 In this video we're going to investigate voltage, look at its units and have a look at a formula for voltage. So voltage is represented by the symbol capital V and the way I understand it is to look at the units. So the units of voltage is volts which is the same thing as joules per Coulomb. So a volt means an amount of energy per charge. How many joules of energy per charge or Coulomb of charge? So to help us understand voltage let's go back to the diagram that we had before of potential energy in a circuit. So the voltage at a particular point in a circuit is equal to the amount of energy a charge would have if it was at that particular point. So for example if I had a charge and it was at this point in the circuit there down below and I put that on my diagram it's about there. If I have a charge at that particular point it would have high potential energy and so it has a high voltage. Whereas if I had a charge on the other side so here and that would correspond to an energy of about there then this would have a low potential energy and so that amount of potential energy per charge is volts. So it would actually have exactly the same shape. This graph would have the same shape whether it was potential energy on the y-axis or volts on the y-axis. So I'm going to put that one in now. So it doesn't matter if I could put this as potential energy or as volts which is joules per Coulomb and the graph would still have exactly the same shape. Now normally in a circuit we don't want to know the voltage at a particular point. Instead what we care about is the change in voltage across two points or the potential difference. So in this particular case the potential difference between this point here and our other point up here would be equal to the size of that gap in there. So potential difference means difference in voltage between two points in the circuit. And this would tell us the difference in voltage between this point here and this point here. So if potential energy and voltage look the same on this diagram that can be represented by the same curve why do we use voltage? Why don't we just use potential energy? Well as time goes on and charge carriers move from the positive terminal of the battery to the negative terminal the amount of potential energy in the battery is going to decrease. The potential energy is being converted into light so the remaining potential will decrease with time. However both the brightness of the light bulb and the voltage across the circuit will remain the same unless the battery starts to get very flat in which case the light bulb will dim and eventually go out. But this is why we use voltage rather than potential energy. Voltage allows us to easily make calculations and predictions about the behaviour in a circuit like for example the brightness of a light. So we're going to look at this more in an upcoming video. For now I'm going to show you a formula that you can use to calculate the voltage. The formula is V equals W on Q where V is the voltage and that's measured in volts. W is the work or the energy delivered to the electrical component and Q is the charge that has flown through that component. So this is a formula that you can use to calculate voltage. Have a go at this now.