[Music] hi and welcome back to freiz lessons. co.uk by the end of this video you should be able to describe what's meant by a battery you should then be able to calculate the potential difference produced by a battery now over the last few videos we've been looking at current and potential difference in both series and parallel circuits all of the circuits we've seen so far have contained a cell and here's the symbol for a cell now in physics we often use the word battery so let's take a look at what that means a battery is simply two or more cells connected together and I'm showing you the symbol for a battery here now there is one key point about batteries the cells and a battery must be connected in the same direction so as you can see in this battery the positive ends of the two cells are both pointing to the left so in this video we're looking at how to calculate the potential difference produced by batteries here's a single cell with a potential difference of 9 volts so what would happen if we connected two of these cells in series like this to form a battery well if we measure the potential difference using a voltmeter we can see that it's two * 9 volts in other words 18 Vols so the potential difference of cells adds up to give us a total potential difference of the battery here's one for you to try each cell has a potential difference of 9 volt determine the overall potential difference of the battery pause the video and try this yourself okay so in this battery we've got three cells and each one has a potential difference of 9 volts multiplying 9 by three means that we've got a total potential difference of 27 volts here's another one for you again each cell has a potential difference of 9 volts I'd like you to determine the overall potential difference of this battery so pause the video and try this yourself okay putting a voltmeter across this battery tells us that we've actually got a potential difference of 0 volts we can explain that by looking at the direction of the cells the left hand cell is pointing in the correct Direction with a positive end on the left however the right hand cell is pointing in the wrong direction this means that the potential differences of these cells cancel out so the battery has an overall potential difference of zero okay here's a final question for for you again each cell has a potential difference of 9 volts I'd like you to determine the overall potential difference of this battery pause the video and try this yourself okay so in this battery we've got three cells two of them are pointing in the correct direction and here they are the potential difference from these two cells will be 2 * 9 Vol which is 18 Vols however we can also see that this cell is pointing in the wrong direction this will cancel out one of the other cells so the overall potential difference of this battery is 9 volts in total remember you'll find plenty more questions on determining the potential difference of batteries in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to describe what's meant by a battery you should then be able to calculate the potential difference produced by a [Music] battery