Van de Graaff generator: device, principle of operation and application. Electrostatic toys and Van de Graaff generator. Science Toys Van de Graaf High Voltage Generator
In the early 1930s, Dr. Robert Van de Graaff, then a research assistant at the Massachusetts Institute of Technology and scientific research in the field of nuclear physics and accelerator technology, developed, designed and soon built a high-voltage electrostatic accelerator operating on the principle of a conveyor belt electrified by air ions (1933).
Later, in 1936, Van de Graaff built (all according to the same principle) the world's largest electrostatic DC generator - the Van de Graaff tandem generator, consisting of two tall towers.
Newspapers of that time called the invention of the assistant professor nothing less than revolutionary, predicted him to "perform miracles" and "discover the secrets of nature." Such a strong hype in the press is not at all surprising, because the largest two-stage Van de Graaff generator consisted of two huge columns with a diameter of almost 2 meters each and a height of about 15 meters (with metal spheres fixed on top of the columns with a diameter of 4.5 meters, inside which were mechanically supplied with an electric charge) and made it possible to obtain a potential difference of 7,000,000 volts.
Despite the low efficiency of the device as a whole (about 23%), people who saw the wonderful device in operation experienced an indelible impression, because spark discharges were more than a meter long.
The power of the Van de Graaff generator was enough for a real research work, - to speed up atomic nuclei, as well as elementary particles such as protons and electrons, up to enough high speeds. So the Van de Graaff generator, used in accelerators, helped scientists to identify the constituent parts of atoms, which are the structure of the physical universe.
They say that the idea of the principle of operation of a high-voltage generator came to Van de Graaff when he was still a student and observed the sparks of static electricity that were constantly jumping on a working printing press.
The principle of operation of the generator is as follows. Silk or rubber tape (dielectric tape) is stretched and rotates like a conveyor belt on a pair of rollers, one of which is located at the base of the column, the second is inside the cavity of the conductive sphere at the top. The lower roller is made of metal and is galvanically connected to the ground, it is driven by a motor. The top roller is dielectric.
A metal brush is connected to the tape from below, under the lower roller, with a small gap, connected to the positive terminal of the high voltage source, the negative terminal of which is connected directly to the lower roller.
So, a dielectric tape moves between the lower roller and the brush (in a real generator, the tape had a width of about 120 cm). Under the action of a high voltage (about 20,000 volts) between the roller and the brush, the air between them is ionized and the positive air ions, drawn by the Coulomb force, rush to the negatively charged roller. But since there is a dielectric tape in the way of the ions, the ions settle on the tape, charging it in this way.
The tape moves from bottom to top, at the bottom it continuously receives a charge, at the same time, the charge from its surface is continuously taken near the upper roller, since the upper roller inside the sphere also has a brush located next to it. The brush removes the charge from the tape, and being galvanically connected to inner surface conductive sphere, transfers a charge to it, more and more electrifying this spherical capacitance throughout its outer surface, essentially pumping, pumping a charge into it.
Otherwise, it may be questioned and removed.
.php?title=%D0%93%D0%B5%D0%BD%D0%B5%D1%80%D0%B0%D1%82%D0%BE%D1%80_%D0%92%D0%B0% D0%BD_%D0%B4%D0%B5_%D0%93%D1%80%D0%B0%D0%B0%D1%84%D0%B0&action=edit edit] this article by adding links to .
This mark is set February 17, 2013.
Van de Graaff generator- high voltage generator, the principle of operation of which is based on the electrification of a moving dielectric tape. The first generator was developed by the American physicist Robert van de Graaff in 1998 and made it possible to obtain a potential difference of up to 80 kilovolts. In 1931 and 1933 he also built more powerful generators, allowing to reach a voltage of 1 million and 7 million volts, respectively.
Operating principle
Thumbnail creation error: File not found
Generator diagram, see text for explanations
A simple Van de Graaff generator consists of a dielectric (silk or rubber) tape (4 in the figure “Generator Diagram”) rotating on rollers 3 and 6, with the upper roller being dielectric and the lower one being metal and connected to ground. One of the ends of the tape is enclosed in a metal sphere 1. Two electrodes 2 and 5 in the form of brushes are located at a short distance from the tape at the top and bottom, and the electrode 2 is connected to the inner surface of the sphere 1. Through the brush 5, the air is ionized from the high voltage source 7, formed positive ions under the influence of the Coulomb force move to the grounded roller 6 and settle on the tape, the moving tape transfers the charge inside the sphere 1, where it is removed by brush 2, under the influence of the Coulomb force the charges are pushed to the surface of the sphere and the field inside the sphere is created only by an additional charge on the tape. Thus on outer surface sphere accumulates an electric charge. The possibility of obtaining high voltage is limited by corona discharge, which occurs when the air around the sphere is ionized.
Modern Van de Graaff generators use circuits made up of alternating metal and plastic links instead of tapes and are called pelletrons.
Application
Historically, Van de Graaff generators were originally used in nuclear research to accelerate various charged particles. At present, their role in nuclear research has diminished as other methods of particle acceleration have developed.
They continue to be used to model the processes that occur when lightning strikes, to simulate lightning strikes on the ground.
In literature
In the novel by E. L. Voiskunsky and I. B. Lukodyanov “The Crew of the Mekong”, the Van de Graaff generator is used to impart permeability to solids.
A photo
Van De Graaff Gen 03.jpg
Van de Graaff generator
Van De Graaff Gen 04.jpg
generator without metal sphere
Van De Graaff Gen 05.jpg
Top roller and combs
Van De Graaff Gen 06.jpg
Bottom roller and combs
see also
- Van der Graaf Generator (English progressive rock band)
Write a review on the article "Van de Graaff generator"
Notes
| The most famous formula from general relativity is the energy-mass conservation law | This article in physics is a stub. You can help the project by adding to it. |
An excerpt characterizing the Van de Graaff Generator
“The dangerous ones don’t live here, we haven’t had them for a long time. I don’t remember how long ago... – came the answer, and only then we noticed that Veya was not with us, but Miard was addressing us...Stella looked around fearfully, apparently not feeling too comfortable with our new acquaintance...
“So you don’t have any danger at all?” I was surprised.
“Only external,” came the reply. - If they attack.
– Does this happen too?
“The last time it was before me,” Miard answered seriously.
His voice sounded soft and deep in our brains, like velvet, and it was very unusual to think that such a strange half-human being communicates with us in our own “language” ... But we are probably already too used to various, transcendent miracles, because after a minute they freely communicated with him, completely forgetting that this is not a person.
- And what - you never have any, no trouble ?!. The little girl shook her head in disbelief. “But then it’s not at all interesting for you to live here! ..
It spoke the real, unquenchable Earthly "thirst for adventure." And I understood it perfectly. But for Miard, I think it would be very difficult to explain this...
- Why is it not interesting? - our "guide" was surprised, and suddenly, interrupting himself, he pointed up. – Look – Savii!!!
We looked up and were dumbfounded.... In the light pink sky, fabulous creatures soared smoothly!.. They were completely transparent and, like everything else on this planet, incredibly colorful. It seemed that wonderful, sparkling flowers were flying across the sky, only they were incredibly large ... And each of them had a different, fantastically beautiful, unearthly face.
“Oh-oh.... Look-and-those... Oh, what a marvel...” Stella, completely stunned, said in a whisper for some reason.
I don't think I've ever seen her so shocked. But there really was something to be surprised... In no, even the most violent fantasy, it was impossible to imagine such creatures!.. They were so airy that it seemed that their bodies were woven from a shining mist... , spraying sparkling golden dust behind him ... Miard "whistled" something strange, and the fabulous creatures suddenly began to smoothly descend, forming a huge "umbrella" above us, flashing with all the colors of their crazy rainbow... It was so beautiful that was breathtaking!
The mother-of-pearl-blue, pink-winged Savia was the first to land on us, having folded her sparkling wings-petals into a “bouquet”, she began to look at us with great curiosity, but without any fear ... It was impossible to calmly look at her bizarre beauty, which attracted like a magnet and wanted to admire it endlessly ...
– Do not look for a long time – the Savii are fascinating. You won't want to leave here. Their beauty is dangerous if you don't want to lose yourself,” Miard said quietly.
“But how did you say that there is nothing dangerous here?” So it's not true? Stella was immediately indignant.
“But this is not the kind of danger that needs to be feared or that needs to be fought. I thought that's what you meant when you asked, - Miard was upset.
- Come on! We seem to have different ideas about many things. It's normal, isn't it? - "nobly" reassured his baby. - Can I talk to them?
- Speak if you can hear. - Miard turned to the miracle Savia, who had come down to us, and showed something.
This is a high voltage generator, its mechanism of operation is based on the electrification of a moving dielectric tape. It was first created in 1929 in the USA by physicist Robert Van de Graaf and gave a potential difference of up to 80 KV. In 1931, he also developed a device that generates 1 million, and two years later - 7 million volts.
It is known that during friction different materials each other you can get an electric charge, which attracts all sorts of small pieces of paper, dust and even deflect a stream of water. For example, we use PVC sewer pipe and sock, works no worse than the famous ebonite stick. Any substance consists of positively charged atomic nuclei and negatively charged electrons that revolve around them. Usually in a substance, positive and negative charges are equal, so the total zero, such a body is not charged. But when the sock touches the pipe, the electrons move from the sock to it, because the electrons are better attracted to its molecules.
Friction is a way to bring as many molecules into contact as possible, so during the experiment it is better to press down on the toe with more force. But not everyone realizes that in a simple way a voltage of 1000 V is reached; to verify this, it is recommended to do the experiment in absolute darkness, for example, by locking yourself in a room without windows. And observe flashes of discharges that occur when the sock is rubbed against the pipe.
The Van de Graaff generator also receives a charge due to the contact of two materials with each other, but it can receive much more voltage. When arranged, it is quite simple. An engine is fixed at the bottom of the generator, it is needed to rotate special tape, on the axis of the engine you need to fix something that, when in contact, charge the tape. We tried a whole bunch of materials to put on the axle, as well as several options for tapes. Martens' medical bandage worked best as a tape, and as a result, pieces of the same PVC pipe were put on the axis, which attracts electrons well, being negatively charged. A positively charged tape, rotating, carries its charge up, and it accumulates on a metal ball more and more. If you want the ball to become not a plus, but a minus, just stick your fingers into the pipe, the skin gives off electrons during friction. The voltage on the ball accumulates really high, judging by the size of the penetrating lightning, 100,000 V is accumulated. Cool generators created using Van de Graaff technology can generate millions of volts and are used in physics to accelerate particles to high energies.
Why does the tape always only bring charge to the ball, and never carry it away? To answer the question, you need to understand one important property conductors, because the ball, unlike the tape, is specially made of metal, a well-conductive material. Explanation for the layman, savvy dudes themselves will read about the Gauss theorem and screening.
Suppose there is a piece of metal, and a charge somehow got inside it, let it be a bunch of negative electrons, however, if it is metal, then it won’t even take a split second, as it won’t be there anymore, because it’s a bunch of electrons, they are all different repel each other. Quickly, all the excess charge will be smeared on the outer wall of the metal very, very thin layer, i.e. always accumulates on the outer surface of the conductors. Therefore, the tape cannot take a charge from the ball, it simply does not exist inside. This is the basic principle of the Van de Graaff inventor's generator. The whole trick is that we bring the tape from the inside of the ball, and not from the outside.
The ball was made from two salad bowls bought from Ikea. Inside is a bicycle sleeve, on which the tape is held, freely rotating. The charge from the tape to the ball gets either through the sleeve or with the help of an additional wire brought as close as possible to the tape. At the end it is divided into many small sharp conductors. The fact is that the charge drains much better through the air on the tip. The ladle into which lightning strikes is grounded through the body of a homemade generator.
The Van de Graaff generator was invented in the first half of the last century. It has been used for various purposes, including nuclear testing. Over time, the range of applications has narrowed significantly. Nowadays, you can freely purchase it and demonstrate to children the levitation of various objects. It is also possible to build a generator yourself, then it will become a good educational model for conducting various experiments.
Do you want to become a wizard? Take the regular plastic bag, cut off the two ends and tie tightly with a thread - you should get a bow. After that, rub a simple plastic ruler on something woolen and bring it to the bow: the real flight will begin!
A ready-made "magic wand" and figures with which you can do similar tricks can be bought in stores.
But toys that copy the model of the generator are powered by rechargeable batteries. If you press the button, an electrostatic charge arises at its end, passing to the figures, repelling the charges from each other. The figurine has a certain cutout, it is inflated and the volume increases. When the charge is weak, you need to press the button again.
Excursion into history
Of course, the electrostatic generator is not only a toy for children. An American scientist created his product while conducting serious research in the field of atomic physics. The first demonstration sample saw the world in 1929, it was small in size. The tribogenerator looked more impressive, which was installed on the rails of airships. The structure consisted of two pillars, on top of which were attached hollow aluminum spheres with a diameter of 15 feet.
In 1931 and 1933, two installations were built, the power of which reached incredible values - up to seven million volts, and the first sample - only 80 kilovolts.
Inside, there is a rotation of the vertical dielectric paper tape. The roller located at the top is a dielectric, and the one at the bottom is metal and is connected to the ground. The brush electrode of the sphere is responsible for the removal and supply of charge, which is evenly distributed in it. Ionization occurs near the bottom electrode air masses, useful will settle on the tape, and top part will start charging.
To obtain a high potential difference of linear particle accelerators (it was for this purpose that a similar generator was developed), two spheres with unequal charges are used. One contains the positives and the other the negatives. At a certain concentration, an electric charge jumped. It was he who was investigated. The voltage could be several million volts.
Previously, devices were used in nuclear research, particle acceleration. After the emergence of other methods for solving these problems, their use has been significantly reduced. Nowadays, such generators are used for simulation. For example, they help to simulate natural gas discharges. But the tapes have now been replaced on a chain with plastic and iron links placed alternately.
DIY manufacturing
The model is easy to assemble by yourself, using improvised materials. A do-it-yourself generator will be made up of elements such as:
Please note that all components must be completely dry, at the same level as the air temperature in the working room. Otherwise, the model may not work at all or give too weak impulses. Detailed scheme and a video on the creation of the Van de Graaff generator can be found on the Internet.
To do homemade generator, drill a hole in the board that will become the base . Select desired diameter drill, it should be in the shape of a pen. Then make a couple of holes on the tube: the first on top, the second on the bottom - for pastes, then two more - above the first and perpendicular to the bottom.
Next, the pastes are cleaned of ink. A piece is cut according to the diameter of the pipe. The paperclip straightens out, it should protrude 1 centimeter beyond the tube. Scotch tape is used as the base of the dielectric tape. They should glue the gum so that it is sticky on both sides.
Pre-prepared elements are collected.
Brushes are added, charge is collected in them. From below, the brush must pass through the hole, the tip is left fluffy. The brushes are close to the elastic, but do not touch it. The top is threaded through the nearest hole. Then the non-working light bulb is tightly glued with foil. The top wire is tightly attached to the foil. The light bulb is left at the top of the structure.
Generator ready for use.
Experiments with a generator
The device must be discharged after each use, be careful in work, because electric shock can lead to death.
The Van de Graaff generator was invented at the beginning of the twentieth century. It was used for various purposes, in particular, for nuclear research. Later, the use narrowed. Today you can buy it as a toy and demonstrate to children the levitation of various objects. You can also build a generator yourself. Then it will become an excellent training model with which various experiments are carried out.
Children's tricks
Do you want to create "magic"? Take a plastic bag, cut off both ends and tie with a string to make a bow. Then rub the usual plastic ruler well on the woolen thing and bring it to the bow: the flight will begin ...
Ready " magic wand” with figures with which you can do such tricks, you can also buy in the store.
But the easiest option to see the "magic" is just to pet the cat. Then you can both feel and see the resulting static electricity.
But a toy that repeats the design of the Van de Graaff generator works on battery. When the button is pressed, an electrostatic charge is created at the tip. Therefore, the figurine adopts it, and charges of the same name begin to repel each other. Since the figurine is carved in a certain way, it "inflates" and gets volume. If the charge weakens, then you just need to press the "magic" button again.
A bit of history
Of course, the Van de Graaff generator is not only children's toys. The physicist himself created his brainchild to conduct serious research in the section of atomic physics. The first demonstration sample was made in 1929. He was small size. More impressive dimensions were obtained by the Van de Graaff generator, mounted on rails for airships. The model consisted of two pillars topped with hollow aluminum spheres fifteen feet in diameter.
The installations built in 1931 and 1933 reached a power of seven million volts. But only a charge of up to eighty kilovolts was provided by the first Van de Graaff generator.
Operating principle
A paper dielectric tape rotates vertically inside. The roller located at the top is a dielectric, and the lower one is made of metal and is connected to the ground. The brush electrode in the sphere removes and supplies the charge, which was distributed evenly in the sphere. Near the electrode below, the air is ionized, beneficial ions settle on the tape, and that part of it that goes up is charged.
In order to obtain a high potential difference in linear particle accelerators (for which these generators were needed), two spheres with different charges were used. In one of them, positive ones accumulated, and in the other, negative ones. When the concentration reached a certain level, an electric discharge jumped between them. It was he who was investigated. The voltage here reached millions of volts.
Earlier devices were used for nuclear research and particle acceleration. After other methods of acceleration appeared, they began to be used much less frequently in this area. Currently, the Van de Graaff generator is mostly used for modeling. For example, with its help, natural gas discharges are imitated. Instead of tapes, installations often use chains consisting of plastic and iron links alternately.
What you need for self-assembly of the device
The model is easy to build yourself from improvised means. The Van de Graaff generator, assembled with your own hands, consists of the following components:
- pencil
- pvc pipe cutting;
- gum;
- paperclips;
- aluminum foil;
- engine from a toy;
- non-working light bulb;
- dry pastes from the handle;
- nine volt batteries;
- adhesive tape;
- wires;
- boards.
All elements must be dry, just like the air in the room. Otherwise, the design simply will not work or will, but very weakly.
This is what the Van de Graaff generator will turn out to be. The photo below shows what the model should look like.
How the generator is made independently
First, a hole is drilled on the plank, which will become the base of the structure. The drill is selected with a suitable diameter, the shape is in the form of a pen. Then two holes are made on the tube: top and bottom, for pastes. Make two more holes: one just above the top, and the second - perpendicular to the bottom.
Next, the paste must be completely cleaned of ink. Cut out a piece corresponding to the inner diameter of the pipe. They take a paper clip, straighten it and cut off a piece of sufficient length so that it protrudes a centimeter from the tube.
Dielectric tape is made from adhesive tape. The gum is glued so that both sides are also sticky.
Prepared elements are collected.
Add brushes that collect charge. At the bottom, the brush passes through the hole, and the tip is made fluffy. The brushes should be close to the elastic, but not touching it. The top is threaded through the hole at the top.
After that, with the help of aluminum foil, a non-working light bulb is pasted over. The top wire is attached to the foil. The lamp is inserted on top of the structure.
The training Van de Graaff generator is ready.
Experiences
If you attach several threads to the upper electrode and bring your hands closer, they will “stand on end” and wrap around your fingers. Try experimenting in the dark.
To get a more powerful voltage, two generators are connected.
A good option for experiments would be a Leyden jar.
The most famous experience is the one in which the hair stands on end. To do this, you need to stand on wooden board or plywood. The hand is placed on the sphere (while the generator must be turned off so as not to be shocked). After turning on the device, a spark will pass, as a result of which the hair will stand on end.
The generator should be discharged after each use and handled with extreme caution, as the current can become deadly to humans.