exchemist

Is a superconductor different, and if so why would that be?

I've come across an explanation , which I don't fully understand, for why a superconductor in a magnetic field experiences a force (the Meissner effect). It is said that eddy currents will be triggered in the superconductor which will form a perfect mirror image of the magnet, with like poles adjacent, so a repulsive force is generated. What I don't follow about this is I thought eddy currents were generated by a change in magnetic flux density, not by a static field. Does anyone know more?

To be honest I think to make progress in understanding this topic we should forget ChatGPT and have one of our physicists talk us through the Meissner-Ochsenfeld effect a bit. ChatGPT is basically as thick as mince and just plagiarises stuff it looks up on the web that it hopes is relevant, based on some algorithm. There's no reason to expect it to be able to do this stuff properly. But does it give you references for where it gets its formulae from? If we can read those sources we might get somewhere. Meanwhile, I've had another look at the Wiki article, which gives a remarkably simple formula for something called the "magnetic pressure" that a magnetic field exerts on a superconductor. This is Pmag = B²/μ₀, where P is force per unit area at the superconductor/field interface, in Pascals, B in Tesla. Here's the link: https://en.wikipedia.org/wiki/Magnetic_levitation What happens if you plug in the numbers for the Earth's field?

Doesn't the last of these just make you go orange - and become rash?

I don't see Russell on the list. That seems a curious omission. @TheVat's list is more the sort of thing I would have expected - though it is Eurocentric, I suppose.

OK, as this is homework, we ought to go through this in stages to help you understand, rather than just giving you the answer. First, do you understand why the aluminium ring jumps? Second, in the version with two rings, typically the second ring differs from the first in one important respect. What is this and why do you think it might make a difference to its behaviour?

Will it experience a force?

That's what I would have thought. But it would be nice if someone would care to summarise the Meissner-Ochsenfeld effect and what force it can generate. All I know is that a superconductor repels a magnetic field from its interior, but why this produces a force, in what direction, and of what magnitude for a given field strength, is something I have never studied. I had a quick look on Wiki but it was not very informative.

I know, but I read the query as assuming such waves could ignite it, so to disabuse the poster of that notion I tried to explain how gunpowder was actually ignited in practice.

No it was the felt hammer, inside the piano, that was painted. There was a bang, a certain amount of dust and dead ladybirds - and an eerie pause in the singing.

One snag I can think of is that the angle of the Earth's field is steeply inclined. So instead of just floating up or staying where you were, I would have though you would shoot off or slide down at an angle. But I'm not familiar with Meissner-Ochsenfeld effect so I'll have to let someone else check the robot's maths.

Yes, a few problems with your question. Firstly, radio and sound waves don't exert a force - or not to any significant extent - and secondly a force will not ignite gunpowder in any case. You need essentially to set fire to it somehow. You may have seen sailors firing c.18th cannons in films, for instance. That's why we call it "firing" them. A special match was used, applied to a hole in the gun and that would set it off. There was later something called the "percussion cap", in which a small amount of mercury fulminate, Hg(CNO)₂, was used. That is a highly unstable compound that will explode if struck sharply. This could be used to ignite the gunpowder. So with that system, applying a force, by hitting a capsule of this, could indirectly ignite a charge of gunpowder. There are other explosives that detonate when receiving a shock, most notoriously nitroglycerine, but also less hideously dangerous things such as picric acid* and nitrogen triiodide, both of which I have made at school, hem hem. But back to your question, there isn't actually the problem you imagine with gunpowder, so there is no need for your proposed solution. By the way, if you want to stop gunpowder from burning you just wet it. (In fact historically this was the basis of an early HM Customs and Excise test for distilled alcohol. "Proof spirit" was the weakest solution of alcohol in water which, when used to wet gunpowder, would not prevent it from burning.) * A friend of mine at university had a funny story about a school practical joke, involving painting the hammer of a single piano key with it, the key in question being played only in the bridging passage between two verses of the school song. You can probably imagine the effect.

If you mix up sugar yourself, though, you will need to measure or calculate the density for yourself. If you are prepared to do that, you could simply buy Lyle's Golden Syrup in the supermarket and use that.

I presume it has to be miscible with water. If so, would glycerol fit the bill?

Is Translate that bad?

Hovercraft eels ouant tobacconist bouncy bouncy.

What are you talking about?

“Fictional habitats”

Well yes. When you say "colonise", it implies taking over territory that was not previously theirs.

No. The water is adsorbed in the pores and will stay there. But the obvious thing to do is dry them out, in an oven at 120C for a few hours.

For colonisers they don't seem to be doing a very good job. Unless David Icke is right about the Lizard People, I suppose.

Yes, that could be it. Though I don't buy the notion it is unsafe to eat from dishes with cracked glaze. Bacteria and fungus are all around us and I don't see why a few traces in the cracks in a glazed dish are likely to be pathogenic.

You can put glass jars into a microwave and they stay cool. Though some glazes on earthenware get hot and crack (I have found, to my chagrin).

I suppose in theory, as it is water that is absorbing the microwaves, once it has gone the silica gel should cool down, as it should be transparent to microwaves of the frequency used. So the process ought to be OK, I think.

I'm quoting Douglas Adams but the point is a serious one. The distances involved are vast and massive bodies such as spacecraft can only travel at a fraction of c*. Physical travel from one habitable planet to another would take centuries, and centuries more to get back, and to what end? My own view is that intelligent life from elsewhere would have long ago realised it would be a colossal waste of time and instead would put their efforts into remote sensing - if they were interested in our planet at all. (It fact, it may be just arrogance on our part to imagine we would be that interesting.) * If it is proposed that alien civilisations may have found out how to travel faster than light, my response is that is unjustified, whimsical, wish-driven speculation rather than science. There is no objective reason so far to distrust Relativity.