DENJIRO: This is a neodymium magnet that has a very strong magnetic force. Watch this. It's very strong. I'll show you a magical phenomenon using this magnet.
This is a copper plate. It's very thick with a thickness of at least 3 cm. Let's drop the neodymium magnet onto this plate. Watch carefully.
GIRL: It moved in a strange way!
DENJIRO: It looks as if the magnet suddenly decelerates right before landing. Mysterious, isn't it? Why is this happening? When the neodymium magnet gets close to the copper plate, an electric current flows inside the plate. This current is called an eddy current. The current produces a magnetic force that repels the magnetic force of the neodymium magnet. That's what causes the magnet to quickly decelerate and fall slowly.
This is already quite mysterious, but this is just the beginning. We cool the copper plate with liquid nitrogen at -196 degrees Celsius. When I drop the neodymium magnet on the plate...
GIRL: The magnet floated in air!
DENJIRO: You can also do something like this. When you cool a metal, its electrical resistance decreases, and electricity flows more easily. When the strong magnet approaches the cooled copper plate, more electricity flows in it since its electrical resistance has decreased. As a result, the magnetic force produced by the copper plate gets stronger and repels the falling magnet more.
Now I'll prove to you that electricity flows more easily when metal is cooled. Here's a power source. Here, we have a copper wire coil that is wrapped many times. It is connected to a light bulb. When I turn on the switch, the light turns on. But it's dim. So, we're going to put this copper wire into liquid nitrogen to cool it. Then lo and behold...
GIRL: It’s brighter!
DENJIRO: The light got brighter. Cooling the copper coil decreased its electric resistance and allowed electric current to flow more easily. Therefore, the light got brighter.
I hope energy will bring you all happiness. Our magic word is "Happy Energy!"
28 авг 2024
