RC

# Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic flux fields occurring in certain materials (superconductors) when cooled below a characteristic critical temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state.

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welcome to our second example video. Looking at super conductivity in this video, we're going to look at the energy gap for lead that we just observed, and we're going to use that to calculate what is the critical temperature. Remember, this is the critical temperature for an energy gap. AT T equals zero. So the fundamental assumption here is that we measure the energy gap at as close to zero kelvin as we possibly can get. We can't actually get all the way there, but we can get pretty close now, having established this, then we can say the energy gap would have to be equal to 3.53 This is just a constant multiplied by K, which is bolts mons, constant times the critical temperature solving for this and again being careful that we get the right units here. K is generally given and units of jewels per Calvin, and we want to make sure that we are getting into the right units in the top and the bottom. So we come up with Kelvin and not some other ratio here. So we convert Evie into jewels. So we have jewels divided by Jules Per Calvin giving us the result of 8.97 Kelvin, as are critical temperature. You can see this is an extremely low temperature, and that's this generically true for many superconductors. But as I mentioned in the previous video, there are different types of superconductors that operate with different mechanisms. And it turns out that some of those a superconductors air known as what is called high temperature superconductors or H ts CS h ts CS can operate closer to, say, 80 or 90 Calvin. In fact, there's even reports out there that people have found room temperature superconductors, which would be a game changer. Indeed, if it turns out to be, uh, riel, though these reports are all on verified, so we'll find out if this actually happens. Um, but for the time being will have to be satisfied with our other high temperature superconductors. Around 80 to 90 Calvin and with our standard superconductors down in the range of 10 Kelvin

RC
University of North Carolina at Chapel Hill

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