 So how do we explain what's happening inside these batteries, light bulbs and circuits when they light up? Well, to help you visualize what's going on, I have a simulation produced by the University of Colorado. In this simulation, we have the components that make up a simple circuit. We have a battery down the bottom here, then we have a light bulb, and we have a switch, and we have wires that are connecting each of these components. So the different components contain electrons, which are represented by these different blue dots that are along the wires and inside the circuit. At the moment, the components are represented by pictures. But by clicking the schematic option up here, now we can see the circuit diagram symbols instead. And this circuit clearly resembles the diagram drawn in the previous video. When the circuit is connected, the electrons start to move around the circuit. Let's have a look. So here, the battery is providing the energy that allows the electrons to move. When the electrons move through the light bulb, the energy they are carrying is turned into light energy, and this causes the light bulb to light up. Notice that it's not a single electron that moves straight from the battery to the light bulb to give it power. Instead, all the electrons move relatively slowly in the circuit. The speed at which the electrons move through the circuit is known as the drift velocity. The units of drift velocity are meters per second. Now, even though the electrons are moving slowly, if the battery is disconnected, so let's have a look at that now, the electrons stop flowing almost instantly, and the light stops. Let's have another look. Notice that the electrons do not build up anywhere in the circuit. If one electron moves, it pushes all the other electrons along. So the electrons remain evenly spaced, and they do not build up or become spread out. Also notice the battery does not create any charges, and the light does not destroy the electrons or use them up. Instead, light is just produced as the electrons travel through the light globe. Before we move on, I quickly wanted to talk about the energy in this circuit. It takes energy to move electrons through a light bulb. It resists their movement. However, the electrons do not slow down as they move through the light bulb. Electrons are not losing kinetic energy as they pass through the light bulb. Instead, the battery provides the energy to keep the electrons moving. So imagine that the light bulb is a gear, and the electrons are a chain. The battery is doing work to pull the chain and make the gear move. Or in this case, the battery is doing the work to pull the electrons around the circuit and make the light bulb shine. Although the electrons are carrying the energy, they do not slow down or lose kinetic energy as they move.