in this video we're going to take a look at what circuits are and how we can draw them with a couple simple components we'll also explore the terms potential difference current and resistance before finally seeing which way around a circuit current flows an electrical circuit is just a closed loop that contains a power source such as a cell and something for the electrons to flow through like this wire we generally represent them with circuit diagrams and this here is probably the simplest type of circuit you'll see in order to draw more complex circuits we need
to know these symbols for the different components and where to place them there's a whole bunch of symbols that you need to know and i'll cover them all in more detail in other videos for now though we'll just consider the main ones we've already seen a symbol for a cell which is basically just a simple version of a battery as batteries are made up of two or more cells their symbol is just two cell symbols put together although as far as exams are concerned cells and batteries both act in the same way another common symbol
is for the filament lamp which is just a small light bulb so if we added one to our circuit and turned on the battery then it would light up we could also add a switch which could be closed allowing current to continue flowing around the circuit or open which would disrupt our circuit and so turn off our light in order to explain what's going on we need to look at some key terms specifically potential difference current and resistance current denoted by the letter i is a measure of the flow of electrons around the circuit similar
to the flow of water through a pipe and it's measured in amperes which are often just called amps and are denoted with the letter a meanwhile a potential difference denoted by v is the force driving this flow of electrons and is provided by the cell law battery you can think of this as the pump that forces the water along the pipe another name for potential difference is voltage and it's measured in volts finally resistance r is exactly what the name suggests it's everything that resists or opposes the flow of electrons similar to a partial blockage
in our pipe example and it's measured in ohms the last thing we need to cover is which way around the circuit current flows if you look at the cell on this circuit diagram you can see that it has one longer line and one shorter line the longer line in a cell or battery is always the positive terminal whereas the shorter line is always a negative terminal now because electrons are negatively charged they flow around the circuit from the negative terminal to the positive terminal however when people first discovered electricity they didn't know anything about this
so they decided that current flows from positive to negative and we now keep this convention sometimes calling it conventional current so even though it's a bit weird just remember that for your exams current always flows from the positive terminal to the negative terminal that's everything for today though so hope you found it useful and we'll see you next time
