[Music] Good day grade eight learners and welcome back to tumamina teaching. My name is Lunal and I will guide you through this lesson of electrical systems and we'll specifically focus on circuits. This will be your second lessons of five lessons of natural science in term three. We have a lot of work to cover. So let's get started. So what is electricity? Electricity is a form of energy. The kind we use in our homes, in schools, and our phones is called current electricity. Current electricity is the flow of an electric charge. That is usually made up of tiny particles called electrons through a conductor like copper wire. Electric charges can move or flow when there's a complete path to follow. This path is called a circuit. Sometimes an electric charge can jump across a gap causing a spark or a shock. A basic circuit has four main parts. The first part is conducting wires which is made of metal that conduct or carry the electric current. A cell or a battery which stores chemical energy and converts it into electrical energy. An output device like a bulb or buzzer that changes the electrical energy into another form like light, sound or heat. And lastly, a switch, which controls the flow of electricity. When it's on or closed, the current flows. When off or open, the flow stops. So, grade a without even one of these main parts, the system won't work. The cell changes the chemical energy in the battery to electrical energy in the circuit which flows through the wires as an electrical current. The bulb then changes the electrical energy into light and heat energy. This is how energy is transferred in an electrical system from chemical to electrical light or heat energy. When you switch on a television, the circuit connects to the main power. Electrical charges flow through the wires into the TV. The electrical energy is changed into light, heat, and sound energy. That's why your TV lights up, gets warm, and makes sound all at the same time. All appliances work this way. Whether it's a fan, a kettle, a speaker, they operate by completing a circuit using the transferred energy. A circuit is a pathway that allows electricity to flow. In a closed circuit, electrons flow from the negative terminal of a cell to the positive terminal through the external circuit. Electrons which carry electric current in most circuits flow from the negative terminal to the positive terminal externally. But a conventional current which is used in diagrams and circuit symbols flows from positive to negative. So why the difference in the flow of electricity? Let me explain. Electron flows works as follows. Electrons are negatively charged in a circuit. They are repelled by the negative terminal of the cell or battery and attracted by the positive terminal. So electrons flow from negative to positive through the wires in the external circuit. So this is what actually happens in real physical terms. Now your conventional current works as follows. This is a historic model from the 1700s before electrons were discovered. Scientists originally thought electricity flowed from positive to negative. So they drew diagrams and made rules based on that. Even though we know now electrons go the other way, we still use conventional current direction positive to negative in circuit diagrams, textbooks, and calculations. So think of it like this. Just as map is not the real world, but it helps you navigate, so is the conventional current, a useful model to help you understand how electricity behaves even if the maps or in this case the diagram doesn't show the electrons moving in the right way. So to recap, when this circuit is closed, electricity can flow. If there's a gap or the switch is off, it becomes an open circuit and no current flows until something closes that circuit. We see electric circuits every day in torches, remotes, and even in doorbells. Some circuits have a resistor which is a part or also known as a component that reduces or limits the flow of a current. So why do we need a resistor? You can pause this video and quickly discuss it in class. [Music] While some devices can get damaged if too much electricity flows through them, it is especially helpful when there is load shedding. Oh no. Great. I know we all know what load shedding is. Load shedding is a controlled and scheduled process where electricity supply is intentionally turned off in certain areas for specific periods of time. This is done when the demand for electricity exceeds the available supply to prevent the entire power grid from collapsing. It is important to know how each of these are measured in a circuit. The current inside a circuit is measured in amps. The batteries voltage is measured in volts, which is the potential power of the circuit. The resistor's resistance is measured in ohms. and watts measure the power that is actually used in a circuit. A resistor acts like a traffic officer. It keeps the current at a safe level. You'll often find it in radios, TVs, and even in fairy lights. So, let's test it. I will hand over to my colleague at Stalen High School, teacher Noel Slabbert, to explain to you the electric current and the use of a resistor. Over to you Noel. Welcome to the lab. My name is Noel Slober and we are here at the laboratory um at Wor Salamos and today we will just be looking at the effect that a resistor has on the flow of the current in a very simple electrical circuit. So I have a basic circuit here in front of me. Firstly, we need two 1.5 vol batteries. We need a few wires that you can see already have been connected here. We need a very simple light bulb which we call a torch light bulb. And then later we're going to add in our resistor. So first we're going to build a very simple closed circuit even before we put in the resistor. So, I've built my circuit so far. It just isn't closed yet because this pole of the battery hasn't been connected to the circuit. But when I enter and it connects, you can see that our light bulb shines nice and brightly because the circuit is now closed all the way through. The pathway is closed through the batteries. So, let's just change this circuit slightly. I'm going to add in our resistor. So, I'm going to take out one of the wires. Now, the current is not flowing anymore. So, I'm adding the resistor into our current at this moment. So, you can see that the light bulb is much dimmer than before. That's because the resistor is reducing the amount of current flowing through the circuit. Less current means less energy reaches the bulb. So it shines with less intensity. In science, we use symbols to represent circuit components. This makes diagrams easy to draw and understand. Let's look at the most common ones. Wires are straight lines that connect the components. A resistor slows down the flow of a current. A bulb is represented as a circle with a cross. A cell is a source of electrical energy and the battery is two or more cells connected together. An open switch is a break in the circuit and the current stops. And a closed switch is a complete path and the current flows. And lastly, a buzzer gives off a sound. It looks like a half circle on two legs. We use these circuit components to draw a circuit diagram. That is a scientific drawing that shows how components are connected in a circuit using symbols and straight lines. So, let's practice. Use the symbols you see on the screen to draw your own diagram. Your teacher will pause this video to give you time to do so. In three, two, one, let's go. [Music] Great job on drawing a detailed diagram. Maybe your drawing looks something like this. If not, here are other options. [Music] And just like that, we have reached the end of this lesson. Next time we will dive into electrical currents, which is part of electrical systems. If you want to test your knowledge, follow the link in the description below to do the self marking quiz. And remember, if you like this video, please subscribe to the channel. See you soon. Bye.