before we look at exactly how transformers work let's very quickly recap how they're used in the national grid most of our electricity here in the uk is generated at huge power stations which are spread out all across the country once they've generated the electricity it has to be passed through step up transformers which increase the voltage to around 400 000 volts the purpose of this is to minimize energy losses as the electricity is sent across the country in a huge network of wires and pylons then once it gets to where it needs to go like a small town it passes through a step down transformer which decreases the voltage to around 230 volts so that it's safe to use in our houses so to sum up the role of a transformer is to increase or decrease the voltage of electricity to see how they do this let's take a look at a single transformer the grey stuff is a chunk of iron which we call an iron core and it connects the primary coil on the left to the secondary coil on the right now how they work is kind of confusing at first and in the exam you're gonna have to be able to use the correct terms properly or you won't get the marks so just bear with me as i explain it but you might have to rewatch this bit a couple of times the way we're going to approach it is to consider what happens to each part of the transformer step by step the first thing to happen is that an alternating potential difference is applied across the primary coil which causes a current to flow and generates a magnetic field around the coil because the potential difference is alternating though the direction of the current and thus the magnetic field will also alternate next this alternating magnetic field in the primary coil induces an alternating magnetic field in the iron core because remember iron is a magnetic material so it can become magnetized if it's exposed to a magnetic field lastly the iron cores magnetic field induces a potential difference across the secondary coil and if it's part of a complete circuit which it will be in a transformer then this causes current to flow around that secondary coil so to summarize all of this the transformer is effectively just transferring the current from the primary coil over to the secondary coil but instead of the electricity just conducting straight across it uses these induced magnetic fields and the reason it can't just pass straight across is because the wires are insulated in plastic so the electricity can't pass between the wire and the iron core now the reason that we have to use all of this weird magnetic stuff is because it allows us to change the size of the potential difference for example in this one which is a step up transformer if we put a 10 volt supply in we'll get a 20 volt supply out this is because there are twice as many turns in the secondary coil as there are in the primary coil so our voltage gets doubled in contrast this transformer will step the voltage down because there are fewer turns on the secondary coil than there are on the first anyway that's everything for this video so hope that all made sense and i'll see you again soon you