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  • Let's switch it on. Let's see what it does.

  • Through this coil of thick wire, we're about to pass a huge alternating electric current.

  • On top is a 1 kg aluminium plate.

  • So we hear that noise. What's that noise?

  • It's the vibration of the plate, because it's vibrating at two times the frequency of this

  • one.

  • Woah!

  • Woooaaaahhhhhhh!!

  • hahaha, how does it do that?

  • It's magical

  • To find out, I've come to the place where it all started - The Royal Institution in

  • London

  • This is the key to Faraday's magnetic lab.

  • It's amazing that the lock still works.

  • From the 1870's on this became a store room, which is why it survived and it survived intact,

  • all the joinery giant electromagnet are exactly the same as Faraday left it.

  • So this is exactly as Faraday would have had it.

  • That's right, yup.

  • In Faraday's time it was known that electric current creates a magnetic field, but it remained

  • an open question whether the reverse is possible -- if a magnetic field could generate electric

  • current.

  • Faraday answered this question with his most famous apparatus.

  • Faraday's electromagnetic induction ring. Which is this.

  • In August, 1831 Faraday wrapped two coils of insulated wire around this iron ring.

  • But in 1831 you could not go down to your local electrical hardware shop and ask for

  • x hundred meters of insulated wire, you had to insulate the wire as you went. So as you

  • pushed and pulled the wire in and out of the ring you had to insulate it. It takes 10 working

  • days, which was a huge investment of time.

  • But the investment paid off. When Faraday connected a battery to one of the coils, he

  • saw a brief pulse of current in the other coil. And when he disconnected the battery,

  • he saw a pulse of current in the other direction.

  • He realized that current was induced in the second coil only when the magnetic field through

  • it was changing.

  • And if they hadn't been wrapped on the same ring, Faraday may have noticed that the two

  • coils repel each other when the current is induced and that's due to the interaction

  • of their magnetic fields.

  • Which brings us back to this. Through the bottom coil we are passing a huge electric

  • current: 800A which alternates in direction 900 times per second. This ensures there will

  • always be a changing magnetic field above the coil.

  • Instead of a second coil we're using the Aluminium plate, but the principle is the same, the

  • changing magnetic field induces currents in the plate that create an opposing magnetic

  • field -- so it levitates.

  • How awesome is that?!

  • This current is not only good for levitating the plate. It can also make lightbulbs glow.

  • A gift. Uh, thank you. Oh.

  • That is cool. Not too close because it will burn the lamps.

  • Can I put it there? Yeah.

  • And just as current in a toaster element heats it up, the induced current in the plate dissipates

  • its energy as heat.

  • And some water too Thank you.

  • Yeah to see the temperature. Check out how hot this plate is. Oh, that

  • is nuts!

  • Is this your favorite demo? It's a flying BBQ or something

  • Tell me this is not the best dinner table centerpiece. It levitates, gives you light,

  • and you can cook on it. and all the while you're demonstrating Faraday's Law of electromagnetic

  • induction.

Let's switch it on. Let's see what it does.


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B2 中上級

跳ね上げ式バーベキュー!電磁誘導 (Levitating Barbecue! Electromagnetic Induction)

  • 39 2
    田立瑋 に公開 2021 年 01 月 14 日