字幕表 動画を再生する 英語字幕をプリント Hi. It's Mr. Andersen and today I'm going to be talking about series and parallel circuits. These are a couple of different circuit diagrams. Remember this stands for a battery and each of those stand for a resistor. And so this would be a series circuit. Remember it's a closed circuit, so there's a loop where electricity can flow the whole way around. And then we have three resistors. And so the electricity that goes through this has to go through these as well. If we look at this one, this is one battery connected to three resistors as well, but they're parallel to one another. In other words there's three loops that that electricity can take and so we call that a parallel circuit. Now the first time you look at a series and a parallel circuit when it's actually connected, there's some stuff that's not super intuitive. In other words there's some weird stuff that takes place. But once you really understand what's going on in both a series and a parallel circuit, you'll do much better. And so today I want to show you basically a parallel and a series circuit, a few demonstrations. And I'm going to be using the Circuit Construction Kit. This is at phet.colorado.edu and I would encourage you to go there and play around with it. It's the best way to learn about electricity is to actually play around with it. Okay. So right here we've got two different loops. This one, this would be a battery right here. It's a 9-volt battery. This is an ammeter which is going to measure the amps. We've then got wires connected to a light bulb back to a switch and then back to the battery again. And so this would be a series circuit because electricity is going to flow is this direction through the battery and then back, through the bulb and then back again. And so what I turn it on we can see that electrons are flowing. We've got 0.90 Amps and then it's running through a light bulb. And so these rays around the outside of the light bulb show you how much light is being given off from that. And so the first thing I'd like to do, let me turn that off for just a second. So let me open that circuit for a second, is kind of get a sense for how much electricity is coming out or how much current is flowing through there and how much light are we getting off of that. And now I'm going to add another light bulb and I'm going to put it in series. So let me add another light bulb here, and I have to break this with a junction and let me connect to both sides of that. And let me move it down so it looks a little better. Okay. So now we've got two light bulbs, we've got the same battery, you kind of remember how much light we were getting out of it before and you remember the speed. And so let's turn this one on now. Okay, so in a series circuit what we have now is those two bulbs are not as bright and the reason why, if you remember how much speed we were getting, how much current we were getting, remember it was 0.90 amps. And so in a series circuit, if we add more resistance we're going to decrease the amount of current. And as a result we are going to have dimmer light bulbs. And so the current is going to be the same through every component in a series circuit. And so the other thing about a series circuit is let me try, let me remove this. So let me split the junction. Okay. So when I split the junction there I cut that wire and so it wasn't connected anymore and so both bulbs went out. And so the two things you should learn number 1 is that in a series circuit all of them have to be working for a current to flow and the second thing is that they all have the same amount of current. Volts is another thing. And so let's add a volt meter as well. So if we add a voltmeter, this is a 9-volt battery, if I look on either side of the light bulbs we'll find that the volts are 9.00 volts. If I move this lead over here, this electrode over here, we find that it's 4.50 volts. And then if I shift both of them to this side of that light bulb is 4.5 as well. And so the sum of the volt or the voltage drop between the two components in that are going to equal the volts that we have for the whole thing. And so it's 9 volts, but then each of those bulbs is going to be a drop of 4.5 volts. So we have 9 volts and then we have 0 volts when we get to the other side. So let's get rid of that volt meter and let me turn this one off. And so let's return that for a second. Get a sense of how much light we are getting from these two light bulbs, and we have 0.45 Amps. And now we're going to look down here at a parallel circuit. And so a parallel circuit there are two parallel pathways. In other words there's a wire that goes through this bulb and a wire that goes through this bulb. And so when I turn this on there's a clear difference between the two. And the first time I saw this it was totally confusing to me. In other words these two light bulbs are as bright as that one light bulb was before, when it wasn't in series. And so the first thing that should stand out to you is that these two bulbs are as bright as that one bulb before it was hooked up in series. And so another thing that's happening is that we actually have way more amps moving through this. And so you can see that the electrons are moving more quickly. And so the difference between a series circuit and a parallel circuit is that the current is actually increased. Remember when we had, let's go back and remove this and just connect it together, so remember here we had 0.90 amps for one light bulb, but here we now have 1.8 amps. In other words the electricity is actually flowing faster. Why is that? Well here there is the current of this thread and there's the current of this branch and the two currents together are going to sum up to this current. And so before when we were saying the voltage dropped in each of those sums up to the voltage of the battery, well in a parallel circuit those two pathways, in other words those two currents are going to sum up to the current of that, the whole branch. Another thing that happens in a parallel circuit, let's kind of remove this light bulb, and so remember when I removed a series light bulb the whole thing went out, but in a parallel circuit when I remove one of those light bulbs, the other one keeps moving. Now you should've seen that when I removed that light bulb the Amps dropped down to 0.90 and electricity isn't flowing through this side. But by hooking it up this way we've now got electricity or a path for electricity to go. When I was a kid I remember we had a string of light bulbs that were hooked up in series and it was the most annoying light bulb strand that you could have for Christmas lights because if you ever had one bulb go out, on a series circuit, then the whole thing was broken all the way down. So you had to search through that string of lights until you found the one that was burnt out. Now they use parallel circuits and the reason they do that is you don't get that drop in current with each bulb. And the other thing is that you can have a break in one of the bulbs and the other ones are all going to work. And so that's kind of an introduction to series and parallel circuits. Remember in a series circuit the current is going to be the same through every part of that loop. But in a parallel circuit it's going to be the sum of the two will be the sum of the current through the whole circuit. And the voltage drop if we add our voltmeter, in a parallel circuit it's going to be the same along each thread. So remember this would be a 9.00 volt on this pathway, but it's also going to be a 9.00 volt on this pathway. And so you're not getting anything for free with a parallel circuit, you're actually going to go through more energy using this set up then you would over here because you're gathering more amps. So that's parallel and series circuit and I hope that's helpful.