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B1 Intermedio Inglés 14:48 Educational

The Big Misconception About Electricity

Veritasium · 27,133,374 vistas · Añadido hace 3 semanas

Estadísticas de aprendizaje

B1

Nivel MCER

5/10

Dificultad

Subtítulos (374 segmentos)

00:00

This video was sponsored by Caséta by Lutron.

00:03

Imagine you have a giant circuit

00:06

consisting of a battery, a switch, a light bulb,

00:09

and two wires which are each 300,000 kilometers long.

00:13

That is the distance light travels in one second.

00:16

So, they would reach out half way to the moon

00:19

and then come back to be connected to the light bulb,

00:22

which is one meter away.

00:24

Now, the question is,

00:25

after I close this switch,

00:27

how long would it take for the bulb to light up.

00:30

Is it half a second,

00:31

one second,

00:32

two seconds,

00:34

1/c seconds,

00:35

or none of the above.

00:37

You have to make some simplifying assumptions

00:39

about this circuit,

00:40

like the wires have to have no resistance,

00:42

otherwise this wouldn't work

00:43

and the light bulb has to turn on immediately

00:46

when current passes through it.

00:48

But I want you to commit to an answer

00:50

and put it down in the comments

00:52

so you can't say,

00:53

oh yeah I knew that was the answer,

00:55

when I tell you the answer later on.

00:59

This question actually relates to how electrical energy

01:02

get from a power plant to your home.

01:05

Unlike a battery,

01:07

the electricity in the grid

01:08

comes in the form of alternating current, or AC,

01:11

which means electrons in the power lines

01:13

are just wiggling back and forth.

01:15

They never actually go anywhere.

01:18

So, if the charges don't come from the power plant

01:21

to your home,

01:22

how does the electrical energy actually reach you?

01:27

When I used to teach this subject,

01:29

I would say that power lines

01:30

are like this flexible plastic tubing

01:33

and the electrons inside are like this chain.

01:36

So, what a power station does,

01:38

is it pushes and pulls the electrons back and forth

01:42

60 times a second.

01:44

Now, at your house,

01:45

you can plug in a device, like a toaster,

01:48

which essentially means

01:49

allowing the electrons to run through it.

01:52

So when the power station pushes and pulls the electrons,

01:55

well, they encounter resistance in the toaster element,

01:59

and they dissipate their energy as heat,

02:03

and so you can toast your bread.

02:05

Now, this is a great story,

02:06

I think it's easy to visualize,

02:07

and I think my students understood it.

02:09

The only problem is, it's wrong.

02:13

For one thing,

02:14

there is no continuous conducting wire

02:16

that runs all the way from a power station to your house.

02:20

No, there are physical gaps,

02:22

there are breaks in the line,

02:24

like in transformers

02:25

where one coil of wire is wrapped on one side,

02:28

a different coil of wire is wrapped on the other side.

02:30

So, electrons cannot possibly flow

02:32

from one the other.

02:34

Plus, if it's the electrons

02:36

that are carrying the energy

02:38

from the power station to your device,

02:41

then when those same electrons

02:42

flow back to the power station,

02:44

why are they not also carrying energy

02:47

back from your house to the power station?

02:50

If the flow of current is two ways,

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