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Hi. It's Mr. Andersen and today I'm going to be talking about series and parallel circuits.

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These are a couple of different circuit diagrams. Remember this stands for a battery and each

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of those stand for a resistor. And so this would be a series circuit. Remember it's a

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closed circuit. So there's a loop where electricity can flow the whole way around. And then we

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have three resistors. And so the electricity that goes through this has to go through these

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as well. If we look at this one, this is one battery connected to three resistors as well.

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But they're parallel to one another. In other words there's three loops that that electricity

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can take. And so we call that a parallel circuit. Now the first time you look at a series in

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a parallel circuit when it's actually connected there's some stuff that's not super intuitive.

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In other words there's some weird stuff that takes place. But once you really understand

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what's going on in both a series and a parallel circuit you'll do much better. And so today

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I want to show you basically a parallel and a series circuit. A few demonstrations. And

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I'm going to be using the circuit construction kit. This is at phet.colorado.edu. And I

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would encourage you to go there and play around with it. It's the best way to learn about

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electricity is to actually play around with it. Okay. So right here we've got two different

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loops. This one is a, so this would be a battery right here. It's a 9 volt battery. This is

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an ammeter which is going to measure the amps. We've then got wires connected to a light

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bulb, back to a switch and then back to the battery again. And so this would be a series

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circuit because electricity is going to flow in this direction through the battery and

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then back, through the bulb and then back again. And so when I turn it on we can see

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that electrons are flowing. We've got 0.9 amps and then it's running through a light

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bulb. And so these rays around the outside of the light bulb show you how much light

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is being given off from that. And so the first thing I'd like to do, let me turn that off

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for just a second. So let me open that circuit for a second. Is kind of get a sense for how

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much electricity is coming out or how much current is flowing through there and how much

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light are we getting off of that. And now I'm going to add another light bulb. And I'm

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going to put it in series. So let me add another light bulb here. And I have to break this,

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split the junction. Connect to both sides of that. And let me move it down so it looks

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a little better. Okay. So now we've got two light bulbs. We've got the same battery. You

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kind of remember how much light we were getting at it before. And you remember the speed.

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And so let's turn this one on now. Okay. So in a series circuit what we have now is those

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two bulbs are not as bright. And the reason why, and if you remember how much speed we

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were getting, how much current we were getting, remember it was 0.9 amps. And so in a series

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circuit if we add more resistance we're going to decrease the amount of current. And as

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a result we're going to have dimmer light bulbs. And so the current is going to be the

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same through every component in a series circuit. And so the other thing about a series circuit

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is let me try, let me remove this. So let me split the junction. Okay. So when I split

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So when I split the junction there, I cut that wire and so it wasn't connected anymore.

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And so both bulbs went out. And so the two things that you should learn, number one is

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that in a series circuit all of them have to be working for current to flow. And the

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second thing is that they all have the same amount of current. Volts is another thing.

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And so let's add a voltmeter as well. So if we add a voltmeter, this is a 9 volt battery.

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If I look on either side of the light bulb we'll find that the volts are 9 volts. If

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I move this lead over here, this electrode over here, we find that it's 4.5 volts. And

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then if I shift both of them to this side of that light bulb it's 4.5 as well. And so

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the sum of the volt or the voltage drop between the two components in that are going to equal

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the volts that we have for the whole thing. So it's 9 volts. But then each of those bulbs

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is going to be a drop of 4.5 volts. So we have 9 volts and then we have 0 volts when

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we get to the other side. So let's get rid of that volt meter. And let me turn this one

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off. And so let's return that for a second. So get a sense of how much light we're getting

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from these two light bulbs. And we have 0.45 amps. And now we're going to look down here

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at a parallel circuit. And so a parallel circuit there are two parallel pathways. In other

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words there's a wire that goes through this bulb and a wire that goes through this bulb.

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And so when I turn this on there's a clear difference between the two. And the first

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time I saw this it was totally confusing to me. In other words these two light bulbs are

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as bright as that one light bulb was before when it wasn't in series. And so the first

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thing that should stand out to you is that these two bulbs are as bright as that one

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bulb when it was, before it was hooked up in series. And so another thing that's happening

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is that we actually have way more amps moving through this. And so you can see that the

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electrons are moving more quickly. And so the difference between a series circuit and

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a parallel circuit is that the current is actually increased. Remember when we had,

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go back and remove this and just connect it together. So remember here we had 0.9 amps

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for one light bulb. But here we now have 1.8 amps. In other words the electricity is actually

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flowing faster. Why is that? Well here there is the current of this thread. And there's

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the current of this branch. And the two currents together are going to sum up to this current.

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And so before when we were saying the voltage drop in each of those sums up to the voltage

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of the battery, well in a parallel circuit those two pathways, in other words those two

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currents are going to sum up to the current of the whole branch. Another thing that happens

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in a parallel circuit, let's kind of remove this light bulb. And so remember when I removed

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a series light bulb the whole thing went out. But in a parallel circuit when I remove one

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of those light bulbs. The other one keeps moving. Now you should have seen that when

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I removed that light bulb the amps dropped down to 0.9. And electricity isn't flowing

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through this side. But by hooking it up this way we've now got electricity or a path for

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electricity to go. When I was a kid I remember we had a string of light bulbs that were hooked

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up in series. And it was the most annoying light bulb strand that you could have for

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Christmas lights. Because if you ever had one bulb go out on a series circuit then the

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whole thing was broken all the way down. So you had to search through that string of lights

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until you found the one that was burned out. Now they use parallel circuits. And the reason

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they do that is you don't get that drop in current with each bulb. And the other thing

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is that you can have a break in one of the bulbs and the other ones are all going to

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work. And so that's kind of an introduction to series and parallel circuits. Remember

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in a series circuit the current is going to be the same through every part of that loop.

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But in a parallel circuit it's going to be the sum of the two will be the sum of the

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current through the whole of the circuit. And the voltage drop, if we add our voltmeter

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in a parallel circuit, it's going to be the same along each thread. So remember this would

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be a 9 volt on this pathway. But it's also going to be a 9 volt on this pathway. And

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so you're not getting anything for free with a parallel circuit. You're actually going

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to go through more energy using this setup than you would over here because you're actually

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gathering more amps. So that's parallel and that's series circuit. And I hope that's helpful.