now when it comes to current there are two types that you need to know about alternating current which you often write as ac and direct current or dc in an alternating current the direction of the current is constantly swapping back and forth so the charge flows in one direction then the other direction and back again we get these alternating currents whenever we use an alternating potential difference or alternating voltage so one that fluctuates between positive and negative we can see this if we measure the potential difference or current over time they constantly fluctuate between negative and positive and at the circuit level this means that the direction in which the charge is flowing will constantly be swapping back and forth here in the uk all main supply electricity which is the electricity that comes from our plug sockets and powers our computers and kettles and so on is ac and specifically uk main supply is 50 hertz and around 240 volts which means that on our bottom graph the potential difference fluctuates from positive 240 volts to negative 240 volts and back again 50 times every second and so the current will also fluctuate at that same rate one thing we should mention is that you'll sometimes hear that the voltage is 230 volts rather than 240. basically it can be either in the uk so they're both correct as far as your exams are concerned direct current on the other hand is produced by a direct potential difference which is either positive or negative the entire time so the charge is always flowing in the same direction we find direct current in things like cells and batteries like those in your phone or a calculator the last thing we need to cover is that in order to get these potential difference first time graphs we use devices called oscilloscopes which display the graphs on a monitor anyway that's everything for today so hope you found the video helpful if you did then do share with your friends and we'll see you next time