Beginner Electronics

Beginner Electronics – 17 – Series and Parallel

what is going on everyone my name is Gautam or and welcome back to electronics episode 17 in this episode we are going to talk about series and

parallel circuits which are extremely important to understand because whenever you're doing electronics work you're going to be using either one or the other or even both at the same time and

I'm going to try and explain them as best as I possibly can so I have two circuits up here now I have just some random resistors in these circuits but of course these don't have to be

resistors these can be LEDs or any other electronics component because any electronics component for the most part has resistance so even an LED has some internal resistance but anyways I'll

just use resistors for these examples on the left here we have something similar to what we built back in episode number 8 or something like that where essentially we had a battery right here

and then we had a resistor then we had an LED and then that just went right back to the battery after that means the electricity could just travel in one big loop just like this right here

electricity is just going to travel in one direction in one gigantic loop something like this is called a series circuit and that's the only type of circuit that we've worked with this far

but let's take a look at the circuit over here on the right this is a bit different we still have three resistors all the same resistors and we still only have

one battery except electricity doesn't have one path it can travel through it can travel through this resistor right here it can travel around to the second resistor back to the battery and it can

even travel all the way through to the third resistor and back to the battery there's multiple paths for the electricity to travel through now we've never worked on something like this but

something that has multiple paths for the electricity to travel through is called a parallel circuit and we will be working with parallel circuits very shortly but let's get the main

differences about these two circuits because we have to understand when and why we use which type of circuit so I'll begin with a simple example in your house you have most likely quite a few

kitchen appliances so you have maybe a refrigerator a microwave and we'll say a coffee maker and all three of them are just plugged into an outlet in your house so we can say that in this series

circuit r1 is maybe your refrigerator maybe artoo is your coffee maker and r3 is your microwave and they're all getting power and they're all running just fine

but then all of a sudden you decide to unplug your coffeemaker so you essentially just remove this resistor you remove the coffeemaker from the circuit and now electricity has no path

to travel through electricity will try to travel by opes you unplug the thing and now it can't travel through it to get to the other appliances that means your refrigerator in your microwave both

stopped working just because you unplugged the coffeemaker as another example let's say you have a string of Christmas lights so you can just picture that each

resistor here is just another light in that string of Christmas lights they all work perfectly except when one of the lights burns out if say this middle light right here burnt out then all of

the other lights are gonna stop working because you create an open circuit now there's no pathway for the electricity to travel through so serious circuits are actually a really bad design for

many things like the wiring in your house that you plug appliances into and Christmas lights of course because in a giant string of Christmas lights there's bound to be at least one light that goes

out once in a while so we fix that by using parallel circuitry if we have the same setup of Christmas lights in a parallel circuit so picture each resistor here being a separate Christmas

light in that Christmas light strand then they're all going to work perfectly and if the second or the middle Christmas light goes out then this pathway is broken however the other two

lights are still going to work because electricity still has a path through the first light and it can still have a path through the third light here that means the only light that goes out and the

Christmas lights are just going to be the middle one because it burned out and now there's no path of electricity through the middle one and if we bring this back to your house let's say and

each resistor was a different appliance if you unplug one of the appliances then the other appliances will still have a path for electricity to travel through so that's a big advantage to parallel

circuits now we have these two different types of circuits except there's some pretty big differences between them in a series circuit current which remember is I is the same at all points in the

circuit where voltage can differ at different points in the circuit like we've seen before let me rewrite that that looks very bad differ so if we took a multimeter and we measured current at

any point in this series circuit absolutely any point and we did it properly then we would get this same exact reading in a series circuit current stays the same but voltage will

differ so if we measure the voltage across this r1 right here we might get a different voltage from the voltage across our three down here so voltage can differ but current stays the same

now if we take a look at a parallel circuit however it's the opposite current can differ at different points within the circuit but voltage stays the same in a parallel circuit so if we

measured the voltage across R one right here and we measured the voltage across R three right here and we measured the voltage across r2 we should get the same exact voltage reading however the

current off of these multiple branches might differ or one might have a higher current than r3 does so those are some pretty big differences that we're going to have to take into account in the

future mome we're working with this now let's talk about adding resistors what is the total resistance in a series circuit well it's just going to be our total I'll just do our tought so the

total of resistance in a series circuit is going to equal to all of the resistances added up so in our case it would be r1 plus r2 plus r3 if you had more resistors so that's the total

resistance in a series circuit what about a parallel circuit though parallel circuits are actually quite different in a parallel circuit one over the total resistance in a parallel circuit is

equal to one over all of your resistance values added so one over r1 plus one over r2 two plus one over r3 if you had more resistors and we'll do some examples with this that way we can

understand the math maybe a bit better but for right now that is the difference in the total resistance and it's quite drastic what this means is that if you add a

resistor so if we add a resistor into a series circuit our total the total resistance in that circuit is going to increase it's going to go up that's pretty obvious because we're just adding

another resistor onto this total value however in a parallel circuit if we add a resistor so we just add another resistor in another branch or whatever then our total resistance R T ot is

actually going to decrease the total resistance in the circuit is going to decrease and we're going to see this when I do an example in just a second now when you add a resistor in a series

circuit not only does your total resistance go up like it should but your current actually decreases because you're adding more resistance and by Ohm's law V equals I R if we're adding

more resistance than current must decrease but if we look at parallel you might have guessed it if we add resistance resistance total will decrease therefore your current

throughout the entire circuit is going to increase and remember current in a parallel circuit can be different at different points all right so we know the main differences between a series

and a parallel circuit we've made a series circuit before but we haven't made a parallel circuit yet now let's get to some examples so we can actually understand how to calculate all this

properly and trust me it's very important we have a 9-volt battery and we have some resistors in parallel so let's find the total resistance of the circuit now remember 1 over the total

resistance is going to be equal 1 over all of our resistance values added up so in our case we're going to have 1 over 8 plus 1 over 4 plus 1 over 2 and that is the same thing as I believe it should be

7/8 now this means that our total is just going to be equal to the reciprocal of our result or 8 over seven ohms as our total resistance in the circuit now if

you're on a calculator and you want to do this then you can simply do all of this work right here 1 over 8 plus 1 over 4 plus 1 over 2 and just raise that to the power of negative

one and that will get you the correct result if you're on a calculator anyways we now know the total resistance of the parallel circuit now let's go ahead and find the total current within our

parallel circuit now if we were in a series circuit we know that current stays the same at all points except we are instead in a parallel circuit so we can actually calculate current at

different points first of all though I jumped ahead of myself let's find the current or the total current of the circuit total current by Ohm's law V equals IR is going to equal V over our

voltage over resistance we know the total voltage in our circuit is just nine volts like I put it so nine over our 8/7 which is our total resistance and that if we do that out on the

calculator that is about seven point eight seven five amps so that is the total current that is traveling through the circuit right here that's quite a bit of current seven point eight amps

but anyways let's figure out how we get to this total current in other words let's measure how much current that each component each resistor is getting so we'll calculate it first for the eight

ohm resistor and we can just use Ohm's law once again so we know that voltage stays the same so I is going to equal V over R as always so I is going to equal nine volts over and since we're

calculating the current from just this one component we're going to use the normal resistance value so nine over 8 ohms is what that would be and that's the current for resistor one will

calculate the current for resistor two and the current for resistor three go ahead and do that yourself right now all right I've made a huge mistake that is not ohms these are amps of course

we're not measuring resistance I is current so here are all the three correct currents that are passing through each resistor here and if we add them all up

we get seven point eight seven five amps which is the same thing as we calculated as the total current running through our circuit so that adds up that's proper that means we hopefully did everything

correct and just to prove that voltage in a parallel circuit stays the same throughout we should be use Ohm's law once again to go ahead and calculate that for each individual of

resistor so for instance the voltage going through the first resistor is just going to be equal to the current going through the first resistor which in this case is nine over eight amps so nine

over eight amps times the resistance value in this case it's eight like so and that equals out to nine volts and if we did that for the second and third resistors and any other resistor or

component that's in parallel we would get nine volts in this case because we have nine volts running through our circuit all right that's awesome we've learned two

different types of circuits and I'm sorry that this video is so long but I really have to push these two types of circuits because we will be working with them quite a bit now what happens if we

added a resistor right here in the middle of our wire here and we'll say that that resistor is I don't know a 4 ohm resistor all right what I have here is the exact same circuit that I just

drew just drawn a little bit differently that way you can clearly see that we have a parallel part of the circuit and if you thought of this parallel part of the circuit as just one little thing

then we can see the series part of the circuit runs from the battery through this first resistor into this block of mystery parallel illness and then comes right back on out just like a series

circuit having one path of electricity so these three resistors are all in parallel that should be hopefully clear to see and we have this one outside resistor that is in series instead now

in a series circuit our voltage doesn't stay the same that means we're going to have some voltage drop across this resistor so we're going to say that the voltage drop VD however to calculate the

voltage drop across this first resistor here we're going to need the current going through the series part of the circuit now in a series circuit current remains the same everywhere so to

calculate current we're going to need the total voltage which is nine volts and we're also going to need the total resistance so remember how I said earlier that we can just think of this

parallel part of the circuit as being just sort of its own electronics component in a way so think of this as just one gigantic resistor now if we're going to think of the

as one gigantic resistor we're going to need to figure out how much resistance it is and we already calculated that using one over the resistance total is equal to 1 over 8 plus 1 over 4 plus 1

over 2 and we got that the total resistance for the parallel part of the circuit is 8 over seven ohms so to find the total resistance in the series part of the circuit we just have to add 4

ohms to that 4 ohms Plus this giant component that we said which is really the parallel part of our circuit so plus 4 ohms and that will get us the total resistance in this series part of the

circuit and I'll just keep it simple for and 8/7 ohms now still before we can calculate this voltage drop of this resistor up here we're going to need to find the total current running through

the series part of the circuit this shouldn't be too bad because we already know Ohm's law will say I s so the current in this series part of the circuit or essentially throughout this

entire thing for the most part is just going to be equal to so is equals our voltage over our resistance we've used this many times before which is just going to be our 9 volt power supply

divided by the total resistance in the series part of the circuit which in our case is 4 and 8 7s ohms so divided by four and eight seven ohms and if we do the math correctly that should be 1.75

amps so the total current running through the circuit is 1.75 amps now that we have total resistance and total amperage which we found using the total resistance we should be able to find the

voltage drop across the 4 ohm resistor in series up here but the simple formula of V equals I R so current which we found is 1.75 amps multiplied by the resistance of the resistor we're finding

the voltage drop of which is 4 ohms multiplied before and that will equal 7 volts great so why did we find the voltage drop across this resistor well we found it because if the resistor is

taking up 7 volts from the battery and the voltage in the parallel part of the circuit must stay the same then what's the voltage in the parallel part of the circuit well since the

resistor takes up seven volts we're only going to have so many volts going into the parallel part and that should be easily found because we know we have our nine volt power supply minus the voltage

that this resistor up here is taking so minus seven volts that leaves us with two volts so two volts should be coming from this resistor over here and into the parallel part of the circuit

therefore we'd have to redo all the calculations that we did just minutes ago to find out the current in each one of these resistors but nonetheless we now know that the voltage through each

one should stay at a constant two volts instead of nine volts because we have this pesky resistor here so I challenge you guys to go ahead and do the same calculations that we did just minutes

ago to find the current through each one of the resistors make sure everything adds up properly the total current in the parallel part and if you can do that successfully then you know more about

series and parallel circuits than you probably think you do I'm really sorry for the long video guys but it was really important that we touched a lot upon this and a lot upon the math that

way we can do it fairly quickly when we get to more and more advanced circuits thank you guys so much for watching and I hope to see you guys in the next episode

We talk about two different types of circuits; series and parallel!

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