[Music] hi and welcome back to freci lessons. co.uk by the end of this video you should be able to explain what's meant by potential difference you should then be able to describe how we can measure potential difference and finally you should be able to describe potential difference in series circuits so far we've had a good look at electric current and you should remember that electric current is simply a flow of electrons around a circle so in this circuit the electrons move out of the cell make their way through the wire pass through the lamp and then return back to the cell now the lamp lights up and that's because the electrons are giving the lamp energy so let's take a look at the energy transfers involved the cell has a store of chemical energy this is transferred to electrical energy and that's carried by the electrons passing out of the cell when the electrons pass through the components such as the lamp the electrical energy is then transferred to other forms of energy in the case of a lum this is light energy and thermal energy so energy is transferred an electrical circuit we can explain this using the idea of potential difference this is also called voltage and you can use either expression in the exams a potential difference of one volt tells us that one Jewel of energy is transferred for each coolum of charge that's moving through the circuit we measure potential difference using a voltmeter I'm showing the symbol for a voltmeter here and it's important that you learn this so here's a simple electric circuit and I'm going to measure the potential difference of the cell using a voltmeter to do that I place the voltmeter across the cell like this in this case the voltmeter is giving us a reading of 9 volts this is telling us that the electrons are transferring N9 Jews of energy per Kum of charge now we can also use a voltmeter to measure the potential difference across the lamp and I'm doing that here the potential difference across the lamp is also 9 Vol so can you see that all of the electrical energy carried by the electric current is transferred to light energy and thermal energy in the lamp Okay so I hope you're getting the idea that potential difference is actually fairly straightforward it simply tells us how energy is transferred in an electrical circuit okay this shows a circuit with two lumps in series we're going to explore the potential difference in circuits like this as you can see the potential difference across the cell is still 9 Vols this tells us that the total energy transfer in this circuit is the same as the last circuit now one key feature of this circuit is that both lamps are now dimmer than the single lamp in the previous circuit we can explain this by measuring the potential difference across the lamps like this this tells us that the potential difference across each lump is 4.5 Vols so you you can see that the total energy carried by the current has now been shared between the two lumps and that explains why both lumps are dimmer than when we only had one lump if I've only got one lamp then all of the energy carried by the current is transferred to that one lamp so it's bright but when I've got two lamps in series the energy is shared between the lamps so they're each dimmer now in this circuit I've made the two lumps identical but they don't have to be in this circuit I've got two different lamps this lump has a potential difference of 6 volts whereas this one has a potential difference of 3 volts but the key point is that the total potential difference across both lamps is the same as the potential difference across the cell so to recap the cell has a potential difference of 9 volts which means that 9 Jew of energy are transferred for every coolum of charge this energy is shared between the two lamps the the lamp with a potential difference of 6 Vols will be brighter as it's transferring more energy than the lamp with a potential difference of 3 volts remember you'll find plenty of questions on potential difference in series circuits in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to explain what's meant by potential difference you should then be able to describe how we can measure potential difference and finally you should be able to describe potential difference in series circuits [Music]