Electric current

Added: 2026-05-15

[00:00:02]now for our basic definition of electric current and electric current is defined uh as the amount of charge moving past a particular point in a circuit per unit time we can write that in an equation of course so it's just the charge divided by the time it takes for that charge to pass that point and sometimes it's written um without the Delta symbols so it's just the charge passing per unit time the units of of current are looking at that equation what are they they're the units of charge which isums divided by the units of time which is seconds so kums per second or we call uh amps as the um other units or ampi or a as the symbol so in this example um a typical laptop uh requires about a a current flow so 8 amps to charge up so how many electrons per second is this well we know that the current is the amount of charge passing every unit time so if we rearrange this equation to find out how much charge there is we can say that for a current of 8 amps in 1 second that is 8s of charge now we know that one electron has a charge of 1.6 by 10 -9 not right about the sign right at this moment because this is an absolute magnitude of charge that we've calculated over here so the number of electrons is the total charge divided by the charge per electron which gives us a hell of a lot of electrons it is five by 10 19 electrons which are traveling every second this is per second we put in one second over here this is 5 by 10 19 electrons moving through the charging device every second so we know that electric current is the rate of movement of charge so let's have a really schematic diagram of what uh the charges looks like look like inside a wire and this is not really what it looks like of course electrons are very very small um compared to the size of the yre but if we placed a negatively charg we placed an electric field across this y here so we've made negative charges over here and positive charges over here the charges inside that y would experience a force sometimes it's known as an electromotive Force it's a push all of them feel the same Force almost like a parallel in the case of parallel plate they're all feeling the same force in the same direction and so we look at all those charges we feel the same Force they're all going to move in that direction at about the same rate so that that potential difference that you apply across a wire which is the basis of circuits um is transferred simultaneously to every single charge in that wire so so here's a little interactive demonstration suppose you got you at this yre again and each negative sign represents one electron of course it's much more complex than this which we'll discover in subsequent videos but if we do this we can calculate the current in electrons per second and then convert it to amp so what we've got here is our our reference point going to see how many charges pass that point in a certain amount of time and here's our clock all right let's see if we can do this I'll count the electrons and try and stop when that gets that uh Point gets back to the beginning 1 2 3 4 5 6 7 8 I think it's about eight uh electrons pass every cycle so let's say we've got eight electrons passing every three let's make it 60 seconds let's pretend that was a minute so our charge is 8 electrons times the charge on an electron which is 1.6 by 10-19 so that's do it a little more straightforwardly which equals 1.28 by 10 the -8 kums the time it took let's say it was a minute 30 60 seconds worth and so if we combine that into our current we can say it's the charge divided by the time which is 2.13 by 10us 20 or let's let's round that to 2 by 10us 20 since we don't know those values very precisely obviously it's not a particularly realistic example um but there you go you can go through a calculation in that manner