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Circuits in Series and Parallel association

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Subido el 7 de noviembre de 2013 por Samuel E.

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An introduction to series and parallel circuits. From the distance learning course by Derek Owens

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Our next topic is series and parallel circuits, and before we get into the actual circuits and the concepts of series and parallel, we need to say a little bit about schematic diagrams. 00:00:00
Everything that electricians do is represented, or everything that they use is represented with a little symbol, and I've been drawing pictures of a simple circuit made of a battery and a light bulb, and I'll show you how we would represent this circuit schematically. 00:00:12
So let's draw the light bulb and some wires. 00:00:30
Okay, an electrician, if you were making an electrical diagram, 00:00:39
he would not draw a picture like the one I just drew. 00:00:42
There are three things in this picture. 00:00:47
There's the battery, the voltage source, there's the wires, and there's the bulb. 00:00:48
And he would draw the picture like this. 00:00:52
That little set of lines represents the battery. 00:00:55
And the wires would always be drawn with straight lines at right angles. 00:01:00
and the bulb would be drawn like this that little that little loop inside the bulb represents the 00:01:03
filament and then the wire coming down to the other side would look like that and for each 00:01:10
thing like a bulb for example you see that symbol and a battery for example you see that symbol 00:01:17
each thing that you can put in a circuit and there are lots of things besides batteries and 00:01:23
balls but each thing has its own symbol and you also might have a switch in here let me um put a 00:01:26
little gap in the wire and put in a switch something like that that might 00:01:32
correspond to a little switch here in the wire you could have a little device 00:01:40
here with a little switch that you could flip back and forth to allow the current 00:01:44
to flow or not but again you wouldn't draw an actual picture of the switch you 00:01:54
would draw this symbol which represents any switch now another thing that you 00:01:57
commonly see is not just a light bulb in a circuit, but 00:02:02
you see a resistor, which is represented by this zigzag 00:02:05
line. 00:02:10
So this circuit has a voltage source, V, and a resistor, R. 00:02:10
And the resistor could be anything. 00:02:14
It could be a toaster. 00:02:15
It could even be an electric motor. 00:02:16
It could be something that has electrical resistance. 00:02:17
It could be a heater, or it could just be a resistor, an 00:02:20
actual little device that is simply there to limit the 00:02:23
current flow. 00:02:26
It's actually pretty common to have a bulb and a resistor in combination. 00:02:28
So we might have a bulb here and a resistor there. 00:02:33
And the resistor keeps too much current from flowing through the bulb so that it doesn't burn out. 00:02:37
But again, the point here is that we have all these little symbols for the things in the circuits. 00:02:42
And the diagrams are done at right angles like this to keep them neat because they can get large and complicated. 00:02:46
Here's a picture of a circuit diagram for a solar panel regulator. 00:02:51
And there are lots of pictures like this that you can find on the web, on the internet. 00:02:56
If you want to build something, you can see diagrams of how to do it. 00:03:01
And they can get a lot more complicated than this. 00:03:05
And in a more advanced physics or electrical engineering class, you would become very familiar with diagrams like this. 00:03:09
Schematic diagrams. 00:03:15
Now let's talk about series and parallel. 00:03:17
Fundamentally, there are two ways in which resistors can be connected, or anything. 00:03:20
I'm going to be drawing these diagrams with resistors, 00:03:24
but you could be connecting resistors, light bulbs, toasters, anything. 00:03:27
And there's two ways that they can be connected to a battery 00:03:30
or some other voltage source. 00:03:32
They could be connected in series, which would look like this. 00:03:34
Here's the battery, and I'll draw a wire coming out here. 00:03:41
And then here's one resistor, and here's another, and here's another. 00:03:45
And the point here is that they're connected all three in a row. 00:03:52
So if you imagine the current flow, the charge comes out of the battery, flows around the circuit, 00:03:55
it goes through one resistor, then through the next one, and then through the third one. 00:04:01
And there's only one path. 00:04:05
It's like a one-lane road, or a one-lane loop road. 00:04:07
There's one way to go. 00:04:12
Every electron that comes out of the battery goes around and follows that wire, 00:04:13
goes through resistor A, and then resistor B, and then resistor C, and then back to the battery. 00:04:16
Now a parallel circuit is different. 00:04:22
In a parallel circuit, the current divides, so I'm going to orient this one a little bit differently, but here's a battery, and then imagine you have a wire coming out here, and then the wire comes over to this point and splits into three paths, so electrons coming out of the wire, they travel around the circuit this way, and then they divide. 00:04:25
Some of them go down this branch, some down that branch, and some down the third branch. 00:04:44
And you could have, on each branch, a resistor. 00:04:49
And then the electrons flow through those resistors, and then they all join back up. 00:04:57
And then the current flows back to the battery. 00:05:04
So the electrons all end up coming back and rejoining at this point, and then flowing back to the battery. 00:05:07
and the essential aspect of a parallel circuit is that the current divides and flows through multiple paths. 00:05:16
It doesn't have to be three, it could be two paths or four or a hundred. 00:05:24
The point is in a series circuit the current goes through one and then the other, all of them in a row 00:05:27
and in a parallel circuit the current divides. 00:05:33
Now one thing to note is that the actual geometrical layout of the resistors in your little circuit project 00:05:36
isn't the determining factor in whether or not the resistors are in series or parallel. 00:05:42
The determining factor is whether the current divides or not. 00:05:46
So in this case, for example, I have a resistor here. 00:05:49
And imagine the electrons flowing through it. 00:05:53
And then they come down and flow through this resistor. 00:05:56
And then they flow through this one. 00:05:59
And then they flow back to the battery. 00:06:03
Look at the actual physical layout on the screen here. 00:06:05
These three resistors are literally parallel to each other. 00:06:08
Those wires are parallel. 00:06:12
They form parallel lines. 00:06:13
but this is not a parallel circuit this is a series circuit and the reason is because the 00:06:14
electrons come out of the battery they flow through one resistor and then the next one 00:06:22
and then the next one all three in a row electrically this is no different from the 00:06:26
one we drew earlier like this the electrons flow through one resistor then another and then another 00:06:33
the electrons don't really know or care how the wires bend or how the circuit is shaped 00:06:39
What does matter is whether the current divides or not. 00:06:44
And if it divides into multiple paths, then it's a parallel circuit. 00:06:47
If the electrons go through one and then another and then another, then it's a series circuit. 00:06:51
Okay, a couple more comments about series and parallel circuits. 00:06:58
I've drawn two pictures here of light bulbs connected to a battery, 00:07:01
one in which they're connected in series and one in which they're connected in parallel. 00:07:06
And you can see in the series circuit, electric current flows through all three bulbs in a row. 00:07:11
And in the parallel circuit, it has to divide and goes through three different branches. 00:07:16
And that's the fundamental difference in the series and parallel circuits. 00:07:22
In the series circuit, current could be flowing through all of these bulbs, so they could all be sitting here shining. 00:07:25
But if one bulb burns out, that essentially breaks the circuit. 00:07:35
And it doesn't matter which bulb. 00:07:39
Suppose this bulb in the middle right here burned out. 00:07:40
So I'm going to scratch out the filament like the filament just burned out in that case the bulb will go out and 00:07:43
So will the other two because if this filament is dead if this filament in the middle bulb is 00:07:48
Broken then that's that's part of the path through which the electricity flows 00:07:54
And if you break that path then none of the electricity flows and when the when the current stops flowing the bulbs don't light in 00:07:59
The parallel circuit these three bulbs could be sitting here glowing all three of them are lit 00:08:06
and if one of them burns out suppose the one in the middle here burns out so I'll 00:08:14
I'll just scratch out the filament and it could break or crack the filament is 00:08:20
no longer conducting electricity that means electrons no longer flow down that 00:08:24
middle branch and so that bulb goes out but the other two bulbs remain lit you 00:08:29
can see that electrons can still form a complete circuit right there and they 00:08:35
can still travel through the third bulb like that right there it's only that 00:08:40
that one branch that's compromised by the breaking of that bulb, the other two will 00:08:46
continue to light. 00:08:50
And there's another effect that you should understand with series and parallel circuits, 00:08:52
and that's the effect of adding more bulbs. 00:08:56
If I start adding more bulbs in the series circuit here, remember that each bulb has 00:08:58
resistance, so adding more bulbs causes a greater total resistance, and that's going 00:09:04
to cause less current flow, and each bulb will burn less brightly. But because there's 00:09:10
less current flow, adding more bulbs causes less current to come out of the battery, and 00:09:16
the battery would end up lasting a little bit longer. And that should make sense too. 00:09:21
If the bulbs burn less brightly, the battery will last a little bit longer. So if they're 00:09:24
in series, adding more bulbs in series increases the resistance and decreases the current. 00:09:29
In parallel, the opposite thing is the case. If you add more bulbs in parallel, suppose 00:09:36
I come over here and add another light bulb over here I've added an additional 00:09:40
path through which current can flow and this is like adding more lanes on the 00:09:47
highway there's now an additional path that the electrons can take and the 00:09:51
result is more traffic you add more lanes in the road you get more traffic 00:09:58
there so adding an additional light bulb in parallel or more light bulbs in 00:10:02
parallel will decrease the overall resistance because you're adding more 00:10:07
paths for current to flow. All the light bulbs will continue to burn just as 00:10:11
brightly. What happens is the decrease in overall resistance results in an 00:10:15
increase in current flow. So you can take a little battery, a little flashlight 00:10:20
battery, and you can hook up 10 or 20 bulbs to it in parallel and they'll all 00:10:24
glow very brightly, but what happens is your battery will drain more quickly 00:10:28
because you're literally drawing more current out of the battery. If you hook 00:10:32
up 10 or 20 little flashlight light bulbs to a 00:10:36
a battery in series it's there's going to be too much resistance you won't see any glow at all 00:10:40
but if you come hook them up in parallel they'll all glow just as bright as normal 00:10:44
but you'll have decreased resistance and increased current flow 00:10:48
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Idioma/s:
en
Autor/es:
Derek Owens
Subido por:
Samuel E.
Licencia:
Reconocimiento - No comercial - Compartir igual
Visualizaciones:
15
Fecha:
7 de noviembre de 2013 - 15:00
Visibilidad:
Público
Centro:
IES JOAQUIN ARAUJO
Duración:
10′ 54″
Relación de aspecto:
1.76:1
Resolución:
480x272 píxeles
Tamaño:
10.56 MBytes

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