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More On Circuits

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Why? Files segment exploring circuits in more depth.

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Now we've learned all about series and parallel circuits and we're ready to see how our houses are wired. 00:00:00
The model of a house right here. 00:00:05
How can we tell whether it's wired in series or in parallel? 00:00:07
Well, we know that when something is wired in parallel, 00:00:10
when one lamp burns out or is turned off, the rest of them stay on. 00:00:13
Not only that, but the lights that are still on don't change. 00:00:16
They don't get lighter and they don't get dimmer. 00:00:19
Let's try it. Let's turn one of these lamps off and see what happens. 00:00:22
They must be in parallel because in series, 00:00:26
all of the lights would have gone out when one was turned off. 00:00:28
Why is it important to have a house wired in parallel? 00:00:31
Well, it'd be really annoying if I was playing on the computer 00:00:34
and my dad turned a lamp off and the computer shut off. 00:00:37
Or if I was in my room and my light got dimmer 00:00:40
because someone else was turning lights on in the house. 00:00:42
As more and more devices are turned on in the house, 00:00:45
the number of charges flowing through the circuit increases. 00:00:48
Each device gets just the current that it needs, 00:00:51
but the current flowing in the supply wires must supply current to all the devices. 00:00:54
If too many devices are turned on, 00:00:58
the current in the supply wires is too great and the wires get hot. 00:01:00
This is called an overload. 00:01:03
The circuit breaker trips and turns the circuit off. 00:01:05
I guess the circuit breaker is in series with everything else. 00:01:07
When it is turned off, we have an open circuit. 00:01:10
Why would you want everything in the circuit to turn off? 00:01:13
Because if the wires in the walls get too warm, 00:01:15
then you'd have a fire on your hands. 00:01:17
That's right. 00:01:19
Now sometimes an appliance malfunctions and causes a short circuit. 00:01:20
It basically means the two incoming wires touch. 00:01:24
There's a huge current that runs through because it's bypassing the load. 00:01:27
Now when a short circuit occurs, what happens? 00:01:30
So the circuit breaker opens the circuit, so no harm is done. 00:01:33
That's right, just like this. 00:01:36
So when a circuit breaker is tripped, you have to first fix the problem 00:01:38
and turn the circuit breaker back on. 00:01:41
Just like several wall outlets in a house are connected together 00:01:43
and protected by a circuit breaker, 00:01:46
the houses in a neighborhood are also connected together in this parallel circuit 00:01:48
and protected by a big circuit breaker. 00:01:52
So how many houses are in a circuit? 00:01:54
Could be as many as four or five. 00:01:56
Does this mean if there's too much current going into a house in the circuit, 00:01:58
the circuit breaker opens the circuit? 00:02:01
That's right. When the circuit is open, all the houses go dark. 00:02:03
Wow, we may be onto something here. 00:02:06
But what could cause too much current to go to the houses? 00:02:08
I guess the circuit breaker isn't working. 00:02:11
No, I think it's more of a problem with the wires running to the houses. 00:02:13
Maybe there's a short circuit in the wires. 00:02:17
Good thinking. 00:02:19
Why didn't we think of this earlier? 00:02:20
Maybe because the electrical wires in our neighborhood are buried underground. 00:02:22
That way, the short circuit could be hidden from view. 00:02:25
This could be tough. 00:02:28
Hey, Dr. D., have you had any luck with your train? 00:02:30
Nope. I checked out the power unit on the workbench last night, 00:02:32
and it is indeed working. This is really getting puzzling. 00:02:37
Wait a minute. Talking about series and parallel circuits 00:02:40
reminds me of something else to check on the train. 00:02:44
What's that? 00:02:46
Well, the pieces of track form a series circuit. 00:02:47
If one of the links of track is not properly plugged in, 00:02:50
we have an open circuit. The train won't work. 00:02:53
I'll check on that later. 00:02:55
In the meantime, I think we should revise our hypothesis to 00:02:57
there is an open circuit somewhere between the power source 00:03:00
and the houses across the street. 00:03:03
Well, good luck on solving your mystery. 00:03:05
It sounds like you're getting close. 00:03:07
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Idioma/s:
en
Niveles educativos:
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Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
663
Fecha:
28 de mayo de 2007 - 15:34
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
03′ 09″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
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480x360 píxeles
Tamaño:
19.04 MBytes

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