive. Now on a distance of 100 meter attraction between them will be of the same strengths about the same strengths as the weight of two Egyptian pyramids in Giza. So that's again huge. Now the question is how many coulombs are in this particular transfer. Now I was calculating basically based on the size one cubic millimeters weight and whatever else. So I use certain resources which I have on the internet. I found how many electrons are. So it's 2.2 by 10 to the 21st degree. That's how many electrons are in one cubic millimeters. So I transferred them there. Now this is negative, this is positive. Now what is it in coulombs? Well, I know that this actually is the number of electrons per coulomb and this is the charge of every electron in coulombs, right? So if I will use this and I will multiply it by the number of electrons I will have 2.2 times 1.6 and the 10 to 21 minus 19 so it will be approximately 3.5 times 10 to the second degree which is 350 coulombs. So 350 coulombs which is, well, I don't know, the number seems to be normal, right? No big deal. But if 350 coulombs, this is negative 350 coulombs, this is positive 350 coulombs. On the distance of 100 meters the attraction force is comparable to the weight of two Egyptian pyramids. Gravity, which is again huge. So as you see 350 coulombs is a very very big amount of electricity. If concentrated in one particular place, obviously. Now to have another kind of feeling about how much electricity goes from one place to another when we do have some kind of a conductor between two different charged positive and negative poles and here is what I can say as another example. If you take the regular incandescent lamp of 60 watt which is kind of average for many many lamps at home. And if you have regular American electricity supplied to the house, to the building, which is usually, let's say, 120 volts, and I'm not talking about what is volt. We will all be discussing this, but that's not the matter right now. What is a matter is that the current, electrical current, which is wattage divided by voltage, is 0.5 ampere. And as I was saying, ampere times one second is one coulomb. So in one second the amount of electricity going through the lamp is about, in one second, is about half of coulomb, right? One half of an ampere times one second. So every second half of a coulomb goes through the lamp. Now so how many seconds do I need to accumulate, for instance, this amount of electricity, which is basically a huge, as we know, right? Well, if it's half a coulomb then in one second, then we will have to have 700 seconds, right? So whatever, it's like 12 minutes or something like this In about 11-12 minutes, we will have amount of electricity which is going through the electric lamp of this type of wattage approximately equal to this really relatively huge amount of electricity, which we have purely artificially decided to calculate if we will strip all the electrons from cubicle millimeter of an iron and put it into another one. So whenever the charge, whenever the electrons are going through, they are going with a very, very intense flow, if you wish. And this is, you know, pretty substantial. So we are consuming a lot of electricity even in a simple incandescent lamp. Alright, so what's the bottom line of this lecture? I think I was quite surprised myself when I found out this historical perspective of how we measure electricity and something which seemed to be extremely natural to basically measure the amount of electric charge in number of electrons or any other proportionals unit, was not really how it was done from the historical perspective. And again, the reason is people did not know in the early days of electricity all these things which we know about atom, about electrons, about how to measure such things as number of electrons, for instance, etc. So these are all contemporary developments which led to a much more natural definition of the unit of electric charge, which is Coulomb. And again, what's very important is to understand that Coulomb is a rather big amount of electricity. And this is an example. These tiny one cubic millimeter, which is very very small of iron, if you will take all these electrons, it's about 350 Coulomb altogether. Okay, that's it for this particular lecture. The notes for the lecture contain a little bit more precise numbers about the amount of electricity in one Newton, in one electron, because there are actually like, I don't remember, eight or nine whatever digits after decimal point. But in any case, approximately, you can say that 1.6 times 10 to the minus 19s. Tiny, very tiny. Okay, so that's it for today. Thank you very much and good luck.