The amazing gravity-defying superconductor

Transcript

[Music] when you switch on a small torch electricity flows from the batteries or dry cells through the metal strip or wire to the globe and then back to the batteries again the metal strip or wire is said to be a conductor because it allows electricity to pass through it however it doesn't go straight through the metal offers some resistance now that's not always a bad thing because the filament of the globe is a metal and by offering resistance it gets very hot it glows it gives out light energy so that's a good thing but sometimes resistance can be a bit of a nuisance some materials are very good conductors indeed have a look at this that's a little dark colored disc it's actually made of several things it's made from barium and copper and another element called etrium and those things have been put together in a special way in a furnace and it's made into a little ceramic disc in other words it's very much in some ways like other ceramic things that you might think of china for example that ceramics as well doesn't look very special now does it i'll put it in that tiny little dish which i've made by cutting the bottom of a coffee cup off it's made of foam plastic and then i'll place on top of that a little magnet now to show that it is a magnet let me take these metal tweezers and you'll see that it's a very powerful magnet indeed so i'll take that magnet and just sit it on top of our ceramic disc nothing special happens at all at this point however if i lower the temperature of the ceramic down down down down down something quite unusual will occur to change the temperature i'm going to use the same stuff that we used at the beginning of the program you remember that liquid nitrogen is at a temperature of about minus 196 degrees celsius that's why i'm wearing protective gloves and glasses i have some liquid nitrogen in this coffee cup and i'm going to pour this in around the ceramic disc there it is look at that bubbling away now watch that little magnet carefully because as the ceramic's temperature gets lower and lower it does some funny things it becomes a superconductor in other words if we passed electricity through it it would offer no resistance at all but also it does something else it acts in a strange way towards magnetic fields now that little rectangular thing on top that strong magnet is giving out a magnetic field and look what's happening now the disc below it is starting to repel that magnetic field and the whole thing floats up in the air that little magnet this is sometimes called the meissner effect and if you think that it's being held there by strings have a look at this i'll take a little piece of cardboard i can pass it right underneath and you can see that it's just sitting there apparently defying gravity this effect is sometimes called levitation watch what happens if i push with the end of this pin push it down let's just push back if i push it over to one side it just seems to spin around i'll take a pencil point and give it quite a hard flick on one side and it just spins apparently offering no resistance at all you are observing one of the most remarkable scientific recovery discoveries of the 20th century the meissner effect and it's all to do with superconductors and think of some of the applications that we may see of this effect in years to come we may see levitation trains in which the rails are made of ceramic materials like this and little magnets underneath the train uh enable it to just skim along without anything touching or scraping on anything at all they may be able to travel very fast indeed also superconductors are going to help us to come up with new instruments for medical research new equipment for geological exploration and also more powerful computers in the years to come you are certainly going to hear a lot more about these superconductors [Music]