hello grade 10 and welcome back to another video with me Miss Martins in today's video we're going to be looking at electricity or electric circuits and this is a summary video of the entire section now with that being said this is an overview I don't do a lot of past paper practice in here but I have that Linked In the description box below but this goes through basically everything that you need to know for your exam I go through formulas definitions Concepts important Theory and how to do certain calculations so I hope that you stick with me throughout the entire video because I give loads of teacher tips along the way um as a teacher that sets marks moderates exams I can help you level up your marks remember to subscribe for more physics chemistry and math let's jump right into the video this is basically an overview of what you need to know for electricity or electric circuit you need to know your variables and units know your formula know when to use which formula you need to be able to draw circuits both series parallel resistor connections and a combination of both you need to understand the listed Concepts and you need to understand how to work with series circuits parallel circuits and once again a combination of both so that's what this video is going to be going over very briefly remember it is a summary so for a more indepth look at circuits you need to look out the links in the description box below but you should know that electricity is the movement of charge the flow of electrons and that is what creat creates electricity it's the flow of charge mostly electrons we have a battery or source of electrical energy that is connected with conducting wires like copper wires resistors or other electrical components so for example we can want to power an appliance so we can have a battery or a power source connected with conducting wires we have a light bulb that we want to power we have a microwave that we want to power and electricity and the section is all about energy conversions so we start off with chemical potential energy within the battery and that is converted to electrical energy okay so electrical energy is what causes the charges the electrons to move around the circuit and that electrical energy is converted into heat energy or light energy or energy needed to power the appliances so you need to understand this flow of energy and how it's converted or transformed remember energy cannot be created or destroyed just transformed from one form to another so this is the flow of energy it is very very important to know that we need a closed circuit in order for electric current to flow or in order for our charges to flow cannot be an open circuit our switch must be closed and you'll often see a discussion surrounding the direction of current flow so this says although moving charge in most metal conductors are electrons electrons are negative and think about that if they're Negative they will flow from the negative terminal of the battery to the positive terminal that's what makes sense that's called electron flow current that's the blue circuit I drew over here so because electrons are negative they flow from the negative terminal of the battery through to the positive terminal because negatives are attracted to the positive that makes sense it's called electron flow current but we work with conventional current flow which is current flow from the positive terminal of the battery through to the negative and just as a reminder a battery can be represented by the following symbol like that the small line is the negative terminal of the battery the big line is the positive terminal of the battery so just know the differences between conventional currents and electron flow currents we work with conventional current okay so as I mentioned we need a closed circuit in order for electricity to flow in order for current to flow the conducting wires usually copper provide a pathway for the current to flow and the push comes from the battery that's my energy source or my power source now it is very important for you to be able to draw a circuit and to be able to look at a circuit and understand what the different components are so I've listed some components that you will be seeing in circuits and it is important to understand the symbols so a cell looks like this as I've shown you the long line is positive the small line is negative this is representative of a battery with three cells so what they could say to you is that the voltage across the battery is 6 volts and if I have three cells that means that each battery will have an EMF of 2 volts or each cell sorry so 2 volts 2 volts 2 volts together it gives me 6 volts you need to understand that this is an open switch and a closed switch remember switch must be closed in order for the current to flow in the circuit to function this is how we draw a light bulb there are more than one ways there's more than one ways often to represent light bulb or resistor this is generally what we use so a light bulb looks like that a circle with a cross in it then we've got a normal resistor you will either see a resistor represented with a squiggly line like that but more commonly in our curriculum it looks like this like a little box okay that's a resistor a rat is a variable resistor so we can change the resistance of a r stats an ammeter measures current and it's always connected in series a voltmeter measures potential difference or voltage and it is always connected in parallel I will show you what that means in a second this basically just goes through the different components so battery consists of multiple cells I speak here about the energy conversions which we've already been through conducting wires or metal wires often copper and they attach to the terminals of the battery they allow the flow of current then they speak about resistors so this is a resistor a light bulb is also technically a resistor a light bulb or a lamp we've got rats as mentioned it has an arrow through it to show that it's a rear stat and meters are connected in series so here we can see this is the main line of the circuit the ameter is connected in series so it's connected along the main line of the circuit you can see that a voltmeter is different here's the main line of the circuit there's the main line of the circuit the total current flows through that main line the voltmeter branches off which means it is connected in parallel and the reason why voltmeters are connected in parallel is because they have a very very very high resistance which means that current does not want to flow through them what this means is that if I decided to connect the voltmeter in series like this so if pretend that instead of the ameter we have a voltmeter if I had to connect a volt meter in series the total resistance of the circuit would be way too high which means current would be tiny and the circuit would not function so we connect it in parallel like this because the current does not want to flow through here all that this voltmeter does is it measures the potential difference between two points in a circuit so for example tells me the voltage or the potential difference across this resistor or this voltmeter over here would tell me the potential difference or voltage across the battery the current does not want to flow through there right now before I show you the difference between resistors connected and parallel and series I want to go over the different variables within an electric circuit and grade 10 11s and 12s this is so so so important I Mark papers all the way up to metric level and I often see that students get confused between the quantity okay and the symbol to represent that quantity and the unit there's a massive massive difference so I've made a table summarizing what that difference is I've listed all the different um quantities that you will see throughout electricity or electric C the symbol and the unit and I've given an example of how we use it so starting from the top of the table we've got potential difference or voltage the symbol for that is V and the unit for that is V so for example if I want to say the potential difference across the battery is 10 volt I say the potential difference across the battery is equal to 10 Vols this is the symbol it's basically a placeholder instead of writing potential difference or instead of writing voltage okay I explain it over here like if I say my height is 155 CM instead of writing my height is 155 CM I can say h is equal to 155 CM so H is a symbol it's like a shortened version of writing out height but the unit is cm is okay so the unit always comes after your answer it is very very very different to the symbol and Learners often get this confused in the context of current so if I want to say the current the total current in the circuit is 3 amp instead of writing current is equal to 3 amp amp is the unit instead of writing the current is equal to 3 amp I can write I is equal to 3 amp I is a symbol for current okay cool now while I'm speaking about symbols and units and stuff like that it is very important to note that you must write a as your unit for current not amps I know some teachers some textbooks some YouTube videos May informally refer to a as being amps that's incorrect we actually Mark that wrong so if you say three amps we're going to take away your answer mark because amps is an incorrect unit you either write a or you write out the full word ampers I know that that might sound silly um but and a little bit pedantic but that is how we Mark okay then we've got resistance is measured in ohms that's the symbol for ohms you say ohms charge the symbol is q and it's measured in kums C is kums the charge is 10 kums work or energy they mean the same thing so work done or energy transferred is measured in Jewel J power p is measured in what what okay those are my symbols for my quantities and those are my units it's very important to know those then in grade 10 this is the formula sheet that you receive in your exams now in grade 11 and in grade 12 you add we add a lot more formulas especially those relating to or energy and relating to power however these are my basic formula and you need to know this whether you're in grade 10 11 or grade 12 so let's quickly go over what these formulas are these formulas are to calculate resistance within a circuit if my resistors are connected in series I use this formula R1 plus R2 plus whatever if I have three resistors then my formula needs to include R1 R2 and R3 if I have two resistors in series my formula will stop over there I hope that makes sense this is for series resistors then if resistors are connected in parallel which I will go over in a little bit in this video we use 1 / RP is 1 R1 + 1 R2 if I just have two resistors in parallel you stop over there you don't have to put the dots if I have three resistors in parallel it goes 1/ R3 so those are my formulas in order to calculate resistance and remember resistance is measured in ohms this formula over here is used in order to calculate charge okay so the amount of charge transferred in a circuit charge is measured in kums or we can use this formula to help us calculate current remember current is measured in ampi and then this is time and this is very important to note but in this formula time must be in seconds it's often given in minutes we need to convert this formula is used to calculate potential difference or voltage very very important please take note that potential difference and voltage it means the same thing I know we often refer to it as voltage you know informally but potential difference is a more correct term it's measured in volts W is work done or energy transferred remember although the formula says W as in work work done they can also give it to you in terms of energy work and energy are the same thing it's measured in Jews we spoke about q q is charge measured in kums this formula over here is representative of what we call ohms law you may see it represented in a triangle like this v i r is obviously resistance it's measured in ohms V is potential difference or voltage measured in volts and I is current measured in amp you need need to know when to use which formula and in order to know that you need to understand your quantities or your variables a massive part of completing electricity and circuit questions is knowing and being able to recognize when our circuits and our resistors or our components are connected in series versus when they are connected in parallel or when there's a combination going on so resistors in series I have highlighted this already but I'll show you once more if I start by the battery and this is supposed to be a battery and I follow the main line of the circuit so you take your highlighter or you take your finger and you follow the main line of the circuit like this you can see that R1 R2 and R3 are all connected in the same line the main line of the circuit there are no branches which means R1 R2 and R3 are connected in series in order to calculate the total resistance of the circuit you will say R1 plus R2 plus R3 three you will simply add them up 10 + 20 + 30 and that is equal to 60 ohms that's how you calculate resistance resistance in series super easy same thing with this um circuit they're all connected in series and same thing with the circuit over here they're both connected in series as you can see it doesn't matter if I draw R1 and R2 next to each other or R1 over here and R2 over here they're still in the main line of the circuit therefore they are connected in series a parallel connection is quite obvious to see this and this over here is representative of the same circuit the reason I drew both of them is because in some exams in some textbooks and some study guides you will see it being represented like this in some um books you'll see it being represented like this and some P papers but they mean the same thing so in yellow I've highlighted where the total current will be in the circuit so from the battery total current total current total current total current total current and then at this point over here which I will indicate with a red dot we can see that there's a split in the main line of the circuit some of the current goes through the top Branch so in other words through R1 and some of the current goes through the bottom bran through R2 then they join again so this will still be R1 over here on this side over here this will still be R2 over there and then once again at the Red Dot they join and it becomes total current again this is the same thing except the branching is just drawn a bit differently so it splits there and there R1 R2 this is basically the same representation total current total current total current then there's a split some of the current goes through this Branch the 15 ohms and the rest of the current goes through the 7 ohm Branch like this and then they join up again at this point over here and these circuits over here represent the same thing it's just that over here there are three resistors in parallel now how would you calculate resistance in parallel I mean if I had to do the circuit over here at the bottom because it actually has values what I would do is I would say 1 / RP because these are in parallel 1 / R1 + 1/ R2 R1 and I want you to think of R1 as being this Broad brch what is the resistance of this Branch this branch is 15 ohms so it's 1 15 plus R2 I want you to think of R2 as being this branch which resistors are in that Branch just the 7 ohms so it's 1 over 7 then what you do is you type it as is on your calculator like that 1 15 + 1 7 it's a bit of a terrible number but you get 22 over 105 but please and I will do this again in a later question take note that let me write it a bit nicer this is 1 over RP is 22 over 105 I just typed 1 15 + 1 7 on my calculator I do not want 1 over RP I'm looking for RP resistance and parallel so what I need to do is I need to flip this fraction so take the reciprocal or flip this fraction because I'm flipping this fraction I need to do the same thing to the other fraction so it's going to be 105 over 22 and you can work that out on your calculator 105 over 22 and I get RP as being 47 7 ohms okay so you flip this fraction flip this fraction and then work out an answer remember write it to at least two decimal places and there's my unit now here are some other cir circuits and I hope that you can recognize that this is a combination these circuits are combination circuits in other words we have a resistor that is in series and we have resistors that are in parallel I know that these circuits look a little bit different to what you're used to seeing maybe in textbooks study guides or in past papers they come from the internet but it's basically the same thing let's see this is the battery so you see it says 12 Vols this is where your battery would be connected so let's just draw a battery with two cells this is the main line of the circuit so the total current will flow you see it says it total current the total current will flow through R1 okay then I hope you can see that there's a split in the circuit there I've got a branch and some of the currents will go through this Branch the rest of the current will go through this branch and then they meet up again at this point and then the total current once again will flow through this part of the circuit so everywhere where you see yellow is total current and then where you see the green that's a split current and then the blue that's the rest of the current what does this mean this means that these two resistors are in parallel and this resistor is in series so how would I work out the total resistance of this circuit well I want you to always start off with any parallel resistors always start off with a parallel combination and as we discussed this resistor over here the 12 ohm and this resistor over here the other 12 ohm they are in parallel and the way that we know that is because some of the current goes through this Branch the green one and some of the current goes through the blue branch so they are in parallel there's a split in the circuit so what we need to do in order to calculate resistance of the circuits I'm going to write your resistance or total resistance how we do that is we start off with the parallel resistance so we're going to go 1 over RP now how many branches do I have I have the green branch and the blue branch so 1/ R1 plus 1 / R2 I want you to think of R1 as being the green branch and I want you to think of R2 as being the blue branch that's my formula you get a mark for writing your blank formula then what is in the green Branch what resistance is in the green branch this one 12 ohms so it's 1 over 12 plus what resistance is in the blue branch look at the blue branch we've just got this one 12 ohms so 1 over 12 basically you can do that on your calculator but this is a very easy one this is 2 over 12 and remember what I showed you we don't want RP we 1 / RP we want RP so we must flip that fraction so RP comes to the top it's basically RP over one if we flip it but RP and then we flip this fraction fraction as well so it's going to be 12/ 2 what's 12 2 it is 6 ohms now what you need to understand about this is what this means is that sure when the current splits some of it goes through this 12 ohm some of it goes through this 12 ohm overall this part of the circuit has a resistance of 6 ohms so it's kind of like removing the parallel section and replacing it with something that has six ohms will basically be the same as the situation that I have at the moment where I have two 12 ohms in parallel I hope that makes sense so overall this part of the circuit is 6 ohms but remember I also have this resistor over here in series this 6 ohms so therefore my total resistance is this resistor this 6 ohms so the one I'm going to call it the yellow one the one that I've highlighted in yellow plus this 6 ohms the one that I got over over there so my total resistance is 12 ohms so you first work out the parallel get an answer and then add any resistors that are still in series let's take a look at one more circuit and this one can be quite confusing um and it's this one here on the right so if I have this is my battery okay there's my battery once more the total current will flow through the battery the total current will flow through this 6 ohm over here and the total current will flow through here but then I have a split in my circuit there's the split and there's the split depending on which way you look some of the current will go through this Branch over here the rest of the current will go through this Branch over here so how do I work out the total resistance of this circuit I changed the values of these resistances just to keep a little bit interesting a little bit different let's make this one 10 ohms I just don't want the same answer as the previous one and let's make this one 4 Ohms so what we do first is we work out the parallel resistance and now I want you to remember what I told you in the previous example I want you to think of 1 / R1 1 over R2 I want you to think of each of these as a branch okay I want you to think of each of them as a branch so the green branch is going to be R1 and I know that that's confusing because you're like wait ma'am isn't R1 a resistor so shouldn't there be two of them I want you to think of these things as branches this is where a lot of my students go wrong if they when they don't think of it like this think of the blue branch this one as R2 okay so the a wrong formula wrong formula would be saying 1 / RP is 1 / R1 1 / r2+ 1 / R3 and I know some of my students think that because they there's 1 2 three resistors here however you will only use a formula like this if there are three branches so you'll only use one of R1 one of R2 and one of R3 for a circuit that looks like this one where there's one two three branches if we only have two branches like we do in this example the green branch and the blue branch we only have one of R1 and one of R2 so R1 is is both of these resistors together four and two together why am I adding them like this because the four and the two are sitting next to each other they're in series so it's 1 over 4 + 2 basically it's 1 over 6 because this branch has a resistance of six plus the blue branch 1 over 10 so it's 1/ 6+ 1/ 10 I want you to use your calculator to do that you don't need to do it manually and we get four over 15 but remember we must flip both fractions so RP is 15 over 4 Ohms if you want to write that as a decimal you can um so 15 over 4 is 3A 75 ohms now what we just calculated is the resistance of the parallel connection so this thing basically has a resistance of 3A 75 ohms but remember we are looking for the total resistance of the circuits so we must still add this resistor in series so the total resistance is 3A 75 which is basically resistance in parallel plus 4 Ohms which is basically my resistance in series and we get 7 comma 75 ohms so once more you work out the parallel then you add what you have in series so if there were two in series say there was another 4 Ohms then you would say 3 75 + 4 + 4 but we only have one in series we don't have that one so that's why it's just plus 4 I hope that makes sense let's move on understanding series versus parallel circuits and what happens to current and what happens to voltage Within These circuits is very very important so on the screen you can see a summary of that and the two most important things to remember is that in a series circuit current is the same everywhere every everywhere throughout the circuit but voltage splits in parallel the opposite is true so the current splits and voltage is the same for resistors connected and parallel so if we compare these two circuits over here let's look at the series circuit first what it means is do you see that the ammeter over here measures 1.5 amp now remember we said in series current is the same everywhere in the circuit what that means is the total current is 1.5 amp so 1.5 amp will flow through the battery 1.5 aamp will th flow through the ammeter 1.5 amp will flow through the 2 ohm resistor the reading on A2 the reading on this ameter is 1.5 amp 1.5 amp flows through the 4 ohm resistor 1.5 amp flows through here and back to the battery there are no splits in this circuit there are no resistors connected and parallel so current is the same throughout so that is what it means by current is the same however voltage splits so what that means and I really really want you to understand this carefully what that means is the voltage across the battery you can see here it says 9 volts so what that means is if I had to connect a voltmeter across the battery like this remember voltmeter reads potential differential voltage if I had to connect a voltmeter across that battery it would read 9 volts now that 9 volts is the total voltage total potential difference or external or terminal potential difference okay terminal potential difference and that 9 volts is split amongst the different uh resistors or components in series so sum of the 9 volts will go here and the rest will go here we can actually work out how much voltage will go to this resistor I hope you remember the formula V is equal to I * R remember I is current the total current well the Y the total current flows through this resistor so 1.5 amp 1.5 amp flows through that resistor and the resistance is 2 ohms so that means that the voltage V1 is 3 Vols so what that means is that when V1 has a reading V1 will read 3 volts if I had to do a similar calculation but for this resistor over here it will be v = i * R current 1 small is 1.5 remember the total current 1.5 flow through both of these resistors times the resistance over here is 4 and 1.5 * 4 is 6 Vols so this volt meter over here will read 6 Vols and I hope you can already see what's happening if I take 3 Vols plus 6 Vols it gives me 9 volts and that just shows me that voltage in series is split just what it says there so of the 9 volts across the battery 3 Vols goes here 6 Vols goes here 3 + 6 is 9 Vols let's look at the parallel circuit parallel circuit is the opposite current split splits in the parallel circuit so what that means is if we look at the parallel circuit the total current will flow here because these parts are in series the split has not happened yet so this would be total current total current as soon as you get to a split as you can see here the circuit line splits as soon as you get here if you go this way the the circuit line splits sum of the current goes through here as I've mentioned previously in this video and sum of the current goes through here so current splits in parallel current splits however voltage is the same and what that means is if you take a look at the circuit we have no resistors connected in series here we have the 1.5 ohms and this 1.5 ohms connected in parallel and what that means is the voltage across this 1.5 ohms is the same as the voltage across this 1.5 ohms and in this case th those voltages will be the same as the voltage across the battery because they're all in parallel so the battery if I had to attach a voltmeter across the battery it would read 9 volts because it's says 9 volts over there that means that V2 would read 9 Vols that means that V1 would read 9 volts that is because n parallel voltage is the same across parallel resistors so here's basically a summary of what I just mentioned okay for current and here's a summary of what I mentioned for voltage so how we could represent this mathematically for parallel is the voltage across the battery 9 volts is equal to V1 which is equal to V2 they're all equal to 9 for the series circuit the voltage across the battery which is 9 volts is equal to this voltage plus that voltage but what about when I have a circuit that looks mixed like that and when I say mixed what I mean is I have parallel resistors over here so the 8 ohms and the 8 ohms are in parallel but we also have another 8 ohms over here that's in series so hard works is as follows the total current will flow through this part of the circuit so A1 will read total current the total current will flow through the resistor in series then when I see a split in the circuit over here we know that the current will split some of the current will go through the top branch and the rest of the current will go through the bottom branch and then they join again over here and then the total current will flow through this part of course this will only happen when the switch is closed so just bear that in mind so that is what happens with current and I hope that you can be aware of the fact that so A1 will read total current it'll read total current A2 will read a split current A3 will read a split current but what this means is if I had to take this current the current reading on A2 and the current reading on A3 and I had to add them together it would give me the total current so basically the reading on A1 is equal to A2 plus A3 so the current the total current is equal to the current in the top Branch so the current in the green Branch let's say plus the current in the blue branch I hope that makes sense so current splits as soon as we have resistors that are connected in parallel for the voltage what happens is quite interesting and what happens is the following you can see that we have V1 over here so V1 measures the total voltage or total potential difference or terminal potential difference like we like to call it so V1 basically reads the total voltage or potential difference now remember voltage splits in series now now what that means is that you see we have this resistor over here in series and then we have what we call the parallel connection now I need you to understand that let's pretend I'm just making up numbers over here well I see here V1 is 24 volts we can probably work out the the actual amounts here I'm not bothered by actual amounts I'm just going to use make U make believe amounts just to illustrate this concept so say V1 reads 24 Vols then if V E2 has to get let's pretend it is 10 Vols that means that the parallel combination will get the rest so it will get 14 volts I hope that makes sense because the total voltage V1 is split between V2 and V3 so V2 is 10 Vol V3 is 14 14 + 10 get you 24 remember I just made up these amounts and now you might be saying okay um I'm I'm not really sure if I understand ma'am because these are in parallel so what does that mean doesn't that mean that they get the same voltage so wouldn't it be seven and seven no remember how I want you to think of it is as follows think of it as this 8 ohm is connected in series Almost with this parallel connection okay so the green part of the circuit is connected in series with the blue part of the circuit and we know that voltage splits in series so this part of the circuit gets 10 volts this part of the circuit which is the parallel part gets 14 volts and what do we know about voltage in parallel if we go back to our summary that I showed you over here voltage is the same in parallel so all that means is that if the voltage across the parallel connection is 14 volts it means that the voltage across this 8 ohm resistor is 14 V and the voltage across this 8 Ohm resistor is 14 Vol okay so 14 over all over here plus 10 gives me the 24 and understanding that is actually really really important for answering circuit calculations now let's jump into using some of the formula now what I've basically done is I've copied and pasted important definitions that you may see in your textbook in your um exam guidelines and such so we've got EMF which is going to come into play in grade 11 and 12 more but I want us to focus on all of these as being definitions for voltage potential difference okay and I want you to see the following I showed you this formula earlier in the video but look at how it connects to our definition the potential difference across the ends of a conductor is the energy transferred and remember we said energy transferred is the same thing as work done okay okay so energy and work is the same thing so it's the energy transferred per unit electric charge flowing through it now if you take a look at that in words so the definition and you look at my formula they match so potential difference is V there's V potential difference is equal to energy transferred remember W is the same thing as energy transferred it's work done or energy transferred so it's equal to the energy transferred per per when you see per I want you to think of divide per unit electric charge and Q we know is charge so again look at the formula look at the words they match so potential difference is equal to the energy transferred all the work done per which means divide unit electric charge and it matches with our formula so this is a very basic example of how you can get asked to use this formula they say 2 kums of charge so Q is equal to 2 kums remember kums it must be in kums not nanocs or micrum but it is in transfers 6 jewles of energy remember energy and work is the same thing so work or energy doesn't matter is equal to 6 Jew what is the potential difference across the resistor so we're looking for V so we looking for V we've got Q we've got e or w so we use the following formula we looking for potential difference the energy transferred or work done is 6 Jew and Q is the charge it's 2 kums so that means that the voltage or the potential difference is 3 Vols another thing that I just want to show you about this formula and they ask this sometimes in multiple choice is we know that the unit for V for potential difference or for voltage U voltage is volts right volts or V an alternative unit however is as follows what do we measure work in or energy it's measured in Jews per this this is a per line over here means divide what's the unit for Q charge we got Jewels divided by charge Jewels divided by charge if you take charge to the top of the fraction remember this has got an exponent of one if we bring that to the top it's Jews per Kum so volts the unit volt is the same as the unit Jews per Kum just a little side note because you can get asked that in a multiple choice question so that's how we would make use of that formula remember let's speak about current our next Formula so the flow of charge is current we know current flows through a circuit as soon as the switch is closed current flows and here's a little bit of a summary slide for current so there's the definition current is defined as the rate of flow of charge and something that I need you to know for physics in general and chemistry is that when you see rates when you see the word rates I want you to think of dividing by time dividing by time current is defined as the rate of flow of charge so it's charge divided by time that is current and that's where this formula comes from look at formula current so current is I current is defined as the rate rate means dividing by time see we dividing by time the rate of flow of charge so charge divided by time there we go and just like we did with the previous situation we know that the unit for current is amp so for example 3 amp however if you take a look at the the formula so current let's do it on the slide quickly current is the rate of flow of charge so it's charge divided by time what is my unit for charge kums what is my unit for time seconds so it could also be represented like that which is a very rare way to represent the unit we represent it as amps but just be aware that they can ask you questions like that so a type of question that you can get asked to use this formula would look like this calculate the current so we're looking for I that passes through a lamp so a lamp is like my resistor if 30 C 30 kums okay that is my charge 30 Kum so charge is 30 kums current is what I'm looking for and 5 Seconds is my time my change in time is 5 seconds so the formula that I use is current is equal to charge divided by time rate of flow of charge the T / 5 which is 6 amp that is exactly how we use that formula take a look at a different type of question that we can get asked a current of 0.45 amp so they're giving me I flows through a light bop for 1 hour this is obviously time but time is given in hours yeah it must be given in seconds how do we convert hours to seconds I hope you know that you need to go from hours to minutes which is time 60 and then minutes to seconds which is time 60 again so to go from hours to seconds you times by 3,600 okay they want charge so once again you write your formula you substitute in your value so current is 0.45 that was given time is 3,600 because it was 1 * 60 * 60 or 1 * 3,00 600 that's how I got it from hours to seconds and then you say 045 * 3,600 and there's my answer with my unit the last formula that we need to speak about is this formula over here and this is known as ohms law okay ohms law is something that you touch on in a lot more detail in grade 11 but for now I just want you to be familiar with the formula for ohms law which looks like this you can also see it in a triangle over here another thing that you can be asked in grade 10 is to understand the factors that affect resistance and these are the factors that affect resistance I will go through this in a separate video but you can learn this off by heart because it can pop up in your exam and I want to quickly show you how these things are related in the relationship this is the formula that you need to be familiar with and I just want to discuss something that I hope is obvious the total current so I'm going to say the total current in this circuit is 4.5 amp which means that 4.5 the total current will flow through here as soon as we get to a split in the circuit the current will split now one thing that I do want to ask you is remember resistance is the opposition to the flow of current and I hope you understand that that means if you have a high resistance it's difficult for current to flow so think about high resistance difficult for you to get through high resistance okay so if I have two resistors I have two resistors connected in parallel a 6 ohm and a 6 ohm here and a 3 ohm over here the 6 ohm has a bigger resistance I'm going to write your bigger resistance and what that means is it's more difficult to flow through through this resistor so remember the total current will flow where you see blue then the current will split some of the current will go through the 3 ohm the rest of the current will go through the 6 ohm they split but the split is not equal the reason they don't split evenly is because the resistors are different remember 6 ohms has a bigger resistance which means it's more difficult for current to flow so what that means is because it's more difficult for current to flow through the 6 ohms there will be less current traveling through the 6 Ohm resistor for the 3 Ohm resistor it's a smaller resistance which means more current I hope that makes sense if you have a smaller resistance so you're not really resisting it's easy to flow if you're a current imagine your current you see three you're like Ah that's not bad 3 ohms easy to flow through there more current will go through the yellow Branch when the currency is a 6 ohms they think oh goodness that's a very big resistance it's very difficult to flow through the 6 ohm because it's bigger so I'm going to avoid going through there so less current will go through there okay and I want you to always also realize that this relationship is true because the voltage across them are the same so remember we said the voltage across the battery is 9 Vol which means the voltage across the 3 ohms is 9 volts and the voltage across the 6 ohms is 9 volts so what that means is the voltage is the same same voltage constant voltage and because that's the case if I have a big resistor big resistance I'm going to have a small current so just remember that the relationship between current and resistance is called inversely proportional okay and inversely proportional relationships that is true so current and resistance are inversely proportional if voltage is constant which it is because they're in parallel in this case that means that if you have a big resistance you have a small current if you have a small resistance you have a big current and that is one thing that you absolutely need to know in grade 10 we go into this in more detail in grade 11 you can look at these slides so long if you are interested so there's a slide there's a slide and I do mention that it is more grade 11 work but I do want you to understand this this concept if you're in grade 10 you do need to understand that and based off of that concept I'm going to show you how we split current when resistors are in parallel so I actually want to start off with a basic example which is one that I showed you already earlier in this video and it looks like this remember it was this example okay so I am going to make up values for this just to make it a bit easier let's pretend that the total current flowing through the circuit is 4 amp and remember what that means is total current if that's 4 amp it will flow everywhere where I'm highlighting it in purple or pinkish color so 4 amps will flow through all of that as soon as it reaches this point it's going to split that means some of the current will go through the top Branch the rest of the current will go through the bottom Branch this one over here right now how does the current split in this case it is super super easy because the yellow branch do you see the yellow Branch the top branch has a resistance of 8 ohms see it just as that resistor 8 ohms and the green branch has a resistor of 8 ohms it means that the resistances is the same because the resistances is the same the current split will be the same which means that the four ampers will split equally what that means is two amp of current will go through the yellow branch and two amps of current will go through the green Branch 2 + 2 is 4 easy stuff so the only reason that the current splits equally is because the resistance of the top branch is equal to the resistance of the bottom branch and that is exactly what I wrote here for you so you can take that down as a note if that helps you um remember it however in this example over here I hope that you can see that the two resistors in parallel so they're not the same um what I've shown you on the screen over here I hope this doesn't confuse anyone is a snapshot of a circuit so imagine it's like a little piece of a circuit like this so I've basically just chopped off the piece of the circuit so the total current is 6 amp and it flows through the circuit like that so 6 amp is the total current and the total current continues there and once it reaches here the current splits so it's just basically what I've done is I've taken a snapshot of a circuit the parallel resistors that's all I've done so don't get confused so total current is 6 amp it flows and then it stops some of the current will flow through the top Branch some of the current will flow through the bottom Branch but it's not going to be 3 amp and 3 amp I know 3 + 3 is 6 but are these resistors the same no this is 5 ohms and that's 10 ohms so you should know from what we've discussed which resistor should get more current remember the smaller the resistance the bigger the current so if R is is very small current is going to be big so because 5 ohms is smaller than 10 ohms 5 ohms will get more current Okay small resistance big current and what do you notice about the ratio of these resistances it's a 1 to2 ratio I'll show you that in a second but what I mean is this R this resistor is double the size of R1 which means that R1 should get double the current of R2 okay because the resistance is half the current should be double they do the opposite remember they're inversely proportional I'm going to show you an easy way to do this even if it is a little bit confusing doing this method will always work so how we split current is as follows we've got R1 R2 I want you to write down those resistors as a ratio R1 R2 then what I want you to do is I want you to write down the ratio of resistance so R1 is 5 ohms R2 is 10 ohms I want you to simplify that ratio so 5 goes into itself once 5 goes into 10 twice 5 to 10 is the same as 1 to 2 divide both sides of the ratio by five this what we've just written down this is the ra the ratio of resistance now what did we just learn about resistance and current they do opposite things so the smaller the resistance the bigger the current so what I want you to do and you will always do this when you are splitting currents is you take the ratio of resistances and you flip it so 1: 2 you must write 2: 1 that is what I now call the ratio of current if that's confusing why we do it just keep reminding yourself of the relationship small resistor R1 is small so 1 is smaller than two big current two is bigger than one okay so just flip the ratio so you write the ratio of resistances 5 to 10 simplifi it and flip it now what we're going to do is something that we did in grade n mass and grade 8 Mass where we split something into a ratio so you may have learned splitting into a ratio um differently in different ways but what you do is you add the parts of the ratio together so 2 + 1 is 3 2 + 1 is 3 and what we now do is we say okay if I want to work out the current going through R1 so I'm going to write that at the bottom here current in R1 what I do is I take the part of the ratio that corresponds to R1 so you follow R1 all the way down to the bottom it's two so you go two over three why over three because the total parts of the ratio is three so 2 corresponds to R1 and we're looking for the current in R1 2 over 3 because the total Parts is three times by the total current which is 6 amp I gave it to you over there so basically what I'm saying is the 1 ohm the sorry R1 the 5 Ohm resistor R1 gets 2/3 of the total current and 2/3 of the total current is 4 amp okay we can do the same thing but for the current through R2 so what you do is so that was current through R1 should actually use a different color here so let's use current through R1 is yellow okay current through R1 is yellow you go with you follow R1 all the way to the bottom to so current through R1 is 2 over 3 it's always over the total Parts times the total current so you always times the total current let's do it for R2 let's see if it makes sense so we take R2 remember R2 will get the rest of the current you follow it all the way down to the bottom it's 1 so we go 1 over 3 * the total current * 6 and that get you 2 Amp 1/ 3 * 6 so this is 2 over 3 * 6 this is 1 over 3 * 6 so in both cases you multiply by total current in both cases you're dividing by the total parts of the ratio for R1 you use two for R2 you use 1 and it makes sense think about it carefully so the total current is 6 amp R1 gets 4 amp R2 gets 2 Amp and we did say that the small smaller resistor will get the bigger currents the bigger resistor gets the smaller currents we also said R1 is half the size of R2 five is half the size of 10 and because R1 is half the size in resistance it gets double the current 4 amp is double 2 Amp I really really hope that that makes sense um I do suggest that you practice this I have more videos on this check out the links in the description box below but this is a summary of what we've basically learned today for series circuits versus parallel circuits and I hope that this has been helpful in the summary of Electro electricity for grade 10 please check out the links in the description box below I have past paper videos that you can go through um remember watch the video try the question unpause the video watch my explanation watch how we Mark the questions because that's how you're going to get top marks in the exam remember to subscribe for more videos like this I do physics chry and math and I'll see you in another video very soon bye everybody