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• 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.

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

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# 直列回路と並列回路 (Series and Parallel Circuits)

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kiss08099 に公開 2021 年 01 月 14 日