 Hi, I'm Zor. Welcome to Unisor Education. We continue talking about electricity and its properties. So today we will talk about very important property of electricity, the way how electricity is converted into heat and basically some quantitative relationships between the heat and electricity. Now this lecture is part of the course called Physics for Teens, presented on Unisor.com. So I suggested to which this lecture from the website because every lecture has very detailed notes. It's like a textbook and all the lectures are organized in certain segments. It's a course basically. Also in the same website you can find the prerequisite course called Math for Teens. Lots of mathematics is used in physics, especially in my course. So I do suggest you to be very comfortable with math, especially with calculus and vectors. Okay, so let's talk about heat. Well, as many other things in physics, certain laws are discovered first experimentally and then later on some theorists come up with explanation. This is no exception. There was actually a certain number of experiments which were conducted back in the 19th century, usually associated with two names, Joel and Lance. These two physicists were experimenting with electricity and certain aspects of properties, of certain environments the electric current was actually going through. As a result, they came up with very interesting property that certain amount of energy is released when the electric current is actually going across something, some conductor. And this amount of energy which is released is basically the heat and they measure the heat. And they found basically a couple of very interesting things that for instance, if you measure the electric current and electric current, they could actually measure using certain tools which they have. So it will be proportional to square of the electric current. Also, it was proportional to square of the voltage if electric current is constant. And the proportionality to electric current is with voltage constant. And also, what was important, the greater the resistance is with the same current, the greater amount of heat is released. So it's proportional to resistance. Now, if we are having the current constant and both current and voltage constant and depend only on resistance, then again, it will be depending on resistance. So let me just do some kind of theoretical calculations here to basically explain all these experimental facts. And let me start from definitions of all these characteristics of electricity which we know of. We know of voltage, we know of amperage and we know of resistance. So these three characteristics actually are very important and they define the circuit. So what is the circuit? Consider a very simple one. So you have the source of electricity of direct current and you have, the only thing you have is a resistor. That's it. So you know the difference in electric potential between the terminals of the source, which is the voltage. R is the resistance. Now voltage is measured in volts, resistance is measured in ohms and the electric current is measured in amperes and we have the ohms law, which is what u is equal to i times r. So we will use this ohms law for certain theoretical and logical conclusions. So let's start with the definition. What is a difference in electric potential, which is one volt? Now by definition, it's if to transfer one cologne from one terminal to another, if it requires one joule of work, then we are saying that the difference between electrical potential is equal to one volt. So voltage of one volt means that it requires one joule of work to move one cologne of electricity from one terminal to another. Now let's go with another definition. What is the amperes? One amper. One amper is the measure of the electric current when one cologne of electricity is moved across the wire during each second. Now let's consider our situation. If we have the voltage u, now if voltage is one volt, we know it requires one joule to move one cologne from one terminal to another. If voltage is u volt, to move one cologne of electricity requires obviously u joules, right? So to move one cologne of electricity between the terminals with u voltage requires u joules, right? One volt, one joule. U volts, u joules. That's basically the consequence of the definition of the voltage. It's all from the definition. Okay, now, so we have u joules to require to move one cologne. Now how many colognes do we move each second? Well, if our amperage is i, again one amper is one cologne per second. Amperage i means i colognes per second. So if u joules require to move one cologne then i colognes per second requires u times i joules. And this is per second. And finally, if you have this particular circuit in operation for a certain time, like t seconds, the amount of work is equal to u times i times t joules. Okay? So again, let me repeat this logic. If one joule requires to move one cologne in case the voltage is one volt, then u joules required to move the same one cologne if the difference of potential voltage is u volts. Now if one cologne requires one joule to move between these terminals, then we need i colognes per second to move, which means we need u times i joules per second. And then if you have it for a t seconds, you have this particular formula. Now, so this is the formula for amount of work. The source of electricity is actually performing to move electrons. Now we know it's electrons because in the 19th century they had no idea about electrons, right? So they were just adjusting to whatever they had to. They knew that electricity is something and they were able to measure the voltage, the amperage. As a result, they were measuring the resistance, etc. But they didn't know about electrons. So all they were saying is, well, there is something heat produced, but they didn't know why. Now we know that right now this is the work which is performed by the source of energy and it moves electrons around basically. That's what it does. Well, obviously there is a result of this. So what's the result of it? Assuming in this course and in probably many other cases that the wiring doesn't really resist the electrons. Well, there is a resistance, but we're a small one relative to this. Or if you wish, you can say that, okay, all the resistance which is in both wires and some kind of detail, whatever it is here, is all together as R. It doesn't really matter. So what I'm saying is that the result of electrons moving, now, the energy is supposed to be conserved. So if my source of electricity is exhausting certain energy, does work. It's supposed to be some kind of, it's supposed to result in something. So what's the result? Energy doesn't disappear. So if we spend some work, something must be done. So what is being done? Well, when the electrons are moving, if this is a resistance, what they're doing? They're pushing around actually all the atoms as they are moving along the circuit. And as a result, all this chaotic movement of the atoms inside whatever the thing is made of is basically a heat. Because what is the heat? Heat is an intensity of the moving of the molecules inside the object. So as electrons are moving, they are excited the atoms a little bit more. And the more intense movement, well, what is intense movement of electrons? That's the current, right? So the more intense the current, the greater this excitement of atoms inside this particular object is. So the temperature is rising. So the result of this energy spent to move the electrons around is a more intense, chaotic movement. And therefore, heat, the rise of the temperature of the resistor. Now, this particular formula can be slightly modified using the Ohm's law. So it's the same as if you will substitute instead of I, you will substitute IR. Instead of you substitute IR, you will have I squared RT. So this is a good formula when your current is constant. Now, if your voltage is constant, then you better use I is equal to U over R. So it's U squared divided by R. So these are different formulas which gives you amount of work and therefore amount of heat. Not in calories but in joules, but they are actually the same measurements of the amount of energy. So it's just different scales. But in any case, this is amount of work which is performed by this particular source of electricity. Now, is it good or bad? Well, for instance, if you will consider incandescent lamp, why does it light up? Well, that's why. Because the electricity which is going through the lamp heats up this tungsten spiral inside the lamp. And when the temperature is rising, well, obviously it heats up. But you know that when the temperature is rising, first the metal becomes red and then it will be white basically. And it will emit certain amount of energy as a heat and as a light basically. It's a radiation of energy. And that's how we light up our rooms. Now, in some other cases, let's say it's a computer circuit. Well, the electricity going through all these circuits and obviously heat up all the details, which quite frankly is not good for electronics. So we're trying to cool down. Now we cool down by doing what? Well, first obviously we can put some kind of a cooling mechanism like going, circulating the air inside. And that's why we have certain fans inside the computers. Well, the progress in technology actually resulted in changing the voltage of the entire circuit. And you change the voltage. Obviously you decrease the amount of heat which is basically emitted by all these circuits. So that's another way to fight this particular thing. So sometimes heat can be good, sometimes heat can be bad. But in any case, it's always related to electricity. In practical cases, for example, obviously all the wiring which we have, it has certain resistance. And since it has certain resistance, it produces certain heat. And in many cases that's not really a desirable thing. We're trying to reduce the resistance. And if we reduce the resistance, then obviously we will have less heat emitted. Now let's just think about it what happens. If you reduce the resistance, if you is constant and you reduce the resistance, you will increase the I. Right? Now, how does it affect the amount of heat which is actually emitted? Well, you can use one of these formulas obviously. And I will have a few problems in the next lecture to calculate what exactly is amount of heat. What happens if we, for instance, in the same circuit, we will put instead of one particular resistor, two resistors of the same thing, what happens with current, what happens with amount of heat which is emitted. So these will be little problems which we will solve in the next lecture. So far, I do suggest you to read the notes for this particular lecture on unizor.com and try to perform all these little calculations which I had. And what's important is repeat the logic, what exactly leads to this particular formula. It's very useful to understand basically the theoretical concept behind this. That's it. Thank you very much. Good luck.