How a Crookes radiometer works
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- Опубліковано 16 вер 2024
- A Crookes radiometer is driven by a thermal gas effect, and not "light pressure" as often thought. I demonstrate the radiometer in a vacuum chamber and explain its optimal running pressure.
en.wikipedia.or...
Mister, this is the best, simple explanation of this phenomenon I have ever seen, heard, or read.
Old video. Hope you're still out there.
You should definitely make one with 1.5 cm vanes and then one with .5cm vanes and see if there is a linear link to the gas molecules. That'd be very interesting!
3cm^2 vanes
These radiometers are neat. I vividly remember when I was a kid going to a planetarium and looking at one of these. Nice video!
Very interesting! This is the best example of describing what's going on I've found yet. Thank you for deep diving into it!
How can one resist such temptations?
You truly are a man of iron will
Fascinating as always! Thanks Ben!
i recognize this guy w2aew :) i guess you're a little bit famous then :)
So in the argument I had with my high-school science teacher 30 years ago, I was right. Huh. I wonder if I can find him to say 'told ya'.
I was taught that it was photons as well.
SimoWill, I think your high-school teacher will be more impressed that you still have that vibrant enquiring mind of yours.
The phenomenon where a radiometer rotates in the opposite direction when refrigerated or cooled is often attributed to the gas inside the radiometer. When the radiometer is heated, the gas inside the bulb expands, creating a pressure imbalance that causes the vanes to rotate. Conversely, when the radiometer is cooled, the gas inside contracts, generating a pressure difference that leads to the rotation in the opposite direction. This effect is primarily due to changes in gas pressure rather than changes in light intensity
I’ve just watched this and practically jumped up when you said you might try to make a radiometer with larger blades. I’ll be looking for that right now, but if you haven’t *please* do!
Loved this! Subscribed.
This is very thorough and informative. Thank you for taking the time to give this a proper explanation.
I was told in science class in 2003 that this was due to light hitting the sides not heat. I remember being confused at the time of the direction it spun.
Good to know. thanks for the video!
I haven't even watched the whole video and I have clicked the like button..........
This is amazing stuff.........and the experiment is making it more interesting.
Wait wait wait!!!! You never ever explained how it moves Backwards when cold!!!
And you really skipped over how the "second " way it turned works!!
Thank you for the video but we NEED MORE!!!
Thanks!
The scientific term for the force is "Photophoretic force". Your observation is very interesting because in micro particles the force peaks when the mean-free-path of the gas is the same as the diameter of the particles. This force can be used to trap and guid particles which absorbs light.
I'm very curious to see the results of the larger one. I hope you decide to make it! Great video!
I don't quite understand why the effect just happens at the edges.
Blown away with the freezer spray cooling even repeated that one at home to see it again. Did not expect that to work still thinking about it.
The first time I saw one of these I was told that the force was delivered by the photons.
Great video man.
Well done. Operation clearly explained. Very engaging by using a vacuum chamber and oscilloscope to collect data from sensor.
Always love your experiments.
I can remember hundreds of radiometers on a big table for sale, at Disneyland.
I think you should switch the colors so we can have more data. It cold be related to the vibration of the atoms that can absorb kinetic energy from one place and releases to another, just like a sound levitation but in a form of radiation. The energy travels through the gas molecule in certain frequency, if there's no gas,the eneryt can not be transferred, if there are to much gas, it cancels each other out. Try with magnetic sheets, cover with black and white and see if works in a vacuum.
The spin is caused by the temperature gradient you're creating. Very cool.
As the effect depends on a thermal gradient between the two sides of the vane, making the vane of ceramic or other insulating material should enhance the effect.
Yes, I wondered about that. If the vanes are thin sheet metal one would have thought black and white sides were almost the same temperature but the black side is radiating more heat and heating the nearby air molecules thereby setting up a heat gradient in the air and hence a pressure gradient.
So I had been fooled to believe all this time that it was radiation pressure. Now I understand why I couldn't understand it...because it couldn't be radiation pressure! Thanks for the clear clarification.
Been watcing a few videos on this, glad to see you made one as I trust you on such matters the most.
I think I'm picking up what you're laying down but
A: What info is given with the packaging? You just did a really cool experiment to find out info that I feel like the makers could easily include or even print onto the base. It's a learning tool for Pete's sake.
B: I am now angry at every science teacher I had that had one of these on the shelf (almost all of them) and never brought it up or just had it so we could look at the spinny thing and not bother them for awhile.
This is a great experiment Ben, thank you. I enjoy all your videos, explanations and analyses, but this one really got my mind *spinning*. Thumbs up
Great video. Way better explanation than the other suggested video. And a good demonstration!
Very good experiment, thank you! I read a theory that the gas or air curls/coils around the edges of the flags and pushes from opposite side, i imagine like the air flows around the back end of a semi truck when driving down the highway.
You should try adding a fractal edge to the vane (increasing the perimeter for thermal transpiration).
Thanks for your explanation. Very nice! What would happen if the center of each vane would be removed? It would seem it would spin faster as there would be more "edge" to affect.
I would love to see the difference between two radiometers at the same pressure, but one with say helium, and the other sulfur hexafluoride, or another dense gas, and see the difference between them at varying pressure levels.
it would be interesting if you use infra-red camera to observe, also i would use 4 light positioned in all directions to determine the heat cycle.
Very clever device. I liked the experimentation and investigation. Very cool physics demonstration, this radiometer
I think it was James Clerk [pronounced 'Clark'] Maxwell who, in a lunch break, elucidated the workings of these things.
When I go my first vacuum system I used a naked radiometer as a rough indicator of vacuum. I now use a Pirani and a Penning gauge. Was that Volts/vacuum table for an ion gauge? I have one that I must get around to fitting. The naked radiometer now sites on a shelf as a 'curlometer' for the air field in the room.
My old baseplate had expensive Edwards feed-throughs, and I needed more, for which I used RF feed-throughs soldered into a plug that replaced a single HT feed-through. I was thinking of sparkplugs. Do you use their standard seals? Do you plugs a good solution?
I am envious of the turbo-molecular pump; I still use diff pumps. I note that the TM pump's maw is off centre. My original baseplate had it in the centre, but that gave little space for experiments, so I made a baseplate with an offset hole.
Now that the Technology Connections channel pointed to this video I must keep an eye on the channel.
Hi Ben. This is interesting to me. I built a LED strobe light of about a dozen 100W LED panels for fun. I noticed some very strange things during each pulse. Holding something like a black piece of paper in front of the array of panels caused it to jump a bit in ambient air. I thought at first it was maybe the metal sheet I bolted the LED panels to since the high current travelling through the wires creates a magnetic field which interacted with any metal/magnets nearby, I thought maybe it was making the metal sheet vibrate because of this. Although this /was/ a contribution, I noticed the effects were greater on a black piece of paper in front of the array than on a white piece of paper (same paper, different colour). I know the variables are different, I used a ridiculous amount of current, and ridiculous light output. I presume this is the same kind of effect as demonstrated in this video? Enjoying your videos as always, keep it up!
Best explanation I've heard. Thumb up, Captain. Liked and subscribed.
If you decide to start making some experimental radiometers, how about making one with more edges? Holes punched through the vanes would add more edge area.
Yeah, I'm really curious to see one with waffle-pattern vanes, 1cm holes at 1cm spacing to begin with.
I had an idea the other day to make one with logo-shaped vanes, so this could be important for that I guess.
I would like to see one that has a fractal pattern.
helical
Very nice! Something I've always wanted to try.
Very cool and interesting video, really enjoyed your explanation.
Thanks for sharing! I love this channel. I am curious, was this whole experiment mainly for your viewers or were you curious yourself or did you have some other motivation to do all this?
Also, I would love to see more experiments that involve the vacuum chamber :-)
Thanks again!
Thanks! I really appreciate it. I am motivated quite a bit by basic curiosity, however having this youtube channel causes me to be more focused and productive. So, it's a win for everyone.
another thing can be observed, but can not be explained away by the random whole chamber air particles' thermal-dynamic bumping in black and shiny side of the vanes is: if you use a laser pointer, to shoot a beam of light ray onto the vanes, it will "push" the vanes to turn, the point of laser ray lands on the dark side of the vane relative to the turning axle works out as Newton's law of lever or torque and pivot when turning a disk or turning a waterwheel. It seems to indicate something different, I am guessing : Radiation The difference of thermal radiation forces exerted upon the black and shiny side of the vanes or radiometer. The reason the radiometer not only react to heat, light, but also react to coldness(mainly different amount of thermal radiation emitted from differently heated or chilled surfaces in case of ambient heat or cold propelling the vane). In the case of propelled by light, laser or sun light, the radiation force exerted onto the vane is not secondary thermal radiation emitted from hotter side of the glass shell of the radiometer,(heated or chilled by external thermal influences applied) , in this case, light itself is a initial and final source of the radiation which bounced its force or momentum onto the vanes, thus caused its turning ( and the spot that the light ray force applied has different torque in respective to its distance to the vane rotational axle ). Thus the radiation does have mass or momentum, if the radiation has particles in it(even energy particles) , these observations from radiometer may not enough to tell, but what if, ---- even radiation or energy waves has the capability of exerting force onto solid objects?! ( this is just a speculation )
Excellent experiment. Your physics teacher would be much pleased.
If it's an edge effect, I'd be interested to see what a grid or screen shape does!
Minute 5:40: this indeed is not a coincidence. Looking forward to next radiometer experiment!
Indeed.
Did you know that at the first part of the video, many people can't tell which way the fins are turning?? I am one of those..it even appears to reverse directions at this straight-on view! I had to watch it 'start' turning to be sure.
Since I was a kid, a radiometer is one thing that I wanted...decades later, I finally put one in a microwave oven (with a water load).. It turned very fast at first,then there was a spark at the tip of the needle (blunting it due to the high EF build-up)...never worked again...gotta get another one one of these days!
GREAT VIDEO!
I own a 5 year old radiometer. But about 2-3 years ago it stopped working. Sometimes it was sitting in bright sunlight without moving. Flicking the glass would make it go for a few minutes. This behavior increased over time. Nowadays I rarely see it moving.
Why ist that?
There is no information on that online but I came up with 2 possible answers. First one is the needle bearring. It is possible to be worn out over time. But after close inspection it seems to be fine and since it spins perfectly for a few minutes when touched I dont think thats a problem.
Another possible answer is that air diffuses through the glass into the radiometer. The increased drag could slow down the Blade bringing it to a stop.
However these are just best guesses.
I am genuinly curious whats happening.
So... did you ever make one with the larger vanes?
Somehow that's very unsettling, even if these values were most likely just a coincidence.
Would love to see a followup to this with the larger vanes.
@Electrical equipment TAO see 1) ua-cam.com/video/tKLV6xBNgks/v-deo.html & 2) ua-cam.com/video/-iCf6K91_No/v-deo.html
@@cryptonein I have to agree with Ken here too. Really fucking cool stuff!
@Electrical equipment TAO Thanks for that link; I think Ken is actually correct...
Can you fill the chamber with different gasses and see how that effects speed?
You are forgetting something very basic and very essential, the force on the white face is being split into momentum opposite the direction of that upon the black face, and reflected photons in the same direction as the pressure being exerted upon the black face. Therefore the pressure on the black face is greater than that of the white face, and the white face simple offers resistance, as well drag pulling it back with the reflected photons. Occam's Razor: The simplest explanation is usually the best. And if it was heat, light focused on the edge wouldn't cause it to move faster than light focused on the whole fin, because there is less heat being generated over a smaller space than if the whole thing were lit. But light concentrated at the edge and passing does create photon drag. Light is the result of energy and photons, which are matter and do have mass, Heat is the result of energy and friction. Neither one is actually part of the electromagnetic spectrum. You can light energy-level wavelengths with no photons agitated or excited, and not get light. You can have an energy that isn't even near the perceivable light wavelengths and have present photons become agitated enough to emit light. 60Hz AC is what a majority of the world's lights work on, meanwhile visible light is in the hundreds of terahertz. The energy level exciting the photons is far inferior to the energy of the light emitted. And light and heat aren't codependent either. And the shade of black is merely the resistance to photon reflection or passing. Black objects don't get hotter than white object if left in a dark room equidistant from the same source of heat, only when there is light involved, and light requires photons. The glass bulb it's encased in, like many lenses, excites photons with heat, transforming heat into light by exciting photons. Photon Pressure is not only the simplest explanation, it's the only one that isn't easily disproven by overlooked factors of the experiments that try to prove it. If you remove the lens by removing the bulb and putting it in a vacuum chamber at near vacuum, a light from inside the vacuum chamber can still cause it to spin, but a heating element won't. Because there is nothing to turn that heat energy into sufficient photon pressure. And the fact that when the bulb itself is heated creates infrared level photon agitation is NOT aside from the point, that is something ALMOSY EVERY video claiming to explain it actually claims at one point or another. If you remove that lens that allows heat to agitate photons, heat doesn't make it spin. And heating the base doesn't make it spin until the glass gets hot either. But let's ignore that because it disproves our supposed big brain theory that it's the heat and not the light. Glass and crystal emits a lot of light, both visible and not, as it heats up, the ceramic base doesn't. And a theory that disproves itself is not a sound theory and definitely not the right one. Heat is the closest theory to how it actually works, but there are so many ways that you can prove heat doesn't make it spin without heating up a piece of glass surrounding the fins. Also, it spins one way taking heat in, and the opposite when putting heat out. And when heat is output through glass, it created photon pressure on the side of the glass where the heat is escaping the glass. Reverse the direction the glass transfers heat and the spin reverses, sure. But we also know that glass transforms heat into photon pressure, emitting light. And the light is travelling the path of least resistance, out away. Light travels away from the van, the vane spins opposite the way it does with coming at it. Y'all should watch each other's videos for all the things that prove it isn't heat that are ignored. In any of them you can spot at least 1-3 reasons it isn't heat. Literally. Some of them as much as at least one proof per minute of video. Just because proof is overlooked doesn't mean it doesn't exist. This is why peer reviews are a thing. But even that fails when every peer reviewing the research has their own bias or interests that that proof could lay to waste, and it will often be refuted for that reason alone. It's like saying unicorns can't exist because that might mean god exists too, despite the fact that we just dug up a perfectly preserved unicorn from a glacier, horse body with fur intact, helical horn and all coming right from it's forehead, and I can't believe god might be real because I take the lack of current proof that god is real as proof that god isn't. And nobody likes to admit to being wrong, so they will discount your facts that are proven and known that contradicts their belief. When somebody BELIEVES something is wrong, it doesn't mean they know that it is wrong, but rather that they refuse to accept it as right. You can't know and believe the same thing, for the two are contradictory. Belief is something you take on faith and/or bias and not on fact, knowledge is something you take on proof and not bias and/or faith. And the search for scientific proof is often obscured by personal bias and belief. You can believe the world is flat and that the sun rises in the north and sets in the south all you want, but it is known that the earth is round and that the sun rises in the east and sets in the west because that's how the globe earth spins. If the earth was flat, you wouldn't see different stars and different seasons based on how far you are north or south of the equator, and we definitely wouldn't have night and day both present around half the world at the same time, it would either be all light or all dark, perhaps even all of the time based orientation of the planet. You can't portionaly light the surface of a disk regardless of angle of light source, either the whole surface is lit or none of it. But you can only ever light half of a sphere from a single angle. Stop looking at the experiments with the idea that your theory is right and has to be the only possible option, that is called an impractical bias, instead look at it as it's either right or it isn't and you intend to prove which. Because again, I see more proof that it isn't heat than that it isn't anything to do with light itself. Light is the reaction of energy and photons, heat is the result of energy and friction/resistance. We use thousand of devices every day that were made from KNOWING this, shy do we suddenly forget it when it comes to something like this? Light makes it spin with or with the glass in between the source and the vanes, heat only makes it spin with the glass in between the source and the vanes. Clearly it's not heat, or heat would make it spin even without the glass in between the fins and source. You can believe it is heat all you want, but the thing that has the most influence on regardless of variables is more likely to be the cause than the one that fails to have the same influence across as many variables, not the one that loses influence from the most variables. Again, Occam's Razor. The simple solution is often the best. Light continues to have influence on it with most of the variables that cause heat to lose influence, and thus far the only variable that prevents light from having an influence is full vacuum, and heat loses influence before light as it gets closer to full vacuum. Meanwhile, there are dozens of variables besides the glass bulb around it that effect heat's influence on. The sun pulls white objects and pushes black objects off course, and in the vacuum of space, we use solar sails successfully on that very concept, and even in a full vacuum it works where heat based thrust fails. And applying heat to solar sails has no impact unless done so through a lens that manipulates and excites photons, it is very much how we direct satellites and space telescopes, as well as probes sent off to the depths of space. More efficiently than either mass displacement or heat displacement thrust at that. In a vacuum on the earth's surface, there is still one factor that is not present in space, and that is mass gravitational pull, the greatest factor of resistance being ignored in all of these experiments. The more effect gravity has on the vane, the less impact any other external force can have on it.
My guess is that the light is absorbed by the black face and re-emitted as long wave IR. This transfers heat to the air molecules in front of the black face, causing a slight increase in pressure and making it move. It has to be low enough pressure so that there is less air resistance so all the vanes can move easier.
The plethora of spark plugs in the vacuum chamber has me very curious!
They are probably high voltage feedthruoghs.
Data is beautiful, as they say. Great stuff. Would be very interested in the larger vanes and other possible variable tweaking. Gas composition? energy wavelength? Do the black and white faces need to be bonded thermally?
My high school science teacher told me 'porky pies', photons indeed,
made him sound smart.
Thanks for clearing that up Ben.
catch ya. Triggy.
Any element that has a dominate Nuclear Right Hand Spin is dominantly North-Polarity and any element that has a dominantly Left-Hand Spin is a South Polarity. When freezing a Right -Hand Spin Element, it will change the directional Nuclear spin and become a South-Polarity, as will a left-Hand Spin Element, will go from a South-Polarity to a North-Polarity when very cold. This is why the Crookes Radiometer changes the direction of its Spin, when made to be cold. Robert Shrewsbury March 11/2022
if the thermal creep explanation was correct ....then red light would also have turned it cause it gives more infrared signature ...but it doesn't ... only purple and white light does
I love your explanation on radiometer, especially using oscilloscope. :D
Fascinating exposition Ben. Great. :)
Rockin that 2014 eeePC
This is great demonstration. However to clear things to those less familiar with Torr, militorr scale> 7 mTorr is equal to 0.00000933256579 bar. (Or 0.9 Pa to those SI compatible people out there.) This pressure is kind of close to zero. We are not talking about Mount Everest air pressure heights as the corresponding air pressure is at about 40 km above the surface. Or 25 miles. This is the height the Google Exec just jumped recently setting a new record in sky jumping heights.
Torr bar and Pa are well known among all the thing that confuse a SI person is the imperial nonsense
I actually had to lookup mTorr. I know SI pressure and I am familiar with bar and psi.
And really wanted to know what kind of vacuum we are talking about here.
Hello! I love your channel. Just wondering, did you ever get to do the changes in vane sizes? I'm rather curious about that. Thanks!
+Doxie Lain Thanks! No, I haven't returned to the radiometer project since making the video. I have a long list of things to do.
+Applied Science There's also the corollary to consider: is there a smaller length at which a radiometer would work at a pressure that's closer to what we're used to? Testable by going bigger, rather than smaller, of course.
+Applied Science Hi! Love your channel too! Would you be willing to share the Excel data that you collected? I'm thinking about trying to duplicate your experiment, maybe test the different sizes of vanes.
OMG! As a child I was lied to! Excellent!
I think sir it's both, it's being moved more by photons at the same time, slightly with heat, specifically with heat differential (much like how earth's wind works, when there's warm and cold air, cold air on the other side) because I tested it with bright LED light vs. 100 Celsius SMD heat gun (about a few centimeters), it spun faster with the bright LED light (almost touching the LED reading lamp) than with just heat.
A laser pointer may make it spin very fast without melting the bulb (it might explode). I wonder if a very high laser is shown, like blue laser but not intense enough to damage it?
Were the sources inside the glass vacuum vessel, or outside? The glass will intercept some IR ...
When he talks about how it's not the photons creating the effect, he says that if it was, the force photons reflecting off of the white surface would be greater than the ones being absorbed by the black surface causing it to rotate in the opposite direction.
My question is, why do the photons that are hitting the white surface have more of an impact than the ones hitting the white surface?
I would have thought, since the photons hitting both surfaces have the same energy, they would cancel each other out and there would be no rotation.
P.S. I don't know too much about light.
You are correct that the incoming photons have the same energy when hitting the white and black faces. The difference is that they have a much higher chance of being absorbed when hitting the black face, and a higher chance of being reflected when hitting the white face. If they are reflected, more momentum is transferred to the face because there is now an outgoing (reflected) photon that has "pushed off" of the face. In the absorption case, there is no outgoing electron, so no additional momentum. A perfectly reflective mirror surface would produce the most force from an incoming beam of light. The diffuse white surface will be less efficient because photons will be reflected in all different directions. Search for "Pelton wheel" to see a nice physical analogy.
Thanks. I'll look into that.
Newtonian physics as we know it, bouncing something with mass transfers more momentum to both bodies.
(that's why punching something and braking it is safer than punching really hard and not break it)
but 'photons' are massless we cannot apply the same thinking here.
light are not particles(massless) it is a wave. imagine a water wave when does it transfer momentum ??
you could simply cut away at the vanes to make them smaller. This would also eliminate the variability of different coating thicknesses, etc on each manufactured set of larger vanes. and it's a lot easier.
What effect do different light sources have on the speed of rotation? Do different wavelengths have different effects? It would be interesting if it responded well to a non visible part of the spectrum like infra red. You could make it rotate with no visible means of adding energy.
It would be great to see you make vanes of all different shapes, and sizes, and compare the performance. If you could make them light enough, you could even 3D-print some designs and test them, too.
very interesting experiment, thx for sharing with us
I would have liked to have seen how fast the radiometer spun at the optimal pressure! Though I'm guessing that's very close to the pressure that the sealed unit from the gift shop is made at.
If you do think of revisiting this. I'd love to see if different gas effect RPM. Also, different wavelengths of light. Would UV create more heat than IR? And of Course Vane size!
What I find interesting is how he happened across this. he was trying to make a perfect vacuum to get any air influence out of the picture. Because he accidentally did not make a perfect vacuum but only a partial one is why it even spun at all in the first place.
Does this work with round veins or do they need to be squares?
Also normal air pressure is 760 torr or 1 atm. The pressure in the tube is less than 1 torr. So its pretty close to a vacuum. I wonder if it could be done using a excitable gas one can be visualized? That way you could maybe see the currents in action.
I first saw this thing on an episode of Mister Wizard. Great show. =)
Sweet, very cool way to test this. I wonder if having vanes with a large edge:surface ratio would spin faster?
My Radiometer slowly lost its tenancy to spin after I left it in a sunny window for an afternoon. I'm not sure if something gassed off or if the needle/glass bearing experienced wear. It still goes but only with very strong light sources.
Possibly by sitting in full sun for a while the temperature of the whole system has warmed and the temperature difference between the two sides of the vans is less resulting in less of an affect. I don't know, maybe? Cheers, Mark
I thought that initially but it has stayed the same since then. Without a 500w light it refuses to get going :/
I think your pivot point has warn down. Think about it, to make the vanes able to spin with very little force exerted, the whole thing is suspended on a needle fine point; and as the vanes rotate, the two surfaces will wear each other down. So after a very long period of use, the turning motion of the vane assembly would wear down the needle fine point to become more blunt. The more blunt the needle, the more force must be exerted to induce motion. Hence the requirement for a brighter light. More light = more force.
The glass may have a very small hole which is causing air to leak in. It happens sometimes with electronic vacuum tubes.
Also, you can test the worn bearing hypothesis by getting another radiometer and testing how much the vanes rotate when the radiometer is rotated. If the bearing is worn, the vanes should move more than an unworn bearing.
@@chronos1002 I think like UV rays from the Sun affect many materials, it might have made the metal react and kinda corrode in some way making its surface rougher. Or maybe the vacuum might have reduced which then again lowers the RPM.
Did you get a chance to test your observation about 1 centimeter travel with larger veins? Thanks
Fascinating. I always wondered how these worked.
Best video describing this
In the first part of the video you applied cooling to the surface of the radiometer, which had an effect. Then, when you transferred the spinner to the vacuum chamber, you effectively had a chamber with more volume. Is the volume of the chamber relevant at all? I suspect this is not easy to test, although, perhaps you could introduce different sized containers into the vacuum chamber.
What about repeating the experiment at various ambient temperatures? Apparently, the outer surface of the chamber serves as a heat sink. If you could repeat the experiment at very high or very low ambient temperatures, would you see a difference in rotation speed? Which would be faster, and why?
Clever! Good information
As always, very interesting. Thanks for sharing.
I've always wondered why most of them have 4 vanes- if it was something they tested and was the best or just was the easiest to build and balance.
You also might have a chance to set a strange record- the largest lightmills I've ever seen had only slightly larger vanes set on longer arms. If you can scale one up to as big as will fit in your bell jar, you will probably be the largest by 10 times or more.
Very interesting. I've owned one of these for many years, ever since my Physics teacher demonstrated one. However, aren't the vanes slightly tilted? Like a fan? I always thought the effect was the black areas heating more quickly, then heating air molecules which then rose, further colliding with the tilted vane and causing it to spin. Similar to the little devices people place over candles to ring bells.
Please demonstrate a Hettner Radiometer, which has horizontal vanes with black and white zones.
interesting effect & explanation/demonstration. enjoyed it.
This is cool!
I am trying to recreate the experiment for my school project.
@Applied Science, What is the name of the equipment at the bottom? Did you buy or assemble it?
How did you have the turbo machinery pump connected to the bell jar with electronic controlled valve?
Also, how did you seal the tachometer wires inside the bell jar and connected it to the oscilloscope?
I am trying to rebuild it but these things are a puzzle in my mind.
It would great if someone could answer it.
What a Pedagogical Quality Video! Thanks for your Obvious Application to make them, and if we make a Donation to Support You, I will :) 🙏
I would love to see the differences between larger and smaller radiometers and their optimal pressure.
Why would interaction only occur at the edges?
larger? Why not cut all the vanes down to half their size, and see if that changes things? Or cut a bunch of slits so there's loads more edges?
Larger vanes would be optimal for lower pressures? Does that imply that smaller vanes are optimal for higher pressures? How small would the vanes have to be to work at ambient press? 100nm? That's a small radiometer-100x smaller than a red blood cell.
Was there ever a continuation to this video ? I can't seem to find it. I'm really curious about the details how the effect can be amplified and what are the parameters that influence the rotation effect.
What is the material of the vanes? In the older one that I have (made in 90s), I'm guessing that they're painted aluminum. I'm trying to find what materials are typically used to make them and what else can be used.
Excellent vid! Thanks for sharing!
I wonder if there's a resonance happening? As well.
Can you write to us the full name of the:
1. Tool of measuring the pressure
2. Vacom ( the air pump)
??
good explanation
If there was a hole in the center of each vane, would the vanes spin faster since the total length of edges would be increased?
Nice. Can you get it spinning then turn off the light and film it with a night vision camera to see exactly where temperatures vary? Thx.
Is it running faster with CO2 atoms or slower?
Actually it should be slower right?
Simply, it just moves because the black side is heating up the molecules and they in turn move faster away from the black side thus creating the force?
Therefore with CO2 the gas will absorb more heat and there will be less heat coming from the black side?
Or will it be the same?
This is confusing!
Never saw this thing before, great video!
I think you could do a video about the chemicals in a e cigarette :) That would be extra cool.
I wonder how the smaller vanes would do if you cut a design into them to give them more edge space.
OMG, you are my new hero.... awesome video
Infrasound! Intelligent light!