SIMPLE THEY GO OF GRAAFF

In the projects that we showed in this same virtual magazine we made equipment that take the high voltage from a television set. Now we will construct tiny equipment that can generate up to 12 000 volts from a tin of soda water and a rubber band (league). This equipment is called Van de Graaff, it is possible to be found more in the science museums because it can give up to 500 000 volts or. Ours he is more modest but it can produce chsipas of about 2 centimeters in length, although the amperage (the current) is very little, reason why equipment, with its 12 000 volts is not dangerous. It produces static electricity. Materials that you need

  • An empty soda water tin
  • a small nail
  • A league (rubber band) great of 1 or 2 cm in width and of 6 to 10 cm in length
  • A fuse of some 5x20 millimetros
  • A small motor of DC (of a toy)
  • A glass of plastoform (or of parafinado paper)
  • Instantaneous glue
  • Two cables of about 15 cm in length
  • Two pieces of tube of plastic pipe of 3/4 of inch PVC of 5 or 7 cm in length
  • It connects of 3/4 of PVC
  • A connector T of 3/4 PVC
  • Sticky tape
  • A wood block
As much material! You do not worry, gives a glance to the photos and you will realize the simple thing that it is to make equipment.

We will initiate by the part of down.

First that there is to do is to cut a piece of 5 to 7 centimeters of a tube of 3/4 of inch of PVC and is thrown out of reach it to a wood base. This piece will hold the generator and it will allow us to clear easily as well as to replace to the rubber band (league) or to make adjustments.

PVC connector T will hold the small motor. In order to hold to the motor he is better to surround something of insulating tape around. The axis can be left as it is, but is better to put something to him of insulating tape or tubito of plastic so that it acts as pulley for the rubber band. Soon we perforated a hole to a side of connector T of PVC right under the pulley of the motor. This hole will be used to hold to the “brush? inferior that is simply bare cable in an end and that is almost touching the rubber band in the pulley.

As it is seen in the photo, the bare cable subjects in if place with sticky tape or glue.

The rubber band is placed in the pulley and it is left hangs of connector T.

Now, we cut about 8 to 10 cm of tube of 3/4 of PVC. This it will go on connector T, with the rubber band in the interior. We use pin to hold the rubber band. The length of the tube must be of the same length that the rubber band. This does not have to be very prim because the friction will avoid that the motor turns.

We cut to the glass of plastoform from the base, leaving some 2.5cm and cut a hole of the same diameter that the tube in the base and to means. We introduce tube PVC by this hole.

Soon perforate three holes to us in connects of PVC. Two of these must be in opposite places because they will hold pin that will act of axis for the rubber band. The third hole is between the other two and will hold to the “brush? superior, the one that, like the one down is so close that “almost? it touches to the rubber. The brush superior subjects to the tube of PVC union and it connects is put in the tube of 3/4 on the support of glass of plastoform. The rubber band gets drunk by connects and is maintained it in its place with the nail. The cable is peeled and it occurs some him returned so that the alambritos do not separate much.

The other end of the cable subjects within the soda water tin so that electrically it is connected to the “brush?.

We need a small tube glass that works as pulley of low friction and as “triboeléctrico? complement of the rubber band, both us servirián to generate static electricity by friction. The glass and the rubber are very good generators of electricity. The tube is obtained of fissile an electrical one. The metallic ends take off with a soldering iron.
They keep the small covers from metal… we will use them for another project! Tubito of glass does not have imperfections and it will not be broken easily. The following step is a little difficult: we put pin by one of the holes in the tube, soon introduces tubito of glass, later vbanda of rubber that must be on tubito of glass and finally we put pin in the orifice of the front. The rubber band must turn on tubito of glass and this to turn on pin.

Now we glued the base of the small glass in the PVC tube. He is better to use hot silicone so that it helps to that he is stable.

Now already we can use a soda water tin, these are used because they do not have corners, which diminishes the “unloading of crown?. With a blade, it cuts a hole in the base of the tin. Of the same edge of the cut in the base, one takes control to hold the bare cable of the “brush? and the tin is pressed until it touches the cut glass. Finally, we welded some cables to the motor for the batteries. They are possible to be used a pair of batteries, or a battery of 9 volts. But the battery rotates too fast to the motor and the glass tube is broken, although the obtained voltage is higher. In order to make work Van de Graaff it connects the batteries. If the “brushes? are closely together, but without touching to the rubber band, you will feel one chsipa that leaves the soda water tin when approaching the finger. It is good idea to hold with the other hand the cable of down, the brush inferior. This equipment next to the bells of Franklin can be used who sees himself in this same magazine.

How it works?

Surely that, sometimes, you rubbed a globe in your hair, soon you stuck it to the wall. If you never do it fact tries it! The Van de Graaff generator uses this same trick, as well as other two to generate the high voltage necessary to produce a spark.

The first trick

When the globe made contact with your hair, the rubber molecules tocáron the hair molecules. When touching itself, the rubber molecules attract electrons of molecules of the hair. When separating the globe from the hair, some of those electrons remain in the globe, giving him a negative load. The electrons extra in the globe repel to electrons the wall pushing to them of the surface. The surface of the wall remains with a positive charge, because there are less electrons than when she was neutral. The wall with positive charge attracts the negative globe with sufficient force as maintaining beaten it against himself. If we selected materials and we rubbed them some with the other, we can find as they remain with negative load and as with positive charge. We can take these objects in pairs and place them in a list; of most positive to most negative. This list is called the Triboeléctrica Series. The Tribo- area code means “to rub?.

The triboeléctrica Series

    Most positive
    (in this end they lose electrons)

  • asbestos
  • rabbit hair
  • glass
  • hair
  • nylon
  • wool
  • silk
  • paper
  • cotton
  • hard rubber
  • synthetic rubber
  • polyester
  • plastoform
  • orlon
  • Saran
  • polyurethane
  • polythene
  • polypropylene
  • Polyvinyl chloride (tube PVC)
  • teflon
  • silicone rubber

    Most negative
    (in this end they rob electrons)

Our Van de Graaff uses a tube of glass and a rubber band. This robs electrons of the glass tube, leaving it with positive charge, whereas the rubber remains with negative load.

In this drawing the rubber band can be seen clearly the pulleys and the “brushes? in both ends, above and down.

The second trick

The triboeléctrica load is the first trick. The second is in the wire brushes. When a metal approaches a loaded object, this one causes that the electrons in the metal move. If the object has positive charge hauls electrons, if it has negative load pushes them. The electrons have negative load. As equal loads are repelled and the electrons have all equal loads, they always try to be remotest possible some of the other. If the metal object has an end, the electrons in this one are pushed by the rest of electrons in the rest of the object. Then in an end there are many electrons pushes do from the metal, but no pushing from the air. If there are sufficient electrons in the metal, these can push other electrons towards the air. The electrons land in molecules of the air giving them a negative load. The loaded air negatively is repelled of the loaded metal negatively and a wind with negative load blows from the metal. It is called to this “unloading of crown? because a light in the form of crown can be observed. The same happens to the inverse one if the metal has very few electrons (if it has positive charge). In the end, all the positive charges in the metal haul all the electrons very leaving loaded it. the air molecules that arrive at the end lose electrons by the positive end. The air molecules are now positive and are repelled by the metal with the same load.

The Third trick

After to learn this last trtuco we will be able to understand the operation of the generator. We shelp that all the electrons have the same load and try to move away some of another as much as it is possible. The third trick uses the soda water tin to take advantage from this. If we give to the tin an electron load him, these will try to be remotest some of others as it is possible. This has the effect of which all the electrons go away to the outside of the tin. Any electron in the interior will feel the push of the other and it will move. The electrons in the outside feel the push of the tin, but not of the air that does not have load. This means that if we put electrons inside the tin, they will be hauled to the outside. We can put so many electrons as we want to the interior of the tin, all will go away to the outside.

Then how work does the VDG?

It works making work the three tricks that we have seen. The motor rotates the rubber. This goes around the glass and it robs electrons to him. The rubber band is greater than the glass tube. The robbed electrons of the glass are distributed by all the rubber band. The positive charge of the glass attracts electrons of the cable in the brush superior. These electrons load the air leaving the ends of the brush. The air is repelled by the cable and attracted the glass. But the loaded air cannot arrive at the glass, because the rubber band interposes. The loaded air arrives at the rubber and they transfer electrons to him. The rubber band arrives at the brush from down. The electrons in the empujana rubber the electrons of the cable. The electrons of the cable are moved away and they go away to earth or the person that is taking hold the cable. The ends of the brush inferior are now positive and they haul to electrons of any air molecule that touches them. This positively loaded molecules are repelled by the cable with the same load and are attracted by electrons of the rubber. When they arrive at this one, it picks up his electrons again and the rubber and the air lose their load. The rubber band is now ready to rob more electrons of the glass tube. The brush of above is connected to the soda water tin. It has positive charge and it attracts electrons of the tin, the positive charges of the tin move away some of others. Electrons of the soda water tin are transferred towards earth, using the rubber band for this. In just a short time the soda water tin it loses so many electrons that becomes 12 000 volts more positive than the conección to earth. If the tin were greater would be arrived at a higher voltage. The Air ionizes in an electric field of about 50 000 volts by centimeter. The ionized air leads the electricity as a cable. The ionized air can be seen driving electricity when so much that emits light, in this case is warmed up we called electrical spark to him.

Tricks with Van de Graaf

One of the interesting things to see with the VDG is how the equal loads are repelled. We take paper from napkin and we cut strips of this light paper. We glue with sticky tape the ends and soon we held to the Van de Graaf generator. One will see as if the soda water tin had hair. When igniting Van de Graaff, we noticed that the paper strips acquire the same load and some with the other are repelled. The strips are stopped as the hairs in the back of a cat. If we have a companion with the very thin hair, we can request that one rises to him a plastic bank and touches generator VDG, right away his hair will be stopped.

GENERATOR GOES OF GRAFFGENERATOR PLANES GO OF GRAFF - GREAT

Physics (Static Electricity)

Generator of static electricity that can get to produce more than 100 000 volts. These
planes have the explanation step by step to be able to construct to a generator with homemade materials and few tools. (Beam click in the figure for a greater image)

-    Price $US2. -     

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Armed and ready equipment to use. It enters to ours Catalogue

 

                                                                                      

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