From Wikimedia Commons, the free media repository. Robert J. Van de Graaff. Subcategories This category has the following 2 subcategories, out of 2 total. Media in category "Van de Graaff generators" The following 89 files are in this category, out of 89 total.

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The rubber band steals electrons from the glass tube, leaving the glass positively charged, and the rubber band negatively charged. The second trick involves the wire brushes. When a metal object is brought near a charged object, something quite interesting happens. The charged object causes the electrons in the metal to move.

If the object is charged negatively, it pushes the electrons away. If it is charged positively, it pulls the electrons towards it. Electrons are all negatively charged. Because like charges repel, and electrons are all the same charge, electrons will always try to get as far away from other electrons as possible. If the metal object has a sharp point on it, the electrons on the point are pushed by all of the other electrons in the rest of the object.

So on a point, there are a lot of electrons pushing from the metal, but no electrons pushing from the air. If there are enough extra electrons on the metal, they can push some electrons off the point and into the air.

The electrons land on the air molecules, making them negatively charged. The negatively charged air is repelled from the negatively charged metal, and a small wind of charged air blows away from the metal. The same thing happens in reverse if the metal has too few electrons if it is positively charged. At the point, all of the positive charges in the metal pull all the electrons from the point, leaving it very highly charged.


After we understand the third trick, we will put all of the tricks together to see how the generator works. We said earlier that all electrons have the same charge, and so they all try to get as far from one another as possible. The third trick uses the soda can to take advantage of this feature of the electrons in an interesting way.


We can keep adding as many electrons as we like to the inside of the can, and they will always be pulled to the outside. The motor moves the rubber band around and around. The rubber band loops over the glass tube and steals the electrons from the glass. The rubber band is much bigger than the glass tube. The electrons stolen from the glass are distributed across the whole rubber band. The glass, on the other hand, is small. The negative charges that are spead out over the rubber band are weak, compared to the positive charges that are all concentrated on the little glass tube.




The top brush is connected to the inside of the soda can. It is positively charged, and so attracts electrons from the can. The positive charges in the can move away from one another they are the same charge, so they repel, just like electrons. The positive charges collect on the outside of the can, leaving the neutral atoms of the can on the inside, where they are always ready to donate more electrons.

The effect is to transfer electrons from the soda can into the ground, using the rubber band like a conveyor belt. It doesn't take very long for the soda can to lose so many electrons that it becomes 12, volts more positive than the ground. When the can gets very positive, it eventually has enough charge to steal electrons from the air molecules that hit the can. This happens most at any sharp points on the can.

If the can were a perfect sphere, it would be able to reach a higher voltage, since there would be no places where the charge was more concentrated than anywhere else. The places on our soda can where the curves are the sharpest are where the charge accumulates the most, and where the electrons are stolen from the air. Air ionizes in an electric field of about 25, volts per inch. Ionized air conducts electricity like a wire does. You can see the ionized air conducting electricity, because it gets so hot it emits light.

It is what we call a spark. Since our generator can draw sparks that are about a half inch long, we know we are generating about 12, volts. Zavisa Static Electricity To understand the Van de Graaff generator and how it works, you need to understand static electricity.






Van de Graaff Generator



gerador Van de Graaff

A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate electric charge on a hollow metal globe on the top of an insulated column, creating very high electric potentials. It produces very high voltage direct current DC electricity at low current levels. It was invented by American physicist Robert J. Van de Graaff in A tabletop version can produce on the order of , volts and can store enough energy to produce a visible spark. Small Van de Graaff machines are produced for entertainment, and for physics education to teach electrostatics ; larger ones are displayed in some science museums. The Van de Graaff generator was developed as a particle accelerator for physics research; its high potential is used to accelerate subatomic particles to great speeds in an evacuated tube.

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