[Music] hi it's Mr Anderson and today I'm going to be talking about voltage current and resistance all of these things are found in electric circuits it's hard to see electricity move and so lots of times we don't have a gut instinct for what what's really going on and so I always like to start with an analogy um the analogy here is going to be the analogy of water and so if we have a bunch of water at the top of a water tower it has potential energy and potential energy in electricity is going to be called voltage and we measure that in volts um as that water flows down to a toilet or a sink the current and the symbol for that is I the current is going to be how much of that water is actually flowing and so the water's going to flow down and eventually through the sinks in the toilet it's hopefully going to be cleaned and then eventually pumped back up to the top of that water tower again and so what's resistant we call that R resistance is simply um anything that resists the flow of that electricity and so anything like smaller pipes or um maybe clogging inside the pipes that slow down the passage of the water is going to offer resistance likewise anything in a wire or anything that slows down electricity is going to offer resistance and so voltage is measured in volts current is measured in amps and resistance is measured in ohms and each of those terms comes from a famous scientist that figured some things out about electricity now today I'm going to use What's called the circuit construction kit um if you want to play around with this you could go to this website it's called P.C colorado.edu and they put together a wonderful simulation that shows you how electricity actually works and so it's a circuit construction kit the one that I'm using is a DC that means direct current construction kit and so what you can do is you can add a battery so let's a battery and if you control click on it or right click on it you can actually show the value and so this is a 9vt um battery so that means it has that much potential energy and so the batteries that you put in a fire detector it would be an example of a 9vt um let's add a wire to that and another wire and let's measure the current that flows through it and so I'm going to put an ammeter out here let grab that and this is going to measure the amps which is going to be the current that flows through it let's also grab another wire and let's kind of make this a complete circuit so if I grab a wire here another wire here and then we connect it back up okay so if we add a I wire over here as well now if you know anything about electricity you know that something bad is about to happen uh I'm about to short this battery so what happens to a battery when it's shorted out well you can see that the electrons are just cruising around you see the ammeter is off the off of the um it's pegged all the way to the top it's also says that it's reduce the animation to less than 1% of its normal speed and so uh in the lab that's bad because you'll get Sparks and you also could explode your battery so let's not do that I'm going to split this Junction right here uh and actually let me split it right here so um that's bad or that's a not a healthy circuit and so now let's add the third thing so again what we have is we have voltage that's the potential energy we have current that's the flow of the electrons but now let's add a resistor here so if we add a resistor to our to our circuit and then connect it up and let it run then we have a healthier looking circuit and so what we now H have is potential energy that's pushing the electrons in this direction it's going through an ammeter which is measuring the amps as it moves through it and now we have a resistor and that's something that's slowing down the passage of those electrons and let's actually show that value okay so what do we have let's get back to our terms again we've got voltage or V and we can see that that's a 9vt battery we have amperage and so that's going to be current and we use I to explain what current is or that's the symbol for current uh we measure that in amps and then the last thing we have is resistance and resistance is going to be measured in ohms and so we can actually look at these values vales and you should be able to figure out what's called ohms law so we have 9 volts we have 10 ohms of resistance and we have 9 amps and so if you take 9 9 equals uh 10 sorry about the bad writing times9 in other words we could start just with the numbers itself and so Ohm's law is simply this V equals itimes R whoa that's an ugly looking R so V equals I * R in other words the voltage equals the current times the resistance and so what should happen if we increase the voltage well if we increase the voltage and the resistance is set so it's not going to change if we increase inre the voltage what should happen to the current well let's try it so if I do that if I increase the voltage excuse me so let's change the voltage let's now change it to um a higher value what's going to in happen to the amps or the current the current is going to increase the resistance stays the same and so as I increase the voltage what's going to happen to the current the current's going to increase and the cool thing about this animation is watch if we increase the voltage even yet it shows the electrons it tries to represent the electrons in their speed and so the more volts that we add to our battery the more current we get moving through it now likewise what happens if we change the amount of resistance so now let's change the resistance so it's a 10 ohms let's increase it let's say we increase it let's say we make it 51 MMS what happens to it well as we increase the resistance then the current is going to decrease and so there's an inverse Rel relationship between the resistance and the current and then there's a direct relationship between the voltage and the current and so that's going to be simple uh that's simply going to be ohms law and so you can solve problems in other words if I were to close this up let's close this up not show you what it is if I didn't know what the voltage was but I knew that the current was .94 amps and I knew that the resistance was 51.2 ohms we should be able to figure out the voltage and so in a simple circuit um you can figure out based on current based on Resistance and volt you can figure out one of the other ones um the best way that I remember this and so you may use a different kind of a a pneumonic to remember this is I have this pyramid where I have voltage at the top I have current on one side and resistance on the other and so all I do is simply use my hand and I cover up the one that I want to find and so let's say my unknown is voltage I could simply cover up the V and that's going to be the um current times the resistance and so if I don't know the voltage so if I cover that up voltage is simply going to be the current times the resistance um if I don't know the current so let's cover that up let's say I don't know the current current is going to be the voltage divided by the resistance and likewise if I don't know the resistance if I cover that up uh resistance is going to be the voltage divided by the current and so this whole thing is called ohms law and this is bad writing um not too good at the Mouse um so this would be ohms law and it just shows us the relationship between voltage current and resistance um and all of these are named after famous scientists that worked on electricity um this would be Volta so the volts come from uh Volta this is be resistance and so this is uh ohms and then current is amp uh ampere is his name and so um that's 's law and the easiest way to figure out um how each of these things work is to actually use the circuit construction kit um you can also use things like this we can use a voltmeter so we could put a voltmeter right here and you can actually put the voltmeter in different places and it'll me measure the voltage and so that voltage would be 4812 um and so you can use an ammeter and then let me get rid of that for a second if you really want to have fun uh then you add something called a light bulb so if we add a light bulb to this again we have to have electricity flow in One Direction and in the other we can actually generate light and so if I change the resistance so let's change the resistance so let's get a variable resistor I can decrease the amount of resistance and we get greater current so we have electrons that are flowing at a greater rate and we also have more light and we have more heat and uh that's a simple circuit I'll talk more about what is a parallel circuit what is a series circuit uh a little bit later but I hope that's a great start