Absolutely agree with you. I have watched many videos about this topic, no one can explain how the positive charges accumulate on the outer surface of the belt, but he did.
Finally, a person who explains this in detail! I don't get why other youtubers explain the Van de Graaff generator as a machine that simply collects electrons and they leave at that explanation, which is vague and does not really makes sense.
I have to agree with everyone - your explanation of how the charges move and where they're coming form and going to is perfect. This video needs to be made into a section in a physics or an electrical engineering text book, seriously. Thank you for laying it out. Your video is in my play list. I'm going to make a Van De Graaff generator too.
Just discovered you channel. I'm a fourth semester electric engineering student from Venezuela and this is just breathtaking for me. Thank you for the videos!
That's a perfectly reasonable question. A big use for them in the past was for generating high voltages, in the millions of volts, for particle accelerators for doing science experiments. I don't know if any particle accelerators still use them. These days they're mostly used in classrooms for teaching about electrostatics or by hobbyists who just like to play around with high voltages. Science museums also use them for demonstrating electrostatic phenomenon.
To understand Van de Graff Generator, I watched a lot of videos and this one was the most informative and useful one for me. Thank you for your effort! :)👏
Yes, by sharper surface I mean smaller in diameter. Assuming 79kv between two domes, the smallest diameter dome has the stronger electric field around it. The air molecules will be repelled from the smaller diameter one, and be attracted to the larger diameter one. And you're welcome. Glad I can help.
Yes, the effect only charges the inner side of the belt. But the main reason is that the charge on the inner side of the belt is spread out over the larger inner area of the belt. The roller, however, has a smaller surface area and so the charge is more compact, the voltage is higher. So we use that higher voltage to pull more charge onto the outer surface of the belt. As a result, the outer surface of the belt has more charge than the inner surface. It's that larger charge that we're after.
Thanks. It's a lot of fun (but also a huge amount of work) making these detailed ones. Two others which I'm proud of are How a Crystal Radio Works ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-0-PParSmwtE.html and How a Wimshurst Machine Works ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-nA4aCd5qFWs.html
Thanks. That's a big complement indeed. I spent 13 years traveling around the world teaching for a software company, I currently teach a few times a year for an adult education program, and have done other teaching and course development over the years. I can't seem to stop myself. :)
The motor has a power chord which is plugged into the wall socket to power the motor. That power chord has three wires: a black wire, a white wire, and a green wire called GROUND. That green ground wire goes through the wall socket and eventually to a metal rod in the ground in the backyard. That green ground wire is the one you see in the video at 2:04. The brush and the green ground wire are both connected to the metal case so they are connected together. Let me know if that doesn't help.
Thanks. The section explaining how the Faraday cage works is a little contentious since I wasn't using the standard approach to explaining it with just fields. But I really wanted to do it at the electron and proton level; more tangible, and also consistent with the rest of it. Have fun making your Van de Graaff generator. Be sure and check out my videos on that topic and ask questions if you run into problems.
Sorry, I don't know of a good website off-hand. I used my old high school physics textbook to double-check my knowledge of this. My approach was to first make sure my understanding of the relationship between electric fields and voltages was right. They're proportional to each other, denser e-field = higher voltage. Then I reminded myself that a charged VDG dome is a capacitor, with the room being the other plate. Since voltages are the same, e-field is the same, affect on ions is the same.
Das ist eine gute "How to"-Anleitung. Interessant war die Verwendung von Isolierband für den Antriebsriemen und wie man es auf die Rollen legt. Danke für die Zeit und Mühe, diese Videos zu machen. Es hilft vielen Menschen und inspiriert sie, etwas aufzubauen.
Yes, you can use the same materials with a small homemade van de graaff. In fact the small one I show at 2:12 in this video has a Teflon roller at the bottom and a metal roller at the top and uses a rubber band for the belt. Using metal for the top roller is less effective than using something that's triboelectrically positive with respect to the belt material but the teflon and rubber band combination works so well that the results are still very good.
(... continued) The same for a capacitor. The more charge you put on the cap plates, the stronger the electric field between the plates, the higher the voltage. The VDG dome and ground can be considered a capacitor. Pressure is sometimes useful analogy for voltage. By pumping more charge onto the dome you've built up the pressure. Bring a grounded ball close to the dome and the charge on the dome rearranges closer to the ball. The pressure may increase until the charge bursts across the gap.
Not usually. The electric field and resulting current flow are usually too weak. However, you can sometimes replace the regular multimeter probes with a high voltage probe to measure weak electric fields - by contact with the affected surfaces. You can see one of these probes in action in yet another of my videos :) "High Voltage Probe How-to with Fluke 80K-40".
Voltage is measured between 2 things. Example, my big VDG is rated at 500kV with respect to Earth ground since the lower brush is wired to Earth ground. To measure the voltage, use a HV probe. Connect the HV end of the probe to the dome and the other end to ground. The probe will feel the effect of the electric field between the dome and ground. The electric field strength is determined by the amount of charge. Picture one field line between each dome charge and a ground charge. (continued...)
Both of my VDGs in this video were bought, I didn't make them from scratch. The big one was from amazing1 dot com. They don't sell the domes separately. A lot of people make the domes by attaching two steel salad bowls together at their open ends and cutting a hole in the bottom of one. After you make the cut, smooth out the edge; sharp edges reduce the voltage. Note that VDGs produce high voltage but not a lot of energy; the current is very small.
Yes. Air contains a number of different atoms. One I know for sure gets ionized negatively is oxygen, which can then attach to an O2 molecule to produce ozone (O3). I'm don't know offhand which ones get positively charged. I talked about atoms becoming ionized in the video but molecules (which are made up of multiple atoms) can also become charged.
Actually, the photoelectric effect may happen with the positive brush (the bottom one) but I'm not sure that it does. With the negative brush (the top one) the electrons near the brush spread outward more and so the photoelectric effect plays a bigger part in contributing electrons to the corona.
even though I do not know English, the video is so didactic that I understood, thank you very much!!! from Brazil, translated by google translate hehehe
The charge would accumulate on their surfaces with most of it on the areas that face each other. As more and more charge accumulates, the electric field between them would become stronger and the air would start to ionize until finally it becomes conductive and an arc would occur between them. At that point the domes would no longer be charged and the whole process would start over again.
Off-hand I don't know. The faster it turns, the more charge you'll pump, so as high a gear ratio as you can do is the most I can suggest. It does depend on a number of things, probably the main one being how wide the contact area is where your belt contacts your roller, since that's where the charges are separated. The wider that is the slower you can turn and get a decent amount of charge.
You're right hat rubber is an insulator but that just means it's a poor conductor of electricity. It doesn't mean you can't deposit or take electrons away from it and that's what's going on when the rubber makes and breaks contact with the rollers. Then, instead of the charge conducting along the belt from one roller to the other roller, we move the belt. By physically moving the belt from one roller to the other we physically move the static charge too.
The charge is deposited using the triboelectric effect. When two particular materials make contact and then break contact, their molecules interact such that charge is exchanged while they are touching but doesn't get restore when the separate. The belt and rollers are constantly making and breaking contact. And yes, we are transporting the protons and electrons exactly like transporting materials on a simple conveyor belt. See my video Triboelectric video, see link in this video's description.
Thanks. I'm glad it helped. Yeah. as long as the connection is to the inside of the dome then you're okay. Connecting to the outside makes it much less efficient.
You can use a cylinder as long as one end is closed. So one end is open for the top part of the Van de Graaff and the opposite end is closed. Make sure to avoid having sharp edges though, as they'll decrease the output.
The upper brush is connected to the inside of the dome. Is that what you thought, or did the video somehow lead you to think it was connected to the inside? If so, which part of the video made you think that?
Charge leaks more easily to the surrounding air from sharp edges. Charges bunch up more at sharp edges creating a strong electric field which interacts strongly with the surrounding air. See 5:18 in the video. Now a large dome, by definition has a very smooth surface, no sharp edges. The larger it is the less round it is at any point. So you get less charge bunching up and weaker electric field. The charge stays on the dome instead of leaking to the air. That means a higher voltage. continued...
...continued. If you compare the two domes at 14:58 in the video you'll see the one on the left has a "sharper" surface than the one on the right. The one on the left can reach only 80kV because at that point the electric field around the dome is so strong that any more charge just leaks to the air. The one on the right is supposed to be able to reach 500kV before any additional charge leaks to the air. Let me know if that didn't clear it up.
The short explanation is that charge is sprayed onto the moving belt due to the action of the lower points. This charge is then carried up into the hollow metal dome. Faraday's ice pail experiment shows there can be no charge inside a hollow conductor so the charges migrate to the outside of the dome. The potential builds up until the air breaks down in a spark discharge . The energy for all this comes from the work done against the repulsive forces as the belt moves upwards.
It should work if you connect the brush to the INSIDE of the leydon jar, not the outer cylinder. It has to use the faraday ice pail effect. Avoid sharp edges on inside cylinder of the leyden jar if you can.
Funny. You asked the same question in the comment to my How to Make a Van de Graaff Generator video. I replied there (the answer was yes, and I suggested you watch this video which I guess you didn't since the answer's in it :)).
I don't have a video on that. Though if you look at my "How to make an electroscope" video it's the same thing that makes the leafs inside the jar spread apart. If the VDG dome is positively charged then the hair is also positively charged and since like charges repel each other, the hairs all repel, getting as far apart as they can. Similarly if the VDG is negative then the hair is negative and repels.
Oh, interesting idea, twisting the belt! I'm not sure if the Van de Graaff dome would still charge up but it might accumulate more on the rollers. Hmmm. Regarding no external power source, it wouldn't. You need an external power source and you can't accumulate energy more than you use.
Definitely not a stupid question. I wonder this myself. The only answer I can come up with is that most easy to do ways of making physical contact with the belt will wear down the belt over time. I've done this by having my ground wire touching a rubber belt. The wire scraped away the belt surface; there was rubber powder all over.
If you connected the battery to the outside of the sphere you wouldn't get any additional result. The sphere would just be at the voltage of whichever battery terminal you connected it to. Even if you connect it to the inside, the battery would need a circuit to conduct.
I'd love to do a video explaining how a tesla coils works. I looked around and saw the same thing you did. However, I don't have the same level of background with tesla coils as I do with Van de Graaff generators. For a tesla coil that would mean building a few different tesla coils, which I'd like to do but haven't had time yet. It's on my todo list but it'll take a while.
If you have an ice pail with a large enough opening, you could put the terminal of an electroscope inside and the electroscope leafs wouldn't repel each other. If you're not familiar with electroscopes, see my video "How to make an electroscope (DIY)" (to help you find is it's one of my oldest videos.)
If they're both at the same voltage then the effect on ions in the air would be the same. To have a voltage they must have a voltage with respect to something. Let's say the domes are at 79kV w.r.t. the room. Having the same voltage means the electric field lines are equally dense around both. Since one dome has a larger surface area, it must have more charge for there to be the same number of e-field lines as the smaller dome. With the same e-field density, the effect on ions is the same.
Thanks! During the last days I have been trying to make my own generator without success. Your video helps me a lot to see why my attempt didn't work. Now I *finally* understand why there is some charge accumulation at all (ie, which is the origin of the first charge gradient).
The machine and my animation are going in the same direction. It's just an illusion created by the fact that the belt and roller aren't featureless and the camera's frame rate is 29.97 frames per second (i.e. not continuous.) Looking at it I can see it going either way but mostly in the same direction as the animation. I don't see why it would matter where the comb is as long as it's facing some part where the belt and roller are in contact but not where they make or break contact.
No. The smaller dome will start leaking charge sooner than the bigger dome. My small commercially made Van de Graaff generator with the 3" dome is rated 80kV. My big commercially made one with the 14" dome is rated 500kV. So if I took the 14" dome and put it on my small VDG, it would accumulate more charge. I'd have to increase the length of the belt though since with a higher voltage, the dome's electric field would start interacting more with the other end in form of corona and then arcing.
I don't understand it fully enough at that level to say for sure but I think it's atomic. When the materials come together, chemical bonds form between atoms in some areas. When the materials are pulled apart, some atoms have a tendency to keep shared electrons and some have a tendency to give them away.
There are different ways to explain things, and at different level. My explanation was as a very low level. Maybe they're really both right. What was different in his explanation?
I've never looked for teflon material so I don't know how costly it is. I usually just use a plastic of some kind. It won't be dangerous. The voltage is high but the current is very small.
@lx0199 I purchased the generator years ago as a whole from Information Unlimited (I'll put the link to their website in the video description.) The unit itself is made by Science First (again, link in the description or just search for their name) and was a slightly different positive charge version of their # 615-3145. I don't see any spare rollers for sale on either of their websites, though Science First does sell the belts. Contact them to find out what the belt is made of.
Nice video with many details. There are some confusing parts though about the rollers! It's not clear, for example, why metal would give away extra electrons beyond neutralizing the inner belt? (there is no field after neutralization that would drag electrons and charge the belt) The current explanation concerning internal surface of the belt doesn't stand long term operation by breaking charge concervation law. For example, the given explanation tells that the belt brings negative or no charge to the bottom roller and always removes positive charge from it. This would inevitably cause unlimited growth of negative charge on the bottom roller. A similar thought experiment can be done for the upper roller too.
I've never measured the amount of energy. I guess that could be done by charging a capacitor and measuring the voltage after a chosen time. Then use energy = 1/2 * capacitance * voltage * voltage. But I suspect it's very small, far too small to operate a refrigerator. Plus, why would you? You may as well unplug the Van de Graaff from the wall power socket and plug the fridge in instead?
this is brilliant! I learned a lot from this video. can I make a request? can you make a video explaining how a tesla coil works? the other videos about the tesla coil doesnt a good explanation or is plain boring.
Why won't it kill? I think you're talking about the experiment where you stand on an insulated platform and put your hands on it before you turn it on. In that case the charge builds up on the VDG and on you gradually but it also leaks away from you when you turn it off. The danger is if you touch a big VDG AFTER it was turned on. In that case all the built up charge will leap at you at once. Depending on the size of the VDG, that may kill you. I won't go near my big one after it's already on.
Minute attention to every small steps of the generator and detailed description of its working... Really makes worth watching the...Really made the things so much easy and interesting...
