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Author Topic: What is the mechanism of charge movement behind a Van der Graff device?  (Read 8472 times)

Offline sorincosofret

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What is the mechanism of charge movement  behind a Van der Graff device?

If the VGD sphere and brushes are removed, the mechanism remaining is a simple belt moving on two rollers.
The proposed experiments and discussion focuses on the following question:
Do we count a charge movement due to the belt rotation over the rollers?
From triboelectricity it is known that rubbing two materials, one became ,,positively “ and the other ,,negatively “ charged.
In our case let’s suppose that in the lower roller, the friction of the belt with roller produce a positive charge on the belt. In the same time, a negative charge must appear on the roller. The positive charge is carried by belt on the superior roller. Here there are more possibilities.
The positive charge is neutralized due to the second roller and in this case between the second roller and belt an opposite charge must be generated compared with lower roller (fig.1 ). More precisely in this case due to the friction, the belt is charged negatively (and compensates the positive charge carried by belt) and the  roller becomes positively charged.





Figure 1.

But in this case, if the brushes are fixed on the rollers, it should be detected a charge movement between upper and lower roller.
In time, it can be demonstrate that in few hours huge opposite charges accumulate on the both roller and due to the enormous attraction force the VDG disintegrate.
Supplementary, this explanation enters in contradiction with already known experimental principle of charge distribution due to the friction. It is impossible to have between two identical materials an opposite distribution of charge only due to a difference of height (the upper roller is with 50 cm upstairs).

Another possibility is to have the same charge type production during the upper roller friction.
In this case, the entire belt becomes positively charged, and the rollers become negatively charged (fig. 2). In time, huge amount of identical charges accumulate on the rollers and huge amount of opposite charge accumulate on belt. It should appear strange effects only due to the belt rotation. Discharge between belt and roller or belt and air should appear.



Figure 2.

Both of these possibilities enter in contradiction with already presented mechanism for the VGD device. In VDG device the electrodes are charge collectors. So it is impossible to imagine how the lower roller produce a positive charge on the belt and the upper identical roller produce a negative charge on the belt (figure 3).  Supplementary in all known scientific books, the rollers remain uncharged. How is possible that? Does the low of charge conservation not work in this case?




Figure 3.

My VDG device produce ,,positive potential” on the sphere and the sign was determined using a electron source (CRT)  as reference and considering that a body charged by contact method with electrons coming from CRT will have a negative potential.

In the actual VDG working mechanism there are other fictitious ideas.
There is a certain distance between brushes and belt. Actual explanation that air between belt and brushes becomes ionized is not a good solution for insuring the transfer of charge. Of course air become conductor over a certain difference of potential and the phenomena of air conduction manifests by easy to observe sparks. In case of VDG it should appear a ,,gun effect” when the device is working. More precisely the charge accumulate on the belt and from time to time sparks appear between belt and brushes like an armed gun who fire with a specific rate. This effect does not appear in ,,normal” VDG working conditions. It can appear, but these are due to a problem in VDG working.
The mechanism of charge transfer between belt and brushes can be proved if the entire system is placed in an advanced vacuum. In this case, in absence of ionized air, the charge transfer should be diminished and consequently the intensity of ,,electric current” produced by VDH should decrease in comparison with atmospheric working condition.   In the proposed theory, the presence or absence of dry air between brushes and belt does not play any significant importance ( the current will be quite the same).
Another problem regards the mechanism of this transfer of charge. It is assumed that with every belt rotation a small quantity of charge is generated by friction and this charge is spread over the sphere. But how is possible this event?
After few minutes of working, the sphere surface arrive to a huge potential, and the small quantity of charge found on the belt should not be able to be overloaded on the sphere. Normally, after short time of VDG working, the charge transfer should flow in opposite direction, because there is a normally tendency to equalize the charges. 

The third possibilities and the most ,,common sense” regard the non-generation of charge during belt rotation.  A belt can rotate on two rollers for weeks without any air ionization and charge accumulation. The proposed theory is based on this non-charge generation. I’ve seen that my explanations are considered stupid so I will try to post here only the experiments or actual defective explanations.

Different and simple variants of experiments were made in order to prove the actual orthodox explanation and the new proposed mechanisms. The experiment regarding the current modification under vacuum condition is not made yet.



 

lyner

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I think you have been reading the 'Noddy' version of how it works. Where do you get your information?
The 'correct' version is that the VDG works by electrostatic induction.
Look it up.
A bit more 'receive' and a bit less uniformed 'transmit' might help, sorin.
 

Offline sorincosofret

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Please give me a reference with a good presentation about VDG working principle.
 

lyner

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You can use Google as well as I can. I only remember that there were a number of articles - of various depths - and that some of them give the correct treatment.
The simple explanation even suggests that you 'spray' charge onto the belt from a HT generator.
Why go looking for non-charge-conservation when it clearly can't be happening.
I think your problem is that you enter into all these topics, determined to prove the existing theory is wrong.
With respect, I don't think you have the grounding to do that.
« Last Edit: 04/11/2008 16:59:29 by sophiecentaur »
 

Offline sorincosofret

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I have read the internet and all VDG device presentation are made after the same template. The most comprehensive explanation seems to be on wikipedia. There is explained a variant of VDG having a ,,charge" injection in the lower part and catching ,,this charge" in the upper part.
This is not the original VDG device. Of course, it is not a problem to explain this improvement.
The foundation of a science must be established on basis of simple experiments. A complicate and detailed experiment is not able to reveal the principle which lay behind.
If Kepler had a better precision in his measurements, I have doubt that he could discover the lows of planet motion.
Of course, after the foundation is well established, it is necessary for a exact science to go in the precision and details of measurements.
For the moment I'm not interested in precision.
In the same time, as I said already, I had to make some payments so, the actual theory will be changed on basis of simple 10 euro experiments.
Electric and electronic experiments are my speciality ... and as  you see I'm at electrostatic experiments...
After that, the ,,true physics experiments" will be proposed.
Whom must I ask permission for entire physics and chemistry foundation change?
Why you insist on non-charge conservation. I'm sure there is no charge movement. How can a low be discarded when this law does not apply to the case?
I have made a simple discussion, and I have presented some possible explanations.
I expect from actual experts to recognise that actual theory is not able to explain the oldest  and simplest experiment in electricity. Because the charge production by friction is known from antiquity.
After that, who wants to use the new proposed theory should pay for this. The other can remain with actual explanation.

 

lyner

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Why do you use the term "charge production"? What occurs is Charge Separation.
Where are you suggesting that a bucketful of charge will be available without an equal and opposite bucketful?

If the Ball acquires a surplus of electrons, they have come from the Earth and left behind a surplus of protons. All the VDG does is to achieve a separation of charge onto a ball which has a low capacity (C) to Earth.
V=Q/C
Low C gives high V.
If you did the same thing with a capacity of a few microFarads instead of about 100picoFarads, it would take hours and hours to reach the high voltage at the rate the belt carries charge.
This would be a lethal piece of kit, of course.
Does this not satisfy you?
You are, as usual, trying to be controversial with no grounding.
 

Offline sorincosofret

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I'm not controversial, but I can't see the relevance of your message.
I ask you some simple thing to be explained.
When two materials are rubbed one another, both materials charges (by transfer of electrons as you say because there is no charge creation from nothing), or only one of them become charged?
Please look in all VDG description and you will see that a belt is rubbing a roller and the belt becomes charged and the roller not.
When the same materials are rubbed one another, can exist today a sign charge distribution and tomorrow another charge distribution (more precisely a piece of wool can become today negatively charged and tomorrow positively charged when is rubbed on the same wood material?)?
Look at the same known VGD device in every ,,good" book and you will see that a difference of half of meter altitude change completely the triboelectric series.
Do you consider this as a normal situation in physics?
 

lyner

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The problem is, sorin, that your whole manner is controversial. You constantly appear to be challenging and doubting instead of 'enquiring'. You are clearly not daft - it's more the way you approach things. Try studying other contributors' styles if you want a better reaction.
Quote
\belt becomes charged and the roller not.
The roller does become charged. It becomes densely charged after a number of revolutions by friction / contact-separation. The belt, as it is moving, has the charge spread over it. As sections of the belt approach the charged roller, they become polarised and the comb neutralises the charge from one side, leaving the belt charged. This is what is called electrostatic induction. If you google "Electrophorus" you will see the simplest machine for showing this effect. You charge a plastic mat once and can repeatedly charge a metal plate by following a simple action.
The charges are carried up and the same thing happens at the top.

see http://www.eskimo.com/~billb/emotor/belt.html

Take two substances and rub them together. The charge signs produced are pretty consistent. Have you any contrary evidence?
 

Offline Bored chemist

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"Please look in all VDG description and you will see that a belt is rubbing a roller "
Actually I'm not sure about that. To a good aproximation the belt and roller have the same speed so there's very little rubbing.
Real V de G generators (rather than toy ones) have a high voltage power supply that feeds  charge onto the belt.
 

lyner

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Quote
there's very little rubbing.
You don't really need rubbing. You only need to put them together and take them apart - like with clingfilm - to get some charge separation. In any case, there's always some slip as the belt is floppy.

The high voltage generator can't behave as simply as the diagrams all suggest or everything would quickly jack itself up to the generator voltage and there would be no more charge flow. There must be something more subtle happening, I think.
« Last Edit: 05/11/2008 20:54:04 by sophiecentaur »
 

Offline sorincosofret

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In this case a new physics must be described. In a part of physics is described how a electron is emitted at high temperature ( Eddison effect) or due to a excitation energy which is quite consistent.
In another case, the same electrons are passing from a material to another only due to the geometrical form of the object (sharp), even there is no reason for this charge transfer.
Your reference link ( http://www.eskimo.com/~billb/emotor/belt.html
) is only the trial of a person to explain the VDG principle, because he observed the inconsistency of accepted explanation.
This does not mean he has right.
If the lower brush is removed, you will be in a situation presented in another post and his explanation does not work.
Another simple case> connect the lower brush to a certain object. How long do you think it is possible to take charge from it?
Make a simple math and you will see that after few minutes the VDG should stop to work.
In the same time, he was underlined that VDG works with the second roller made from another type of material (generally metallic). MY VDG works with both rollers made from the same material. How is applying his explanation in this case?
A detailed analysis will show that a charge injection will change some things in the triboelectric process, but is not the case to insist here.
Original Van der Graff are without any injection charge on the belt. The ,,charge" injection modify the mechanism but again the actual explanation is ruled out.
 Of course, I'm agree with you:,,There must be something more subtle happening, I think.".
This will be described in the book.
It is not the case to ,,fix" the attention to much on the VDG device. There will be other posts more interesting...




« Last Edit: 06/11/2008 04:39:12 by sorincosofret »
 

Offline Bored chemist

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"In this case a new physics must be described."
Bollocks.
 

Offline sorincosofret

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The procent of ,,bollocks" in actual orthodox theory has increased from a 90% to a 95%.
What waste of papers and effort ...for nothing..
 

lyner

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Quote
second roller made from another type of material (generally metallic)
Actually, the upper roller material in a simple system is not very  important. The charges will be picked up by the top comb and move to the outside of the sphere because of mutual repulsion.

The 'more subtle' statement about the EHT generator method is not an open door for you to look for a new Physics. The probable explanation is that the EHT generator merely provides a high charge density near the belt which enhances the inductive charging of the belt. Occam's Razor is always worth applying when you can.
BTW, are you using a computer to do your translation?
 

Offline sorincosofret

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OK, you have expressed your opinion, I have expressed mine. Let's leave the time to decide the truth.
I don't use a computer, only the spell check from Naked.
 

lyner

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So why not use the right / accepted words?
Your English is, of course, much better than my ability in your language but my comment is still valid.

Do you understand the concept of inductive charging?
 

Offline sorincosofret

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I accept the existence of phenomena of so called ,,inductive charging". But when the source of this inductive charge disappear, the effect should disappear. In case of VDG , a single brush produce enough potential to be measured like a current or a gas tub flickering.
When I connect the lower brush to a neutral object of course it is absurd to think that a neutral object produce inductive charge.
Even I admit that fact, after few minutes, the VDG should stop to work, because the opposite charge remaining on the object connected to lower brush will be huge.
You didn't make the entire analysis of situation"
variation of intensity due to the presence or absence of air between brush and belt;
how a small charge on the belt overcharge a greater charge on the sphere.
 

lyner

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Of course you need an initial charge displacement for inductive charging to work but when does this source 'disappear'?

What is your second paragraph supposed to mean? The brush needs to be held  at neutral potential (Earthed) for the induction to work. You clearly don't understand the process or you wouldn't have made that comment.
The limit to the achievable voltage on the VDG is set by corona and leakage through the frame.

Quote
how a small charge on the belt overcharge a greater charge on the sphere.
In every one of your posts you demonstrate your limited knowledge.
What makes charge flow is Potential Difference, not how much charge is each side. The charge on the sphere is on the outside and the PD between belt and the inside of the sphere is in the direction to make the charge flow onto the drum.
How can you have the nerve to write such stuff when you know so little about the subject?
How can you be so arrogant?
 

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