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hi good morning to everyone here we are I'm going to explain the the end of the

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the unit okay and don't worry if you haven't understand everything till now

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because we are going to have a we are half we are going to have one or maybe

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one more than one online classes to explain all your questions okay so this

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last part will be explained in this video okay and I'm going to explain the

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things that I I think are more important in the unit of electricity okay so and

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before this okay you have calculated some values using the Ohm's law we're

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going to do more exercises but because I think you have some doubts about about

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it but just before we're going to conclude the unit explaining the types

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of circuits okay there are three these three circuits are the the types of

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circuits okay and how can we distinguish them and looking how the

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resistances are situated are connected in this industry and we have a serial

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circuit if the resistances are connected like this like this okay one and then

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another one and then another one okay a parallel circuit it's not this kind of

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connection parallel circuit is something like this we have resistances sorry

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because some some of you now doesn't know what is this this is a resistance

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this is another resistance this is another resistance this line this line

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this line are pieces of wire okay come on let's do some resistances I transform

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like this okay but you can see both of them okay and this is the wire okay we

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have this different connection between resistances and they don't look similar

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to this one the how can we distinguish it with a trick thinking about the

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intensity intensity is the is like the imagine a motorway motorway is the wire

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in electrical circuits in an electrical circuit and the intensity more or less

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it's not exact these are there is the the are the cars okay the cars on the

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motorway okay so if the intensity comes here the cars yeah all the cars are

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going to pass this resistance then all the cars are going to pass all this

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resistance and then all the cars are going to pass this resistance okay okay

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this is a little bit difficult but in this case all the intensity gets get

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this point okay this point and then the intensity must be divided in two ways

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one amount of intensity in this way and one amount this way okay so an example I

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told you about the cars and motorway this is a motorway and here you have a

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cross okay you have a you need to to choose which way way to Mahala on the

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way to Madrid okay so some cars are going to take this way and some cars

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going to take this way okay so if and then passing this resistance all the

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cars from Mahala on the and from Madrid both both get this point okay and then

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they go they go together from this point till the end of the wire okay I don't

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know if you are understanding me 100% okay but this more like more or less

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this okay we have if we don't have if we don't have a split of intensity like

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here if all the cars take the same way we have a serial circuit if we have a

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division of intensity we have a parallel circuit and what is a mixed circuit so

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maybe some of you already know that mix it and a circuit is a combination of

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both circuits okay something this is the simplest one

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we have another possibility that is as simple as this one okay so in this case

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this case all the cars all the cars pass pass by this resistance so this

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resistance is serially connected to this second part okay and how are these

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two resistances connected and both are parallel okay from here the cars must

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must divide the amount of cars I don't know if you understand me okay and we

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have all the intensity crossing passing by this resistance but from this point

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till this point we have a division of intensity some amount of intensity take

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this way and some some amount of intensity take this another way so we

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here we have part that is serial and this part is parallel so both together

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are a mixed circuit okay more or less I have explained I have explained

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everything here you have almost almost I have explained almost everything so what

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is missed till now this how to calculate the total resistance of a

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circuit this is the most important part and this sometimes is difficult it's

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hard for you to do this properly okay so let me do an example

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for instance we have this circuit two resistances connected okay not two, three

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and here these three resistances as the title of this part says are connected

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and serial in a serial way okay serial okay so the value of this resistance is

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two this is four this is five this is not okay this is wrong we need the units

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which unit which unit do we use to measure resistances this one ohms okay

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ohms ohms because of the Greek letter Omega this is Omega okay Omega everything

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let me do it again very fast one resistance second resistance and third

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resistance okay two ohms four ohms and five ohms okay so if the resistances are

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in this way they and they are serial circuit so we use this formula to know

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the total value of the resistance so how can we calculate the total value of the

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resistance of these three resistances connected just adding one by one two

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four and five eleven what 11 ohms that's all okay this could be an example okay

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this could be an exercise or an exercise calculate the total resistance of this

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circuit so serial circuit serial circuit so we do this okay if the

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circuit is parallel we we don't do this in fact this is wrong if in a in a

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parallel circuit so it's very important to think before if think before which

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circuit is in the exercise okay so and just to finish we're going to do an

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exercise with them with a parallel circuit okay

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parallel circuit here before yeah so we don't say yeah both are examples of

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serial circuits serial circuits okay here we have a battery have a switch

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lamp okay both I don't know if you see this both are the same same circuit this

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is this circuit is drawn with using symbols and this one with with pictures

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of the symbols okay this battery is this okay this is the battery and symbol this

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is a switch okay here the switch is open and this is both are lamps lamps

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okay okay so let's carry on to to to parallel circuit okay in a parallel

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circuit we have this difficult formula okay for I'm going to explain you to to

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help you with an easier form okay so we have this example I'm going to use the

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easiest one not this three resistances again okay so this resistance I don't

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now two ohms this one six ohms and this one 12 ohms okay R1 R2 R3 resistance one resistance

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two resistance three are connected this is a parallel circuit because the intensity

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comes here the cars go together to this point and then they divide in three parts okay so

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how can we calculate the total resistance here how can we calculate this is the hardest

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thing probably the hardest hardest thing of the whole year okay how to calculate this

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because of the this formula okay so calculate RT we're going to use this formula one over

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RT is one over R1 plus one over R2 plus blah blah blah so one over two one over six one

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over twelve okay are you following me let these values come from here okay six twelve

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okay let's let carry on okay so we need to remember how to do this we need to use we

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need only one number here below okay so which is the minimum common multiplier so a minimum is

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12 so 12 divided by 2 6 multiplied by 1 6 plus 12 divided by 6 2 here 12 divided by 12 1 so here

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we have 6 9 over 12 um is this the total resistance no no no no no no no this is the

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most common error most common error okay no RT okay it's not RT this because it's easy I think

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it's easy to see we are calculating 1 over RT 1 over RT so 9 over 12 is 1 over RT but I'm asking

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you to calculate RT no I'm not asking 1 over RT okay so what we we need to do to swap swap

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one over RT so RT over 1 RT is 12 over 9 ohms we can divide this 4 divided by 3 ohms and this

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is this is one point three three three three three three okay three I'm not going to use the

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symbol of periodic okay this is the value of the total resistance of this parallel circuit okay

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let me tell you something when we calculate a parallel circuit always the result must be less

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than the lowest value of the resistances here okay we have three resistance values 12 6 2 the result

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always has to give less than the lowest value of the resistances if it gives more than any of these

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the exercise is already wrong, okay, the cars come here, they are divided, okay, they are divided if they are

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divided, the parallel circuit is divided, if the cars are divided, the resistance, let's say the load

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of the entire circuit, let's say it is less, I don't know if you understand me, the cars come down a road

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here there is a division of roads where the cars can be divided the traffic is going to be reduced

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if the traffic is reduced the resistance of the road if you want to understand it is less the traffic

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will be less in its set of agreement you have to understand what I say if we only put a resistance

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in series because it is good it will give us something else different the trick I explain it in case the

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trick is worth for two resistors but it can be expanded for 3 and for 4 for the ones we want

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but we always have to do two in two we have for example this value of resistance 2 and 6

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for example 26 in parallel how to calculate total resistance if we wanted to do it by the

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formula that is up there we can do it but in the direct way we can put rt directly

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rt is equal to the product of these two

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2 times 6 and between the sum

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2 times 6 is 12

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and 2 plus 6 is 8 and this would be the value of the total resistance of this circuit but it is only

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valid for 2 if we want to do it for 3 we would have to do this parallel first what we are going to do

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is this just and the result to make the parallel again with this you understand what I say, that is,

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we have just calculated 2 and 6, it gives us 12 octaves that we can divide by 4, it gives us 3

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means, not 3 means, which is 1.5, because if now we do 1.5 ohms, the units are important,

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because now we do this again but with 1 and 5 1.5 and 12, that is, we multiply 12 by 1.5, we

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divide it by 12 plus 1.5, it gives us the same again, try to do it and you will see that it gives you the

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same value if it does not give us that or two things or you have done it wrong or you have understood it wrong ok

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and nothing else I leave you some exercise to do in relation to this ok I leave you all this

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week to do a hug and be careful there will be ok exercises of mixed circuits we are not going to

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do ok we are not going to have this course and with this it will be enough