I should add that superconductors can break down in high fields, but I also put it far from the coils so the field was weaker and it still acted similar to steel. This is a YCBO superconductor so the breakdown field should be pretty high. Also I should add that there are more mechanisms that cause resistance in the superconductor in AC fields. Not just the skin effect. I am learning that superconductors aren't so super in AC fields.
@@Call_Upon_YAH okay... does jesus love mario kart and summoner duel or something? I know it's not an issue but I see no reason for channel to contain video games and quote religious stuff at same time but does not upload anything related to it
Good to mention. Especially for these polycrystalline pucks, these critical fields are especially high. Agree that is not really a problem here, see my other comment for what I believe is.
I really liked how you showed the part where you got an unexpected result. It would have been easy to edit that out and have the right answer from the beginning and still explain the experiment well. However, that would miss a critical part of the scientific process, which is encountering and trying to understand unexpected results. :)
Science is less about the ‘Eureka!’ And more about the ‘Hmm, that’s interesting…’ Yes, there are eureka moments, but it’s the unexpected outcome that gets you to look at things more closely, specifically when what’s happening is outside expectations.
This is what makes him and other youtubers different from our science teachers. Teachers make us learn and cram things while youtubers explain and understand with experimentation and uncertainity.
@@DragonOfTheMortalKombat well, that’s a bit of a generalization. I bet if you ask a teacher stuff after class, there’s enthusiasm to be found. In class though, all IQs need to get to a certain test result.
The experiment was literally to see what would happen. Editing out the unexpected result would have made showing the experiment pointless and the video shorter.
Superconductors are only superconducting at DC. At AC the momentum of the superconducting electrons causes them to lag a little bit, allowing some of the electric field to penetrate. This penetrating field causes the non-superconducting electrons, which are also present, to create a non-superconducting current and lose energy through resistance. At higher frequency, this lag is more pronounced, and more of the electric field penetrates.
I couldn't find any information on how much resistance this creates. I wonder what percentage is from the penetrating field vs skin effect. Skin effect could be quite significant in the type 2 superconductor due to the fields around each imperfection.
@@TheActionLab There is also a maximum amount of current density that a superconductor can handle before it becomes a resistive load to any further current. I suspect this is what happened. This is why MRI machines have to be very carefully ramped up slowly
@@TheActionLab There's a simple proof of this -- although it doesn't tell you /how much/ at the experimental conditions. Simply consider this one fact: The block doesn't become shiny when cooled. Now, optical and LF waves are quite different; indeed, quantum effects are involved, for superconductors even around far IR. But it remains the case -- and it will be true between both classical and quantum cases (and thus LF to optical), that, at low frequencies, resistance approaches zero, while at optical, it's quite nonzero (black -- absorptive). In fact, your magnet demo at the start, hints at the nature of this effect! In the same way that ferromagnetic materials exhibit magnetic hysteresis loss (energy dissipation upon field change), type 2 superconductors exhibit conductive hysteresis loss (flux pinning). Work is done (you can feel it when you push the magnet into place!) deforming the superconducting path and trapping those flux tubes. It stands to reason, if this is simply done faster -- indeed, a couple ten thousand times a second, say by a few hundred amperes through a coil -- the material will heat up. There are other effects, I think, and also less well understood effects -- even for very pure and cold superconductors -- but this is a very hand-waving introduction to actually a very deep truth: namely, that there must be continuity in the impedance, from DC to (literally) light. The fact that it superconducts at DC, isn't actually much of a guarantee of behavior at AC; but the fact that it's not shiny at optical frequencies, is a guarantee that -- somewhere inbetween -- it will be lossy. The best AC superconductors I'm aware of (and it's been a while since I looked, but probably is still relevant) are made of spun niobium (type 1, no flux pinning), cooled to 2.2K or so, with a Q factor in the 10^8 range -- better than quartz crystal resonators, but still not infinite -- operating at 500MHz or so. These are used in particle accelerators, basically because the bunches of particles have very little charge, macroscopically speaking, so they couple to the applied fields very weakly, and thus require a large multiplication ratio (Q factor) to drive effectively.
I love induction heaters, definitely got a "kid with a magnifying glass" feel with them. Especially cool are the really strong ones that get something so hot they can melt it, but can also magnetically levitate the molten material inside it... that is until you turn the power off and then watch out... that's something the Backyard Scientist would wearing shorts and flip flops.
@@HeyChickens Reminds me of an EOD guy that had to detonate a suspicious package that was near the barracks when I was in the military.. he carried a brick of c4 to the package wearing shorts, sandals, a t-shirt, backwards baseball cap.. and a kevlar vest... lol. Like.. really? Why, just why? haha.. (because regulations say you need to wear a minimum of a kevlar vest).
This one little experiment illustrates the important difference between theory and observation. It's easy to arrive at conclusions based on logic but we always need to make sure there isn't some variable that was missed in the train of thought. Great video!
@@AdityaMehendale Oh, that was a generic reference to ideas we have about things. But the natural conclusion in the case of this video is that a superconductor should not heat up at all through induction since they have zero resistance. This experiment clearly shows that the conclusion was mistaken. It serves as a great example of how we can take things for granted
I am sorry, but the statement "This one little experiment illustrates the important difference between theory and observation." is fundamentally wrong. A scientific theory is at the highest level of rigorous understanding of the physical world. It has explained all of past experiments and current state of the world and it can also make predictions about future experiments. If an experiment defies an established theory, the theory would be thrown out and a more refined/correct version would be put in its place. In this situation, the theory perfectly predicts what has been observed. There is nothing against theory here and no surprise at the scientific level. What you should actually say is that: "The observation went against MY expectation because I was not fully aware of the depth of superconductivity theory". Nothing more can be said here.
The main effect here are AC losses inside the superconductor, not the penetration depth. The constantly changing field is constantly getting pushed in and out of the superconductor. Specfically, the 'pinned' fluxes are moved around a lot. This costs a relatively huge amount of energy. It is also one of the biggest, if not THE biggest, issue in making superconductors usable in practical applications. Also your puck of ReBCO is bulk polycrystalline. This is great for flux pinning (which is why it's used for these pucks) due to the very high amount of grain boundaries. But in this situation it works against you, as it costs even more energy to move these fluxes around. Even more of an issue is that these grain boundaries are normal conducting, and with a very high resistance at that. You're trying to induce huge currents in something with a terrible transport current capacity. For more information, you might want to look into topics like these AC losses in superconductors and the Bean critical state model. As a sidenote: your steel penny might also heat up so much more because it is ferromagnetic
Yes, but what are the AC losses? It has to translate into actual resistance in the superconductor. The magnetic fields that are allowed to penetrate this type 2 superconductor also have a skin depth around each imperfection. So isn't that the same as saying it is due to the resistance from the skin depth?
@@TheActionLab It does have to do with a penetration field, but not specifically this skin depth effect. That effect is there don't get me wrong, but it's not the main reason for the loss of energy. You have to think how the superconductor gets magnetized "up and down" all the time. This is called magnetization losses or hysteresis losses. Another AC loss type that happens here are coupling losses, due to current moving between strands or grains of superconductor, so through normal material.
Also about the steel penny, I don't think that hysteresis losses (from being ferromagnetic) from the steel penny are the main reason for the heating. I think it is a mainly due to the eddy currents with high resistance. Even at high temps above the curie temps the iron heats very quickly.
@@TheActionLab Absolutely! AC effects is the root of many of ours problems working with applied superconductivity. As for the penny, that's a good point. Would have to compare some numbers then to know for sure. I do know some induction cooking pans work better than other due to their stronger magnetic properties. But maybe the effect of frequency is different in those appliances.
👍 good vid. Another interesting aspect of superconductors is they contain "normal" non-superconducting electrons, but the effect of the normal electrons is not observed in DC currents and magnetic fields because the superconducting electrons "short-out" any E-fields that might be produced. However, at AC frequencies the short-out effect is never quite perfect, and normal electrons get to respond and lose energy in the process.
Sheeesh! You have all the fun tools and experiments. I appreciate that you explain details like regular conductor and superconductor. Definitely makes your videos more enjoyable to watch!
Now that you explained it and I think about it, it makes sense. A superconductor can have zero ohms as long as the electricity we are passing through it has ANY straight path to get from one side to the other. However, that doesn't mean that the entire block of material has zero ohms. There can easily be some areas with higher resistance due to imperfections in the material, but those imperfections won't raise the resistance, since the electricity automatically looks for the path of least resistance. But when that electricity is being generated by tiny eddy currents all throughout the material, it is much more likely to get trapped between some of the imperfections and be forced to flow through a portion of the material that isn't quite a superconductor. This is my hypothesis anyways. Someone please correct me if I'm wrong.
Love this channel. I've seen the shorts a million times but only today did I actually subscribe. It's nice to see something so educational can do so well in YT.
I believe superconductors also will stop superconducting if they're are exposed to too high a magnetic field along with the field changing too quickly. Not sure how strong the field is here though.
This! The limiting amount for a good super conductor is about 0.1 Tesla at 0K. With the amount decreasing with temperature. Unless he's using YBCO which can do 120+ tesla
This is a YBCO superconductor. Also I removed the superconductor from the center and put it farther from the field and still easily boiled the LN2 in a weaker field. It didn't seem like the field was too strong.
@@madlad5199 probably generating likes and impressions with less "reports" before the channel is renamed and used for different botting... I've noticed a lot of these lately. even some just saying "whomever sees this I hope you have a wonderful blessed day" and they come up right after a video is posted, so they aren't authentic people.
Unless the penny you used was old (before 1982) it is copper-plated zinc, which has a much higher resistance than copper. It didn't get hot because it had too much internal resistance. Try a copper (pre-1982) penny and it will probably get hotter faster than the steel penny.
I came into the comments to say this exact same thing. The penny he used is defiantly a newer one based on the union shield side of the penny. This means that the penny used was 2010 or newer so defiantly coper-plated zinc making it more zinc than copper.
@@vintilk I hope he sees this and re[eats the experiment with a copper penny. As far as the superconductor caused boiling, there are probably some experiments that can better explain that action, too. It would be nice if the RF filed could be adjusted to see if there was a non-linear point that would help explain the results.
We don't know the frequency of the induction heater, but they tend to be around 100kHz, which (google...) should mean about 100u skin depth. And the copper on that penny is only (google...) 20u, so yeah, I'm pretty sure that was mostly a zinc penny in that test.
Came to to comments to see if anybody pointed out 'recent' 1 cent pieces are primarily zinc because copper is too expensive. Also heard that zinc "fumes" (heating, burning, vapor, etc.) is on the toxic side and should be avoided, but don't know the specifics of this myself.
Another reason may be that not everything in that puck is superconducting. YBCO is AFAIK made by sintering, and it's possible that there's a mix of superconductor and "loose oxides" for lack of a better term. For magnetic levitation only the superconducting parts are relevant. The rest of the stuff might be magnetically inert, but in the induction heater the non-superconducting parts might heat up.
James, your channel is awesome. The combination of broad knowledge in the physical sciences and childlike curiosity is a winning combination. Plus, you show a moment where something unexpected happened - not very common in a science video. Love it.
I believe that the reason the steel penny generated more heat is mainly because there is greater magnetic flux in the steel than in the copper. Same as why we use iron in the cores of transformers. That is why you can only use ferromagnetic pans on induction stoves, in principle you could use a copper or aluminum pan, but the efficiency would be much lower.
You are talking about magnetic hysteresis losses. In ferromagnetic materials some heat is generated due to the magnetic domains alternating. But eddy current heat due to the resistance in iron is much more significant than the hysteresis heat created. You can see this is true because even at high temperatures (above curie temps where there are no more magnetic domains) the iron will still heat up faster than copper.
Pretty sure its because Super conductors have a limit amount of current /magnetic feild till it just becomes a metal again. Super conductors work because electrons in a metal pair up and make cooper pairs which are fermions and cannot change momentum hence the '0' resistance. When the magnetic field or temperature is too high they sort of go through a quantum phase transformation and revert into transferring current the normal way.
@@WouterVerbruggen yeah but at super low temperatures its metallic state. I don't see its transformation into a ceramic being the limiting factor over the super conductor transition temperature
The thing I love most about your channel is you ask the same questions I ask. The difference is, you have an induction heater and a super conductor. .... I only have an induction heater and it doesn't work
Nice research! Most youtuber gloss over something like this as an error, but I love that you took the time to nail down what must be going on. Respect!
*The superconductor will levitate.* Or it could. That was my instant response to the title question. But that depends on the induction coil being underneath the superconductor.
About the steel vs aluminum it's not about the conductivity but rather thanks to the iron magnetic hysteresis, each time the field changes, magnetic domains are following it and it dissipates a lot of energy, more than eddy current with iron. That's why iron/nickel beat all metals in induction, way before copper/silver (good conductors) and tin/lead (bad conductors). Out of this phenomenon, I think the conductivity increases the effet: the voltage is fixed and corresponds to a 1 turn "transformer" secondary. When the conductivity is higher, the current is higher so it makes more heating power. The device source is current limited so you don't see big difference but if it wasn't, copper would beat lead !
More about resistivity versus what the coil is made of, and a geometry factor. When their resistivities are similar (or, indeed if the coil's is worse than the work's), efficiency is crap and you're doing a whole lot of work for not a lot of heat. You simply get less heat (and other effects like Lorentz force) when it's, say, titanium (coil) on titanium (work), than when it's copper on aluminum, or copper on steel. Or indeed, copper on copper, which maximizes Lorentz force per watt, you could say. (With respect to a given voltage input, say.) Higher resistivity isn't really a problem, to a point -- as long as the workpiece is thick enough to absorb all the applied field (i.e. several skin depths thick). Titanium and graphite for example heat very nicely, despite being fair resistors in comparison to copper or even (pure) iron. Obviously, resistivity can't be too high, else it simply doesn't absorb enough field to matter -- hence why glass, or plastic, or, well, LN2 for that matter, doesn't heat up appreciably (skin depth is almost infinite in them!). And conversely, a thin conductive layer (shallow skin depth) isn't a problem per se -- copper is quite shallow but works very well as a coil. Iron works quite poorly, but its magnetic permeability is making the skin hundreds of times shallower than for an equivalent nonmagnetic material. Superconductors have indeed a microscopic layer, but as long as critical field isn't exceeded in it, that's fine as well. (The geometry factor is basically just to say: you can always make a worse coil. For example, by placing it completely beside the work itself, so they don't couple at all. That's a pretty awful geometry, you'll agree. 😆)
Interesting, learned something new about superconductors, I wonder how that would effect a quantum computer's communication. Would you have the same effect with a collapsing field of on, off, on? BTW was the man bunn always there?
could there be an effect from vibrations at the same frequency as the current? or would this be neglegible? What I´m thinking is that if current was in one direction, the superconductor would want to float or spin (as they do when they levitate) but since you flip the current, they would sink or rotate the other direction. Would these switches(i.e. vibration) do anything?
In a way less, what's getting pushed/vibrated around are the magnetic field "fluxes" inside the superconductor (as mentioned also by James) which costs a lot of energy.
Huh, that "copper" penny is *mostly* zinc: only the skin is copper. But this is an AC field... Did you do the math how deep the field would go at that frequency and how much of the interaction would be copper vs zinc?
@@timk5867 1982 pennies don't have that obverse side (it would have the Lincoln memorial.) I can't quite make out the date on this one, but I believe it to be at least 2010 because of the design on the back.
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The heating is not caused only by resistive propriety of the material but also because of the magnetic proprieties. Magnetic dipoles in the material oscillates according to the changing magnetic field and this cause heating
Good science trying just the LN2. LN2 being affected and the superconductor being affected would both be weird results on the surface. I had correctly guessed that the superconductor exhibited more resistance than expected, but the LN2 still had to be ruled out to be sure.
.. we call this an induction stove - and it can be bought in any store for electric supplies .. we have been using that for over 10 years in our kitchen .. (pretty neat, as it has a glas surface)
The induced curent is equal to voltage divided by resistance according to ohms law. Meaning lower resistance will heat more. The copper penny probably heats less because its mostly zinc and not really copper.
My soldering iron is induction. There is a small coil in the end of each tip and the core of the tip is different alloys depending on the temp of the tip you select.
Hi. I have been watching and subbed to your shorts forever. I just found this channel today. I want to tell you I've Keane so much about science just from watching your channel. You make it so fun & interesting. I didn't pay much attention in school and have been left questioning a lot of things happening in the world. You explain a whole lot. Thank you. ❤️
It should be added that ferromagnetic materials will also experience a heating effect from magnetisation hysteresis losses. They get magnetised by the field from the coils. Every time the magnetisation switches, some heat is generated. This effect is usually much stronger than the heating from eddy currents. That's why only steel pots work on induction hobs.
This is really interesting and I'd like to understand it more. First, I think we need to understand how the temperature of the solid gets increased. I guess the main process is electrons inelastically scattering off the lattice and transferring their energy to the lattice. If we calcualte the temperature of the electrons (here "temperature" basically means kinetic energy), it will be huge. The temperature we are feeling is actually the temperature of the lattice. (I guess this is not contradictory because electrons have a much smaller heat capacity than the lattice.) Therefore, the heating effect we get by the electric current is actually of a different mechanism than zero resistivity, which concerns the interaction between electrons and disorder. The disorder scattering is typically assumed to be elastic so I guess it doesn't play a role in the heating. Then, the heating will happen as long as we have a current so the situation should be similar to that of a normal metal. However, I believe the material you are using is an insulator, so actually the real interesting thing the superconductivity is doing is to induce a current (the Meissner effect induced a current to keep the magnetic field constant). I guess we always use some kind of metal to do induction heating but by virtue of superconductivity we can use an insulator to do it. I love superconductors and would love to see more vidoes about them. Thanks.
Amazing experience, however, there is another reason for induction heating effect besides the skin depth, ur YBCO is not a single crystal disk and magnetic field induce heating through grains via boundary interaction and crystal defects.
I think I read somewhere that the reason superconductor locks magnet in place is due to the imperfection with induce eddy currents , although I am not sure if it matters , I want know if it has some significance
The imperfections in type 2 superconductors allow the magnetic field to penetrate it (this allows the quantum locking) but it doesn't change the fact that there is 0 resistance inside the conductor. But it does mean that the skin effect is also surrounding the imperfections. So a type 2 superconductor would have worse skin effect than a type 1 superconductor.
I am wondering that the frequency of the current applied into the induction coil depends on the power supply you use. That means, when you turn on and off the switch, there is a step change that changes the frequency profile of the applied current unless the power supply has a mechanism to regulate these spikes and harmonics. In my opinion, these high frequency noises and harmonics may have very low averaged amplitude; but may be enough to penetrate the very thin skin depth of the superconductor. This may not be a big deal unless the experiment requires to find the change in boiling temperature as a function of frequency.
I have the answer as I make superconducting pucks. The superconductor layer is very thin (less than a human hair in thickness) so it is in a sandwich of stainless steel and copper. In addition these ribbons are soldered together more than likely to add up to the diameter so this would introduce tin and maybe lead. The ultimate experiment would be to use a single domain chunk of YBCO or some BSCCO superconductor. I've actually done a similar experiment with putting a chunk of YCBO in the microwave. When warm it sparks but under liquid nitrogen it does nothing! I made a video but never posted because I wasn't happy with my camera set up so .... feel free to try it! (with a chunk of pure)
Interesting I've only seen these pucks as powered ReBCO compressed in a mold instead of proper crystalline tape stacks. It would change the electrodynamics of the situation quite a bit, coupling losses would be much more significant. Wouldn't expect it to work as well as a "quantum locking" demonstrator then though.
It can partially also be because of the fact that nothing can be a perfect conductor even superconductors have some resistance which is very less than the resistance of normal conductors but still it is more than 0 resistance.
3:58 I think the supeconductor will heat up. The eddy currents will still happen after all, and will keep changing direction. This will dump some energy into the superconductor.
I would like to see 2 more test if your up for it. 1. Put a magnet in a cup of water in the coil to see if it heats up. 2. Raise the induction coil to a height where you can have the superconductor levitate the magnet below the cup and coil while turning on the induction coil to see if it drops the magnet or does something different.
I think this superconductor mostly consists of a superconductive phase which is continuous throughout the sample with small inclusions of non-superconductive phase and it is responsible for heating up the sample
I really was surprised by what occurred with the superconductor. I expected it to ignore the alternating magnetic fields until it warmed up some, then it would react more and more. But, even when you refroze the superconductor it still had a reaction when I assumed it wouldn't. I don't know if you were pretending to be surprised or really surprised, but I really was. I didn't know that superconductors has a penetration depth even when cooled or the other mechanisms you were starting to allude to in your pinned comment. Very interesting stuff!
Is it because you just heating the metal and the superconductor and the temperature of the liquid nitrogen increase, so it wants to evaporate faster. The opposite of cooling down and stop boiling. Is the answer that simple?
Are there imperfections or surface effects on the superconductor? Like, localized impurities at the surface? Edit: aaaand sort of yes. It was a surface effect after all.
It's not all THAT efficient -- the coil is water cooled with good reason! Typical for a furnace might be 70%, which is still quite a lot better than gas-fired though.
High frequency dissipation in superconductors is covered in the Michael Tinkham book (Introduction to Superconductivity) chapter 2.5.2 - there's a rather elegant and simple description there. In essence, even in the superconducting state, not all electrons are part of the superfluid (unless you are at absolute zero, which is unattainable anyways). Under a DC current, the "super" electrons will short circuit the coexisting normal electrons, giving zero resistance and zero DC heating. Yet under an AC current, the "super" electrons will no longer be able to fully screen out the electric field, and the rest normal electrons will be dragged around by the applied field - although at a reduced intensity - and dissipate energy in the form of heat. This is also the reason why there is still loss in superconducting cavities for microwave applications (such as quantum computing). As a visual demonstration, it'd be fun to dial the frequency of your inductive heater, and monitor how the boiling rate changes!
Another nuance here is the YBCO used, which means you have a type-II superconductor. The lower critical field of YBCO is actually quite low at only 0.01-0.05 Tesla level. This means you may as well get superconducting vortices (very tiny though) consisting of normal electrons in them. Under an AC current, this creates a lot of superconducting-normal electron boundaries, which can be another source of dissipation.
I should add that superconductors can break down in high fields, but I also put it far from the coils so the field was weaker and it still acted similar to steel. This is a YCBO superconductor so the breakdown field should be pretty high. Also I should add that there are more mechanisms that cause resistance in the superconductor in AC fields. Not just the skin effect. I am learning that superconductors aren't so super in AC fields.
@@Call_Upon_YAH okay... does jesus love mario kart and summoner duel or something? I know it's not an issue but I see no reason for channel to contain video games and quote religious stuff at same time but does not upload anything related to it
The irony of posting this on a science channel.
Good to mention. Especially for these polycrystalline pucks, these critical fields are especially high. Agree that is not really a problem here, see my other comment for what I believe is.
I’m curious to see it react w/o the liquid nitrogen 😱🤷🏻♂️. Curiosity kills tho eh? Lol
Cool. Please, make the same experiment with DC current for comparison.
I really liked how you showed the part where you got an unexpected result. It would have been easy to edit that out and have the right answer from the beginning and still explain the experiment well. However, that would miss a critical part of the scientific process, which is encountering and trying to understand unexpected results. :)
Completely agree!
Science is less about the ‘Eureka!’ And more about the ‘Hmm, that’s interesting…’
Yes, there are eureka moments, but it’s the unexpected outcome that gets you to look at things more closely, specifically when what’s happening is outside expectations.
This is what makes him and other youtubers different from our science teachers. Teachers make us learn and cram things while youtubers explain and understand with experimentation and uncertainity.
@@DragonOfTheMortalKombat well, that’s a bit of a generalization. I bet if you ask a teacher stuff after class, there’s enthusiasm to be found.
In class though, all IQs need to get to a certain test result.
The experiment was literally to see what would happen. Editing out the unexpected result would have made showing the experiment pointless and the video shorter.
Superconductors are only superconducting at DC. At AC the momentum of the superconducting electrons causes them to lag a little bit, allowing some of the electric field to penetrate. This penetrating field causes the non-superconducting electrons, which are also present, to create a non-superconducting current and lose energy through resistance.
At higher frequency, this lag is more pronounced, and more of the electric field penetrates.
I couldn't find any information on how much resistance this creates. I wonder what percentage is from the penetrating field vs skin effect. Skin effect could be quite significant in the type 2 superconductor due to the fields around each imperfection.
@@TheActionLab Also, wouldn't the resistance go up when the skin layer is heated since it will heat the neighboring parts slightly?
@@TheActionLab There is also a maximum amount of current density that a superconductor can handle before it becomes a resistive load to any further current. I suspect this is what happened. This is why MRI machines have to be very carefully ramped up slowly
@@TheActionLab There's a simple proof of this -- although it doesn't tell you /how much/ at the experimental conditions. Simply consider this one fact:
The block doesn't become shiny when cooled.
Now, optical and LF waves are quite different; indeed, quantum effects are involved, for superconductors even around far IR. But it remains the case -- and it will be true between both classical and quantum cases (and thus LF to optical), that, at low frequencies, resistance approaches zero, while at optical, it's quite nonzero (black -- absorptive).
In fact, your magnet demo at the start, hints at the nature of this effect!
In the same way that ferromagnetic materials exhibit magnetic hysteresis loss (energy dissipation upon field change), type 2 superconductors exhibit conductive hysteresis loss (flux pinning). Work is done (you can feel it when you push the magnet into place!) deforming the superconducting path and trapping those flux tubes.
It stands to reason, if this is simply done faster -- indeed, a couple ten thousand times a second, say by a few hundred amperes through a coil -- the material will heat up.
There are other effects, I think, and also less well understood effects -- even for very pure and cold superconductors -- but this is a very hand-waving introduction to actually a very deep truth: namely, that there must be continuity in the impedance, from DC to (literally) light. The fact that it superconducts at DC, isn't actually much of a guarantee of behavior at AC; but the fact that it's not shiny at optical frequencies, is a guarantee that -- somewhere inbetween -- it will be lossy.
The best AC superconductors I'm aware of (and it's been a while since I looked, but probably is still relevant) are made of spun niobium (type 1, no flux pinning), cooled to 2.2K or so, with a Q factor in the 10^8 range -- better than quartz crystal resonators, but still not infinite -- operating at 500MHz or so. These are used in particle accelerators, basically because the bunches of particles have very little charge, macroscopically speaking, so they couple to the applied fields very weakly, and thus require a large multiplication ratio (Q factor) to drive effectively.
@@TheActionLab You should hook the superconductor up to an Oscilloscope and measure the frequency respone. Should be interesting.
I love induction heaters, definitely got a "kid with a magnifying glass" feel with them. Especially cool are the really strong ones that get something so hot they can melt it, but can also magnetically levitate the molten material inside it... that is until you turn the power off and then watch out... that's something the Backyard Scientist would wearing shorts and flip flops.
Safety shorts and safety flip flops!
He wore glasses, that's protect you right?
@@gallium-gonzollium Genius idea from stuff made here
@@Derekzparty Hilarious comment dude! Lol
@@HeyChickens Reminds me of an EOD guy that had to detonate a suspicious package that was near the barracks when I was in the military.. he carried a brick of c4 to the package wearing shorts, sandals, a t-shirt, backwards baseball cap.. and a kevlar vest... lol. Like.. really? Why, just why? haha.. (because regulations say you need to wear a minimum of a kevlar vest).
This one little experiment illustrates the important difference between theory and observation. It's easy to arrive at conclusions based on logic but we always need to make sure there isn't some variable that was missed in the train of thought. Great video!
I'm curious to know - what was your initial "conclusion based on logic"?
@@AdityaMehendale Oh, that was a generic reference to ideas we have about things. But the natural conclusion in the case of this video is that a superconductor should not heat up at all through induction since they have zero resistance. This experiment clearly shows that the conclusion was mistaken. It serves as a great example of how we can take things for granted
@@jacobopstad5483 I had expected the SC to "jump out of" the LN beaker when the coil was switched-on.
I am sorry, but the statement "This one little experiment illustrates the important difference between theory and observation." is fundamentally wrong. A scientific theory is at the highest level of rigorous understanding of the physical world. It has explained all of past experiments and current state of the world and it can also make predictions about future experiments. If an experiment defies an established theory, the theory would be thrown out and a more refined/correct version would be put in its place.
In this situation, the theory perfectly predicts what has been observed. There is nothing against theory here and no surprise at the scientific level.
What you should actually say is that: "The observation went against MY expectation because I was not fully aware of the depth of superconductivity theory". Nothing more can be said here.
@@Thesignalpath Well said, Shahriar :) It's surreal to find you in the comments' section!
The main effect here are AC losses inside the superconductor, not the penetration depth. The constantly changing field is constantly getting pushed in and out of the superconductor. Specfically, the 'pinned' fluxes are moved around a lot. This costs a relatively huge amount of energy. It is also one of the biggest, if not THE biggest, issue in making superconductors usable in practical applications. Also your puck of ReBCO is bulk polycrystalline. This is great for flux pinning (which is why it's used for these pucks) due to the very high amount of grain boundaries. But in this situation it works against you, as it costs even more energy to move these fluxes around. Even more of an issue is that these grain boundaries are normal conducting, and with a very high resistance at that. You're trying to induce huge currents in something with a terrible transport current capacity. For more information, you might want to look into topics like these AC losses in superconductors and the Bean critical state model.
As a sidenote: your steel penny might also heat up so much more because it is ferromagnetic
Yes, but what are the AC losses? It has to translate into actual resistance in the superconductor. The magnetic fields that are allowed to penetrate this type 2 superconductor also have a skin depth around each imperfection. So isn't that the same as saying it is due to the resistance from the skin depth?
@@TheActionLab It does have to do with a penetration field, but not specifically this skin depth effect. That effect is there don't get me wrong, but it's not the main reason for the loss of energy. You have to think how the superconductor gets magnetized "up and down" all the time. This is called magnetization losses or hysteresis losses. Another AC loss type that happens here are coupling losses, due to current moving between strands or grains of superconductor, so through normal material.
@@WouterVerbruggen Yes I see there are many more mechanisms for losses. The bottom line is that superconductors are pretty lame in AC fields
Also about the steel penny, I don't think that hysteresis losses (from being ferromagnetic) from the steel penny are the main reason for the heating. I think it is a mainly due to the eddy currents with high resistance. Even at high temps above the curie temps the iron heats very quickly.
@@TheActionLab Absolutely! AC effects is the root of many of ours problems working with applied superconductivity.
As for the penny, that's a good point. Would have to compare some numbers then to know for sure. I do know some induction cooking pans work better than other due to their stronger magnetic properties. But maybe the effect of frequency is different in those appliances.
You always do experiments that I didn't know I wanted to see.
He's making you smarter every day.
He's making unknown unknowns known.
👍 good vid. Another interesting aspect of superconductors is they contain "normal" non-superconducting electrons, but the effect of the normal electrons is not observed in DC currents and magnetic fields because the superconducting electrons "short-out" any E-fields that might be produced. However, at AC frequencies the short-out effect is never quite perfect, and normal electrons get to respond and lose energy in the process.
That makes sense; thanks!
Having an unexpected result is the best part of this video. It's what science is all about.
Sheeesh! You have all the fun tools and experiments. I appreciate that you explain details like regular conductor and superconductor. Definitely makes your videos more enjoyable to watch!
an experiment i would never of thought to do, but now i really want to do it myself!
Interesting experiment! Can’t wait to see the results!
Now that you explained it and I think about it, it makes sense. A superconductor can have zero ohms as long as the electricity we are passing through it has ANY straight path to get from one side to the other. However, that doesn't mean that the entire block of material has zero ohms. There can easily be some areas with higher resistance due to imperfections in the material, but those imperfections won't raise the resistance, since the electricity automatically looks for the path of least resistance. But when that electricity is being generated by tiny eddy currents all throughout the material, it is much more likely to get trapped between some of the imperfections and be forced to flow through a portion of the material that isn't quite a superconductor. This is my hypothesis anyways. Someone please correct me if I'm wrong.
Love this channel. I've seen the shorts a million times but only today did I actually subscribe. It's nice to see something so educational can do so well in YT.
6:50 “Super conductors aren’t that super in alternating fields” well said.
I believe superconductors also will stop superconducting if they're are exposed to too high a magnetic field along with the field changing too quickly. Not sure how strong the field is here though.
This!
The limiting amount for a good super conductor is about 0.1 Tesla at 0K. With the amount decreasing with temperature. Unless he's using YBCO which can do 120+ tesla
Saturation effect. It can only hold so many lines of magnetic flux.
This is a YBCO superconductor. Also I removed the superconductor from the center and put it farther from the field and still easily boiled the LN2 in a weaker field. It didn't seem like the field was too strong.
Well, this is a new spam bot.
@@madlad5199 probably generating likes and impressions with less "reports" before the channel is renamed and used for different botting... I've noticed a lot of these lately. even some just saying "whomever sees this I hope you have a wonderful blessed day" and they come up right after a video is posted, so they aren't authentic people.
Unless the penny you used was old (before 1982) it is copper-plated zinc, which has a much higher resistance than copper. It didn't get hot because it had too much internal resistance. Try a copper (pre-1982) penny and it will probably get hotter faster than the steel penny.
I came into the comments to say this exact same thing. The penny he used is defiantly a newer one based on the union shield side of the penny. This means that the penny used was 2010 or newer so defiantly coper-plated zinc making it more zinc than copper.
@@vintilk I hope he sees this and re[eats the experiment with a copper penny. As far as the superconductor caused boiling, there are probably some experiments that can better explain that action, too. It would be nice if the RF filed could be adjusted to see if there was a non-linear point that would help explain the results.
We don't know the frequency of the induction heater, but they tend to be around 100kHz, which (google...) should mean about 100u skin depth. And the copper on that penny is only (google...) 20u, so yeah, I'm pretty sure that was mostly a zinc penny in that test.
Came to to comments to see if anybody pointed out 'recent' 1 cent pieces are primarily zinc because copper is too expensive. Also heard that zinc "fumes" (heating, burning, vapor, etc.) is on the toxic side and should be avoided, but don't know the specifics of this myself.
@@dx9s I put a small stack of pennies on the concrete floor and then aimed my propane torch at it. The pile collapsed as the zinc melted.
This is a neat explanation of some of the complexities of superconductivity in a benchtop experiment.
Another reason may be that not everything in that puck is superconducting. YBCO is AFAIK made by sintering, and it's possible that there's a mix of superconductor and "loose oxides" for lack of a better term.
For magnetic levitation only the superconducting parts are relevant. The rest of the stuff might be magnetically inert, but in the induction heater the non-superconducting parts might heat up.
James, your channel is awesome. The combination of broad knowledge in the physical sciences and childlike curiosity is a winning combination. Plus, you show a moment where something unexpected happened - not very common in a science video. Love it.
I believe that the reason the steel penny generated more heat is mainly because there is greater magnetic flux in the steel than in the copper. Same as why we use iron in the cores of transformers. That is why you can only use ferromagnetic pans on induction stoves, in principle you could use a copper or aluminum pan, but the efficiency would be much lower.
You are talking about magnetic hysteresis losses. In ferromagnetic materials some heat is generated due to the magnetic domains alternating. But eddy current heat due to the resistance in iron is much more significant than the hysteresis heat created. You can see this is true because even at high temperatures (above curie temps where there are no more magnetic domains) the iron will still heat up faster than copper.
Superb. This is one of your best experiments yet!
Thank you for this demonstration.
It will blow up probably lol😂
Hahahahhahahahhahahah so funny 🤣🤣🤣
😑😑😑😑
@@Djbuzzchannelyt who spit in your cereal?
Nah
It didn't lol
@@jiddy30 he put the milk before probably
interesting topic + to the point delivery + informative = entertaining video.. really good work..
2:09 really disappointed you didn't show more of the magnetic particles inside the coil when you activate it. That was SO freaking COOL!!
This is literally the best example of the video we didn't need but we deserved.
It would be interesting to see some experiments with sympathetic resonance
The new hairdo tho... Love watching the random stuff you get in to out in the garage, always pumped when I see a new upload in my subs
Pretty sure its because Super conductors have a limit amount of current /magnetic feild till it just becomes a metal again.
Super conductors work because electrons in a metal pair up and make cooper pairs which are fermions and cannot change momentum hence the '0' resistance.
When the magnetic field or temperature is too high they sort of go through a quantum phase transformation and revert into transferring current the normal way.
Yes, and it depends on both (and temperature as well) at the same time. Even worse, this stuff (ReBCO) is a ceramic in normal state.
@@WouterVerbruggen yeah but at super low temperatures its metallic state. I don't see its transformation into a ceramic being the limiting factor over the super conductor transition temperature
The thing I love most about your channel is you ask the same questions I ask. The difference is, you have an induction heater and a super conductor. .... I only have an induction heater and it doesn't work
Your old hair cut looked more fitting than this new style. Nice videos.
Nice research! Most youtuber gloss over something like this as an error, but I love that you took the time to nail down what must be going on. Respect!
*The superconductor will levitate.* Or it could. That was my instant response to the title question. But that depends on the induction coil being underneath the superconductor.
About the steel vs aluminum it's not about the conductivity but rather thanks to the iron magnetic hysteresis, each time the field changes, magnetic domains are following it and it dissipates a lot of energy, more than eddy current with iron. That's why iron/nickel beat all metals in induction, way before copper/silver (good conductors) and tin/lead (bad conductors).
Out of this phenomenon, I think the conductivity increases the effet: the voltage is fixed and corresponds to a 1 turn "transformer" secondary. When the conductivity is higher, the current is higher so it makes more heating power. The device source is current limited so you don't see big difference but if it wasn't, copper would beat lead !
More about resistivity versus what the coil is made of, and a geometry factor.
When their resistivities are similar (or, indeed if the coil's is worse than the work's), efficiency is crap and you're doing a whole lot of work for not a lot of heat. You simply get less heat (and other effects like Lorentz force) when it's, say, titanium (coil) on titanium (work), than when it's copper on aluminum, or copper on steel. Or indeed, copper on copper, which maximizes Lorentz force per watt, you could say. (With respect to a given voltage input, say.)
Higher resistivity isn't really a problem, to a point -- as long as the workpiece is thick enough to absorb all the applied field (i.e. several skin depths thick). Titanium and graphite for example heat very nicely, despite being fair resistors in comparison to copper or even (pure) iron. Obviously, resistivity can't be too high, else it simply doesn't absorb enough field to matter -- hence why glass, or plastic, or, well, LN2 for that matter, doesn't heat up appreciably (skin depth is almost infinite in them!).
And conversely, a thin conductive layer (shallow skin depth) isn't a problem per se -- copper is quite shallow but works very well as a coil. Iron works quite poorly, but its magnetic permeability is making the skin hundreds of times shallower than for an equivalent nonmagnetic material. Superconductors have indeed a microscopic layer, but as long as critical field isn't exceeded in it, that's fine as well.
(The geometry factor is basically just to say: you can always make a worse coil. For example, by placing it completely beside the work itself, so they don't couple at all. That's a pretty awful geometry, you'll agree. 😆)
Interesting, learned something new about superconductors, I wonder how that would effect a quantum computer's communication. Would you have the same effect with a collapsing field of on, off, on? BTW was the man bunn always there?
Just thought I’d say, I LOVE your channel and what you show us! It’s BRILLIANT👍👍🇬🇧
could there be an effect from vibrations at the same frequency as the current? or would this be neglegible? What I´m thinking is that if current was in one direction, the superconductor would want to float or spin (as they do when they levitate) but since you flip the current, they would sink or rotate the other direction. Would these switches(i.e. vibration) do anything?
In a way less, what's getting pushed/vibrated around are the magnetic field "fluxes" inside the superconductor (as mentioned also by James) which costs a lot of energy.
I was convinced no heating because no resistance. Eye opening experiment. Thanks for showing us that.
I wasn't expecting this result either and had to do some digging on why it would be happening!
@@TheActionLab I love it when science and evidence wins over beliefs and expectations. Knowing that you were also surprised meant a lot to me! 🙂
Huh, that "copper" penny is *mostly* zinc: only the skin is copper. But this is an AC field... Did you do the math how deep the field would go at that frequency and how much of the interaction would be copper vs zinc?
1982 and older pennies are copper
Mostly
German silver is not silver
@@timk5867 1982 pennies don't have that obverse side (it would have the Lincoln memorial.) I can't quite make out the date on this one, but I believe it to be at least 2010 because of the design on the back.
I feel informed. This clarified that superconduction is not so much an intrinsic material property as much as it is a statistical or structural one.
Nice
Answers to questions that I wouldn't even know who to ask.
Love this channel.
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To the newbies, you should also note that this data is worthless without an existing understanding of data analysis.
This is very correct and good.
@Alina Fischer
WASP ⬇️⬇️
Also I love how in your long videos there is so much more 'Ima press this button an see what happens' going on.
Please get a hair cut.
The heating is not caused only by resistive propriety of the material but also because of the magnetic proprieties. Magnetic dipoles in the material oscillates according to the changing magnetic field and this cause heating
Wow, did not think it would boil. Thank you for the science!
Dude the water ice building up and being deposited in the magnetic field is awesome too
I mean he's a great guy, he's in hospital but still is doing things for us Great Job brother
Ferromagnetic metals heat up more than normal conductors with the same conductivity when inside an induction heater, that's something to note.
Good science trying just the LN2. LN2 being affected and the superconductor being affected would both be weird results on the surface. I had correctly guessed that the superconductor exhibited more resistance than expected, but the LN2 still had to be ruled out to be sure.
.. we call this an induction stove - and it can be bought in any store for electric supplies .. we have been using that for over 10 years in our kitchen .. (pretty neat, as it has a glas surface)
The induced curent is equal to voltage divided by resistance according to ohms law. Meaning lower resistance will heat more. The copper penny probably heats less because its mostly zinc and not really copper.
My soldering iron is induction. There is a small coil in the end of each tip and the core of the tip is different alloys depending on the temp of the tip you select.
Hi. I have been watching and subbed to your shorts forever. I just found this channel today. I want to tell you I've Keane so much about science just from watching your channel. You make it so fun & interesting. I didn't pay much attention in school and have been left questioning a lot of things happening in the world. You explain a whole lot. Thank you. ❤️
Please, do more experiments with super conductors
It should be added that ferromagnetic materials will also experience a heating effect from magnetisation hysteresis losses. They get magnetised by the field from the coils. Every time the magnetisation switches, some heat is generated.
This effect is usually much stronger than the heating from eddy currents. That's why only steel pots work on induction hobs.
Also why the bolt heats so quickly up to ~orange heat when standing up, but kind of just stalls out at that point!
I was also surprised. That's Wild!
Oh my god i was looking for these videos, make more superconductor videos. I like it.
This is really interesting and I'd like to understand it more. First, I think we need to understand how the temperature of the solid gets increased. I guess the main process is electrons inelastically scattering off the lattice and transferring their energy to the lattice. If we calcualte the temperature of the electrons (here "temperature" basically means kinetic energy), it will be huge. The temperature we are feeling is actually the temperature of the lattice. (I guess this is not contradictory because electrons have a much smaller heat capacity than the lattice.) Therefore, the heating effect we get by the electric current is actually of a different mechanism than zero resistivity, which concerns the interaction between electrons and disorder. The disorder scattering is typically assumed to be elastic so I guess it doesn't play a role in the heating.
Then, the heating will happen as long as we have a current so the situation should be similar to that of a normal metal. However, I believe the material you are using is an insulator, so actually the real interesting thing the superconductivity is doing is to induce a current (the Meissner effect induced a current to keep the magnetic field constant). I guess we always use some kind of metal to do induction heating but by virtue of superconductivity we can use an insulator to do it.
I love superconductors and would love to see more vidoes about them. Thanks.
Great experiment. Thank you for doing and sharing it.
Good one.
You should have shown the temperature variance of the supper conductor
Amazing experience, however, there is another reason for induction heating effect besides the skin depth, ur YBCO is not a single crystal disk and magnetic field induce heating through grains via boundary interaction and crystal defects.
Best Channel For Science Experiments ... Action Packed ...
This guy is doing actual magic I love this channel
I think I read somewhere that the reason superconductor locks magnet in place is due to the imperfection with induce eddy currents , although I am not sure if it matters , I want know if it has some significance
The imperfections in type 2 superconductors allow the magnetic field to penetrate it (this allows the quantum locking) but it doesn't change the fact that there is 0 resistance inside the conductor. But it does mean that the skin effect is also surrounding the imperfections. So a type 2 superconductor would have worse skin effect than a type 1 superconductor.
@@TheActionLab oh cool!
And that’s why I love my iSiler induction stove.
I am wondering that the frequency of the current applied into the induction coil depends on the power supply you use. That means, when you turn on and off the switch, there is a step change that changes the frequency profile of the applied current unless the power supply has a mechanism to regulate these spikes and harmonics. In my opinion, these high frequency noises and harmonics may have very low averaged amplitude; but may be enough to penetrate the very thin skin depth of the superconductor. This may not be a big deal unless the experiment requires to find the change in boiling temperature as a function of frequency.
I have the answer as I make superconducting pucks.
The superconductor layer is very thin (less than a human hair in thickness) so it is in a sandwich of stainless steel and copper.
In addition these ribbons are soldered together more than likely to add up to the diameter so this would introduce tin and maybe lead.
The ultimate experiment would be to use a single domain chunk of YBCO or some BSCCO superconductor.
I've actually done a similar experiment with putting a chunk of YCBO in the microwave. When warm it sparks but under liquid nitrogen it does nothing! I made a video but never posted because I wasn't happy with my camera set up so .... feel free to try it! (with a chunk of pure)
Interesting I've only seen these pucks as powered ReBCO compressed in a mold instead of proper crystalline tape stacks. It would change the electrodynamics of the situation quite a bit, coupling losses would be much more significant. Wouldn't expect it to work as well as a "quantum locking" demonstrator then though.
This was actually surprising
Huh, I’ve got it right. Thanks ty my two yrs as an assistant in cryo lab back at uni. Kudos to Kamerlingh Onnes for discovering superconductivity.
I kinda wanna see some "electrolyte solution" in the induction heater
Man you should look into magnetrons and thin film deposition!
Excellent experiment and video!
Beware with galvanised steel parts. Zinc fumes can be extremely toxic.
Loving the Cyberpunk Arc with that hairstyle lol
Love the samurai bun.
Great vid
It can partially also be because of the fact that nothing can be a perfect conductor even superconductors have some resistance which is very less than the resistance of normal conductors but still it is more than 0 resistance.
Normally I don't care for your content. This was actually pretty well done.
3:58 I think the supeconductor will heat up. The eddy currents will still happen after all, and will keep changing direction. This will dump some energy into the superconductor.
Excellent. We do love discovery!
I would like to see 2 more test if your up for it. 1. Put a magnet in a cup of water in the coil to see if it heats up. 2. Raise the induction coil to a height where you can have the superconductor levitate the magnet below the cup and coil while turning on the induction coil to see if it drops the magnet or does something different.
Test #3 carbon graphite welding rods in the cup of water.
Also in the test with the magnet in water see if it loses it's magnetism by having some paperclips on the bottom of the cup as you turn on the coil.
👍👍👍👍👍
I think this superconductor mostly consists of a superconductive phase which is continuous throughout the sample with small inclusions of non-superconductive phase and it is responsible for heating up the sample
You should do it again but have the magnet on it while you heat it up. I'm curious as to if that would have any effect on the magnet
I love he just casually toss in LN and it slashed
it usually wont burn you because of leidenfrost effect
@@GigsTaggart i forgot it could work the other way
I'm glad I didn't predict the outcome haha. Very interesting, thanks!
Incredible experiments! Best physics teacher in the world :)
I really was surprised by what occurred with the superconductor. I expected it to ignore the alternating magnetic fields until it warmed up some, then it would react more and more. But, even when you refroze the superconductor it still had a reaction when I assumed it wouldn't. I don't know if you were pretending to be surprised or really surprised, but I really was. I didn't know that superconductors has a penetration depth even when cooled or the other mechanisms you were starting to allude to in your pinned comment. Very interesting stuff!
Is it because you just heating the metal and the superconductor and the temperature of the liquid nitrogen increase, so it wants to evaporate faster. The opposite of cooling down and stop boiling. Is the answer that simple?
Yup.
WOW not what i expected
The laughs sound like a mad scientist, so good
As does the hair, ahahahaha🤣
Thanks ❤️
Wonderful experiment. I loved it
Are there imperfections or surface effects on the superconductor? Like, localized impurities at the surface?
Edit: aaaand sort of yes. It was a surface effect after all.
They are bulk effects. Depending on the size of the field, it happens throughout the entire superconductor.
Induction coils are pretty amazing --and efficient too. I have seen a Russian maker put a crucible inside the coils to melt & cast metal.
It's not all THAT efficient -- the coil is water cooled with good reason! Typical for a furnace might be 70%, which is still quite a lot better than gas-fired though.
@@T3sl4 ah, I had not realised that the coil was water-cooled.
What a fantastic video, thank you!
High frequency dissipation in superconductors is covered in the Michael Tinkham book (Introduction to Superconductivity) chapter 2.5.2 - there's a rather elegant and simple description there. In essence, even in the superconducting state, not all electrons are part of the superfluid (unless you are at absolute zero, which is unattainable anyways). Under a DC current, the "super" electrons will short circuit the coexisting normal electrons, giving zero resistance and zero DC heating. Yet under an AC current, the "super" electrons will no longer be able to fully screen out the electric field, and the rest normal electrons will be dragged around by the applied field - although at a reduced intensity - and dissipate energy in the form of heat. This is also the reason why there is still loss in superconducting cavities for microwave applications (such as quantum computing). As a visual demonstration, it'd be fun to dial the frequency of your inductive heater, and monitor how the boiling rate changes!
Another nuance here is the YBCO used, which means you have a type-II superconductor. The lower critical field of YBCO is actually quite low at only 0.01-0.05 Tesla level. This means you may as well get superconducting vortices (very tiny though) consisting of normal electrons in them. Under an AC current, this creates a lot of superconducting-normal electron boundaries, which can be another source of dissipation.
* There is also a finite amount of energy being leaked out/transmitted from the power source to the conductor...
They penny pictured is 97.5% zinc, so calling it copper is a stretch.
Love your new haircut