@uzless saidReading that article it seems the scientists don't know why they are confined to thin sheets of conductivity.
Any thoughts why the electrons from superconductors move in a 2d space rather than 3d?
https://www.scientificamerican.com/article/electrons-can-form-bizarre-2-d-flatland-in-superconductor/
It must have something to do with electrons seeking the lowest energy state like forces above and below channeling the electrons.
So the question I imagine they will have to answer among others, is what happens if the material is thinned out to one single layer of one crystal structure? Will the 2D nature still hold out and what about much thicker layers, same 2D thing?
Also how about changes of directions of flow, like say you have a straight wire with electrons flowing, when they go from a straight line to a curved line they slow down because inductive impedance goes up, slowing the movement of said electrons at least in normal room temperature conductors like copper or silver.
Does that same change in inductance happen if the superconductor is bent do the electrons also slow down going into a curve?
If a wire is wrapped in a circle, like around a cylinder, the inductive impedance goes way up and there are relatively simple formula to calculate the inductance from variables like the radius of the cylinder and number of turns and how thick the wire is and such, and any change in the flow rate slows down the movement of electrons, Total DC voltage without changing currents don't get slowed down but the faster the change in current like say an RF signal say one megahertz the current flow gets smaller and in fact the inductor is like a resistor but follows somewhat different rules, like the higher the frequency the more resistance to changing flow which is called inductive impedance, similar to resistors and uses the same name, Ohms, except in the case where there are turns of wire wrapped around a form of some kind, it would be called impedance but still using Ohms as the unit.
@sonhouse
I think it just goes to show that at quantum levels, 'things' no longer exist. So-called particles (electrons, photons, etc.) are not little billiard balls with sensible properties like shape or even definite location. They are quanta of measurable energy.
@moonbus
Sure but they still have traits like 'spin' which I have not yet figured out if it is real physical spinning of a particle or if it is more like a force field producing an effect like spin and not physically spinning. Just my half baked idea of course.
One question I have about photons is how can a massless particle impart momentum, that is to say, impart a kinetic force that now is used in experimental devices like solar sails which if implemented correctly can give thrust without fuel or shooting crap out the ass end as in rockets.
Solar sails don't do any of that, they produce propulsion with no fuel other than the light blasting out in all directions from the sun and they can steer a craft besides just getting propulsion much like wind sails on Earth.
@sonhouse
When I was a kid, I had a science toy; can't remember the name of it now, but it was a windmill-like thing inside a vacuum glass. The windmill-like thing consisted of four panels suspended on a pin, and the panels were painted white on one side and black on the other side. Left in direct sunlight, the thing would twirl around, apparently simply from the light being reflected from the white sides and absorbed by the black sides. I'm sure you had one, too. There you have momentum from massless particles. Clearly they exert something analogous to pressure by being either reflected or absorbed.
@moonbus saidYep, had one I think it is called a radiometer, invented by Crooks so it was also Crooks mill or something like that.
@sonhouse
When I was a kid, I had a science toy; can't remember the name of it now, but it was a windmill-like thing inside a vacuum glass. The windmill-like thing consisted of four panels suspended on a pin, and the panels were painted white on one side and black on the other side. Left in direct sunlight, the thing would twirl around, apparently simply from the light bei ...[text shortened]... particles. Clearly they exert something analogous to pressure by being either reflected or absorbed.
I think I tried light on the black side V the white side and I think it didn't make much difference which color was shown, like you said, photons exert momentum.
BTW that also works at lower frequencies but with less momentum generated, like it would not work too well as a solar sail if you banged it with microwaves, I imagine it would accelerate but at a much lower rate than optical frequencies which is low enough even with visible light.
One caveat about the Crooks radiometer, it depends on a small amount of gas inside the bulb to create a pressure differential and if there was a really good vacuum inside there would not be enough light pressure to move the vanes, they would stand still, I imagine at some big increase in light intensity they would move but the actual momentum imparted is way too low for the area of the vanes to overcome friction of the center bearing.
It has to be in space for light to actually move the vanes but it would take a lot bigger vanes to cause it to spin. I don't think anyone has done that exact experiment, mainly trying out solar sails on a smaller scale than real spacecraft would need to get useful acceleration.
I wonder if anyone has tried spinning the radiometer vanes in a good vacuum, say 1E-6 level which is a half ass decent vacuum I used to work with in my ion implanter days and sputtering tools.
My implanters and the sputtering tools could reach -8 scale vacuum, a hundred times better than 1 -6 level which is useful for implants and sputtering.
So I can imagine a great vacuum, even the relatively low level of 1 -6 showing a normal level intensity light not moving the vanes but then what luminosity level would actually be required to overcome the bearing friction and start spinning in spite of there not being enough gas in it to get pressure differentials allowing the vanes to rotate.
With that in mind, could a modified version be built with say magnetic suspension, would that lower effective friction enough to allow regular light intensity to spin the vanes? or would there still be enough friction from eddy currents of a moving vane structure to kill the spin?
@sonhouse
The magnetic field generator would cost more energy than you would get out of the spinning vanes, and a magnetic field might possibly interfere with the photon flow. I would try to go for reducing the friction of the bearing. The lowest friction I can think of is ice on ice, which is fairly easy to maintain in outer space.
@moonbus saidYou are thinking electromagnets. I was thinking of fixed field magnets but very lightweight ones, the bottom magnet could have some mass but the ones holding the vanes up would have to be very light and same poles facing down so it floats.
@sonhouse
The magnetic field generator would cost more energy than you would get out of the spinning vanes, and a magnetic field might possibly interfere with the photon flow. I would try to go for reducing the friction of the bearing. The lowest friction I can think of is ice on ice, which is fairly easy to maintain in outer space.
It would be tricky to keep centered and stable though.
@moonbus saidDo you know how to calculate the 'friction' for the best I can call it, the resistance to movement of two permanent magnets same poles facing so they can do the job of a bearing, I know that system is used in energy storage systems where the disks are inside a vacuum chamber so there is little air drag and the disk is held in place only by magnetic fields which would presumably have less rolling 'friction' for want of a better term, I guess you could say eddy currents effecting drag of two magnets one of which is turning on an axis, do you know of a formula to figure that out? With the idea of making a magnetically supported crooks manometer or any other kind of magnetically isolated spinning mass like energy storage, like how long the spinning part of a magnet would take to go from its max RPM to zero or some lower RPM number?
@sonhouse
Yes, I was assuming electromagnets. Could work with static ones, too.
@sonhouse
See
https://www.diva-portal.org/smash/get/diva2:730652/FULLTEXT01.pdf
... page 4, where magnetic bearings are mentioned as one application for repulsive permanent magnets (a formula is not mentioned at that point in the article, though it might be later on --haven't read through the whole article yet).
One stumbling block to using permanent magnets as a low-friction bearing is that repulsive poles brought into close proximity tend to demagnetize each other over time. Sorry, our dream of a perpetual motion machine using magnets in a radiometer seems bound to fail. 😢
@moonbus saidOh hell, MILLIONS of megawatts down the drain🙂
@sonhouse
See
https://www.diva-portal.org/smash/get/diva2:730652/FULLTEXT01.pdf
... page 4, where magnetic bearings are mentioned as one application for repulsive permanent magnets (a formula is not mentioned at that point in the article, though it might be later on --haven't read through the whole article yet).
One stumbling block to using permanent magnets as a ...[text shortened]... rry, our dream of a perpetual motion machine using magnets in a radiometer seems bound to fail. 😢
Well losing field strength wouldn't be much of a problem for the low field strength of the magnets needed for our little bearing. Those mags used for energy storing lasts a long time and we are holding up what, a gram of stuff? 2 grams?
My guess is if one was developed there would have to be one on top of the little post and another one on the bottom post, so the guts are totally isolated and hopefully stable enough to spin without freaking out🙂 Like wobbling which would probably be a positive feedback loop leading to it wasting energy when the input energy momentum wise would be miniscule.
I read the paper you reported, one question, it says Jm = Delta x M. Can't write the triangle showing so called it delta. Do you know what that figure represents?
That paper said they didn't experience demagnitization but did see a small amount that bounced back after pushing the magnets pole to pole touching but it was temporary and the fields popped back to original strength after some amount of time.
@sonhouse
Sorry, can't help you with delta formula -- beyond my competence. Oh well, back to the drawing board. I do like the idea of dual vanes, above and below -- after all, we're in zero-g, so no reason not to take advantage of weightlessness. Know a good patent lawyer ?
@moonbus saidWouldn't it be funny if we actually came up with an improved version of the Crooks toy?
@sonhouse
Sorry, can't help you with delta formula -- beyond my competence. Oh well, back to the drawing board. I do like the idea of dual vanes, above and below -- after all, we're in zero-g, so no reason not to take advantage of weightlessness. Know a good patent lawyer ?
My goal would be to lower the bearing friction so low it could work in a total vacuum, like my ion implanters, -6,-7 level or so showing the direct conversion of light to movement which as the crooks toy is right now, that is not the case, there is an intermediary in that there has to be a small amount of air, enough to make a pressure differential but not so much as full 15 PSI would create too much friction in just the air itself stopping motion but a newer version not needing any air at all so there would be that much less operational friction in air drag also.
Also was thinking of different shaped vanes, like maybe squirrel cage shape like those blower motors where each vane would be black or whatever facilitates the light reaction.
@sonhouse
I like the idea of a water-wheel shaped rotor, rather than four simple vanes, as this increases the efficiency. Still not sure how we get the motion out of the enclosure though. A rotor which doesn't attach to anything else isn't doing any useful work, it's just a widget.