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The Big Misconception About Electricity
Statistiques d apprentissage
Niveau CECRL
Difficulté
Sous-titres (374 segments)
This video was sponsored by Caséta by Lutron.
Imagine you have a giant circuit
consisting of a battery, a switch, a light bulb,
and two wires which are each 300,000 kilometers long.
That is the distance light travels in one second.
So, they would reach out half way to the moon
and then come back to be connected to the light bulb,
which is one meter away.
Now, the question is,
after I close this switch,
how long would it take for the bulb to light up.
Is it half a second,
one second,
two seconds,
1/c seconds,
or none of the above.
You have to make some simplifying assumptions
about this circuit,
like the wires have to have no resistance,
otherwise this wouldn't work
and the light bulb has to turn on immediately
when current passes through it.
But I want you to commit to an answer
and put it down in the comments
so you can't say,
oh yeah I knew that was the answer,
when I tell you the answer later on.
This question actually relates to how electrical energy
get from a power plant to your home.
Unlike a battery,
the electricity in the grid
comes in the form of alternating current, or AC,
which means electrons in the power lines
are just wiggling back and forth.
They never actually go anywhere.
So, if the charges don't come from the power plant
to your home,
how does the electrical energy actually reach you?
When I used to teach this subject,
I would say that power lines
are like this flexible plastic tubing
and the electrons inside are like this chain.
So, what a power station does,
is it pushes and pulls the electrons back and forth
60 times a second.
Now, at your house,
you can plug in a device, like a toaster,
which essentially means
allowing the electrons to run through it.
So when the power station pushes and pulls the electrons,
well, they encounter resistance in the toaster element,
and they dissipate their energy as heat,
and so you can toast your bread.
Now, this is a great story,
I think it's easy to visualize,
and I think my students understood it.
The only problem is, it's wrong.
For one thing,
there is no continuous conducting wire
that runs all the way from a power station to your house.
No, there are physical gaps,
there are breaks in the line,
like in transformers
where one coil of wire is wrapped on one side,
a different coil of wire is wrapped on the other side.
So, electrons cannot possibly flow
from one the other.
Plus, if it's the electrons
that are carrying the energy
from the power station to your device,
then when those same electrons
flow back to the power station,
why are they not also carrying energy
back from your house to the power station?
If the flow of current is two ways,
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