 Hi, I'm Zor. Welcome to Unizor Education. Today's lecture would be not very scientific. I'll just talk about certain usages of electricity and I will try to classify it somehow. Now, this lecture is part of the course called Physics for Teens presented on Unizor.com. So this website actually contains not only just individual videos, but it's a course. Physics for Teens is a course, which means there is a menu. The whole course is divided into parts, chapters, lectures, whatever. So I do recommend you to take the course and sequence it's presented. Also, there is a prerequisite course on the same website. It's called Math for Teens. Math is definitely needed for everything you do in physics and not only in physics, obviously. So the site is completely free. There are no any kind of financial strengths attached. There are no advertisements. So pure knowledge for your consumption. Okay, so let's talk about usages of electricity. So we're using electricity in certain devices and there are many, many different devices. So what I have decided is I'll break in two very large groups. I call them electric and electronic devices and the way how I can differentiate them is the following. Electric devices are those which use electricity to do some mechanical work or heating. By the way, when I'm saying heating, I actually include lighting as well because lighting in many cases is produced by heating. Not all cases, but in many cases. And that's exactly what I'm talking about. So it's heating and heating related lighting. So these are main purposes of devices which I call electric. And another group is electronic devices. Well, computers and stuff like this. Now, this will be a subject of a separate lecture. So today I will talk only about electric devices. So as I'm saying, and it's completely voluntary, I mean, obviously, I mean, some people might differentiate or classify devices differently. That's my choice. So today I'll talk about devices which are using electricity to produce mechanical work and heating. Okay, so I have a list of different examples of where exactly the mechanical work is performed by electricity. Now, the first device is obviously electric motor and we are using electric motors like everywhere. For example, I'll just read whatever I wrote. So water pumps, elevators, fans, compressors, in manufacturers' plans, all different devices are rotating like conveyor, for instance, or crane or something. All these devices are using collective motors. All drilling, washing machines. By the way, in case of washing machine, for instance, we are using electricity for two different purposes. One is to rotate the drum and another is to pump the water in and out. So it's one device and it's using two different kinds of motors, electric motors. So electric motors is a big deal. Now, as an example of the usage of electric motor in the water pump, I actually would like to do some calculations. So the calculation is what kind of motor I need to supply the water to the building where I live, for instance. So approximately, the data is as follows. We have 12 floors. Each floor, let's say, has three meters high, approximately. Now, I have 200 apartments and in the morning, during the three hours in the morning, let's say from 6 to 9, average usage is about 100 meters of water. And that's what I would like to supply to the building. Now, how do I supply it? Well, there is obviously the main which is coming from the street and there is a pump. Now, this pump is pumping the water onto the roof to the tank. There is a water tank on the top. And then from the water tank, it goes by the gravity. So all this water I have to lift to the roof first. I mean, that's the power which I'm supposed to supply. So let's just consider what is amount of work which is performed during this time, during first three hours in the morning. And then we can divide it by time and calculate the power. So what is the amount of work? I'm lifting certain amount of water. Now, what is amount of water? Well, it's 200 apartments, 100 liters each. So the amount of water will be 20,000 liters. Now, to lift it to 12th floor, each floor is 3 meters, so it's 36 meters high. So I have to lift 20,000 liters of water by the height of 36 meters. Now, the force which I have to basically apply to this is mass times g, right? Weight, basically weight or force is equal to mass times g, where g is 9.8 meters per second square, right? So mass times acceleration. So I have to lift the weight. This is the weight, basically. And the mass of a liter of water is 1 kilogram. So basically I have to f is equal to 20,000 times 9.8 newtons, right? Kilogram times meter by second square, that's newtons. So I have the force and I have the distance, 36 meters. I have to lift. So if I will multiply f times height, I will have work, which is equal to 20,000 times 9.8 times 36 meters. And this is equal to 7,056,000 joules. That's amount of work. Now, this amount of work is performed by times equal to 3 hours, which is 3 times 3600 seconds. If I divide my joules, work divided by time, that would be my power. So I have to divide 7 million something by this. And the result is 653 joules per second, which is 6053 watts. This is watts, okay? Joule per second. So this is the power, which is necessary to pump the water up to the roof. Now, what's obvious is that we have to really, first of all, we have to use a little bit more. I mean, sometimes you have some kind of a peak usage and abnormality or something like this. So approximately, if you would like to basically really calculate how it is in practice, you would probably decide 1,000 watts, which is 1 kilowatt. Motor you have to put in the pump. I mean, considering there are some powers which is lost in the motor itself, I mean, this is really a needed, pure needed power. Obviously, the motor should have more. Now, what's also important is that usually it's not such a good thing when motor is working all the time, like 3 hours pumping water without any interruption. So the way how it's usually done, they have a sensor in the water tank. If the water goes down below certain level, motor is turned on. And it should really pump very fast. So the motor should have more power than even this to exceed the consumption of the water. So whenever the power, whenever the level of the water in the tank is reaching certain maximum, motor should switch. So there are two sensors actually, on and off. Whenever it goes down and it's on to the motor, whenever it goes up, it's off to the motor. So that's how it's done, basically. Well, which means that motor should really be more powerful than whatever we are just thinking about. Well, let's say approximately 1.5 kilowatts. That would be probably a good idea. But then what happens if the motor breaks? We need an uninterrupted water supply to the building, like 200 apartments, 500 people. We can just wait until we will repair or replace the motor. So we need two motors. And they should really alternate. Whenever one breaks, another should really pick up completely its function. Now, while we have both motors, it's probably wise to reduce the load on every motor. And all the time, alternate them. So either one is working and then it's resting and then another motor is working. So we need some electronics, some switches to do this kind of a thing. So that's basically kind of the whole example of calculations people do when they have to design the buildings or something like this. Okay, so it's just an example. And out of curiosity, if you have a motor of this type of a power, what exactly is the amperage of the electricity, of the electric current which goes through it? If you have, let's say, 220 volts, if you have 200 volts, alternating current, and that way we're talking about alternating current in this particular case. So if you have P is equal to U times I, this is voltage and this is amperage. So if you have 220 volts and power is 1.5 kW, then I is equal to 1500 divided by 220, which is 6.8 amperes. So you have 6.8 amperes. Now, usually you have circuit breakers. They are calculated based on certain amperage. If the amperage exceeds some level, then they break. So usually in the apartment the breakers are on 10 or 20 amperes. 10 amperes for some smaller devices and 20 amperes for maybe electric stove, which really takes a lot of electricity. So basically this is kind of normal. It's below the circuit breakers limits, usual limits. Okay, that's all about electric devices which are making certain mechanical work and this is just an example of how mechanical work is calculated. Now let's talk about heaters. So heating is another usage of electric devices. Now of this example it is just a plain heater which heats the room or electric stove. Now something like a fan which we are using to dry the hair. It has two different functions. One is purely mechanical, so there is some kind of a fan which pushes the air through and then there is a heating element which is producing basically the heat and this flow of air is heated. What else do we have here? Well, obviously incandescent lamp. This is where we are using the heat to produce light. What else? Drying machine. Drying machine also has three different electric functions. One is purely mechanical when we are rotating the drum. Another is also mechanical, it's a fan because we are pumping the air in and the third one is heat related because the air is supposed to be hot in the drying machine. So that's also where the drying is used. And as an example, let's take a look for instance at incandescent lamp. Let's say it's 100 watts and 120 volts. So if you will take a look at the lamp, it's written on the lamp usually. The wattage and the voltage. Alright, so if this is true, what is... So this is the power consumption and this is the voltage. So the current is equal to P divided by V which is equal to what? 0.8333 Amperes. So that's the power. Sorry, that's the Amperage electric current. Now we can actually calculate the resistance of this lamp. The resistance, you remember the Ohm's law? So that would be 120 divided by this which is 144 Ohms. And now we can obviously check the formula that P is equal to U divided by R squared or I multiplied by R squared. You can just check, I mean it's all plain arithmetic here. So basically this is the Amperage which goes through 100 watts incandescent lamp with 120 voltage. You see, compare it with electric motor, 6.8 Amperes, right? This is 0.833, so it's significantly less, like 8 times less, right? Well, obviously, I mean the motor is doing real work. And this is, well, lamp, lamp is a lamp. Electric stove consumes significantly more because the heat in the electric stove is significant. And I think the Amperage goes to maybe 3, 4, 5 Amperes, something like this. Maybe more. It depends, obviously. And I also wanted to make another, just as an example of electricity used to produce heat. It's welding. You know what welding is when you're using electric arc between two electrodes. So if you have one electrodes and another, there is an electric arc between them. So electric arc has a very high temperature. So that's exactly how we're talking about, that's why we're talking about heating in this particular case. And it's so high that it melts the metal. So what you have is, you have to have a source of electricity, and the source of electricity is welding machine, obviously, which has electrodes which you connect the way how you would like to connect them to a proper place. And I've checked the parameters. What's interesting is that the current is very, very high. It's like a lightning, a small one. So this is the Amperage, 500 Amperes. Again, compare it to Amperage in the electric motor, 6.8 or something like this. You see, it's like 100 times more. So it's 100 times more intense flow of electrons through the arc. And that's why they're heating the metal so much that it melts. And the voltage produced by the machine is something like this. Which means that the power is 15,000 to 60,000 watts. So 15 kilowatts to 60 kilowatts. Depending on the machine, different machines, different usages. I mean, this is a lot. So that's basically what kind of interesting I think about welding. So the way how they do it, they first, they put together the contacts. And then when they just pull it a little bit, the arc still remains between them. And why it's really there? Because we have such a high power and it really breaks through the air. Electrons are going through the air. Usually, if not such a big power, then we don't do it. Air is really a good insulator. But in case the power is big, it goes through the air and forms an electric arc. Well, basically that's it. I mean, the whole lecture is just kind of an explanatory and exemplary. I just wanted you to be familiar with certain common devices. And in some cases, I did even some calculations just to familiarize with how the whole thing is working. This is an example of usage in electric devices. Next lecture will be about electronic devices. That might be a little bit more interesting because I will try to look inside the electronic device. With electronic devices, we know whether it is a stove or a fan or a drying machine. With electronic devices, it's much more interesting because I will try to really look inside. Okay, that's it for today. Thank you very much and good luck.