Alright, guys. So now we're going to start talking about capacitors and capacitance. These are common objects that we'll see in electricity, and we'll definitely need them when we start getting to circuits. You'll need to know what they are and how they work, so let's go ahead and take a look. So imagine that I had these two charges. We talked about how positive and negative charges, if you have them some distance apart, basically have some energy between them. So in other words, this positive and negative charge, which by the way we called an electric dipole, the fact that these two charges are positioned some distance apart, they have some electrical potential energy between them. And basically, what happens is that a capacitor is instead of just having one charge and one charge, we now just have a sheet or a surface of charges in which all of these charges are positive, so we have a positive q. And then we have another surface that has negative charges built up on it, so we have negative q. And now, what happens is that the fact that these plates or these surfaces are some distance apart, so we have some distance right here, these carry a lot more potential energy between them. And this is basically what a capacitor is. A capacitor is 2 surfaces of equal and opposite charges, and the fact that these are equal and opposite basically serves to store potential energy between them. It stores a lot of potential energy because none of these charges are actually moving.
Okay? So how do you get these charges to get on these plates or these surfaces in the first place? Well, to do that, you have to connect this capacitor to a battery. And in doing so, you produce what's called a simple circuit. We have a diagram of a simple circuit right over here. But basically, and we're going to talk a lot about circuits in later videos, but these circuits are basically just conducting wires, which are the black lines. And these conducting wires just mean that charges can easily flow between them. And so it's these conducting wires and some other stuff, which we'll talk about later. So, you have this capacitor that is hooked up to a battery. So all of these charges that basically build up on the surfaces of this capacitor, the source of those moving charges comes from potential differences. So we know that any charge that as it moves through a potential difference is going to gain or lose some energy. Now, this potential difference, the best example, is commonly called a battery. So what a battery is And by the way, this is just the standard symbol for a battery. It doesn't actually look like this. This is just what we've chosen. Now, the standard setup for a battery is that the longer end right here, the longer terminal is usually what we call the positive terminal. This is just something that physicists have decided for a 100 years ago that this is just going to be the way it is. So the longer terminal is going to be the positive. The shorter one is going to be the negative. And by convention, because we didn't actually know how electrons move back then, what specific direction, we just chose that electrons were going to move in this direction. This is just that we chose. It's not going to affect the physics in any way, but you're just going to have to get used to it. So the electrons will start moving this direction right here. So we have the direction of motion of these electrons, and what ends up happening is they start building up on the surfaces of these capacitors. You're going to have a whole bunch of negative charges that start building up over here as the electrons are flowing through the circuit. Now what happens is that these like charges will want to repel, and the opposite charges will want to attract. So that means that on the other side of the capacitor, the electrons will keep on going. They'll basically flow upwards here because now they have some potential, and you have the positive charges that will start building up on the other side of the capacitor. Now, so basically what happens is I'm just going to start making up some numbers here. Imagine that we had a 4-volt potential over here and a negative 4-volt potential on this side of the battery. What ends up happening is that these electrons will start to move. They'll start to set up these surfaces of charges right here. And basically, all of this will happen until the potential on this side of the plate is equal to negative 4 volts, and the potential over here is positive 4 volts. Now what happens is essentially the potential differences between the battery and the capacitor are always going to equal when you have a situation where you have 1 battery and just be let's see just be Let's see. Final minus initial. So if these electrons are moving towards this side right here, we're just going to pretend that they do, the potential difference would be final, which is the negative 4, minus initial, which is the positive 4. So, in other words, this v would just be negative 8 volts. So that we have the potential difference that these electrons experience. Now, as they move across the capacitor, now what happens is the potential difference over here, Δvof the capacitor is going to be 4minusnegative4. So that means that this voltage is going to be positive 8volts. So now we can see that the voltage of the battery in this circuit here, Δvb and the voltage of the capacitor are basically going to equal each other. Now that's basically a really, really important part. Now as for the charge that builds up, we can actua...
