Van de Graaff device and common sense in physics ….

[sorin]

Van de Graaff device and common sense in physics ….

The working principle for Van de Graaff device is analyzed again in this material:

http://elkadot.com/index.php/en/books/electromagnetism/van-de-graaff-device

The actual explanation contradicts all we know about triboelectricity. It is impossible for the same belt to come into contact with two identical rollers and to deliver a positive charge to a sphere and a negative charge to another sphere. Either triboelectric series, either actual explanation for VDG device is nonsense.

More than that, it is impossible to transfer a same type of charge from a body carrying a smaller charge to another body carrying a greater charge. Therefore the maximum charge accumulated on spheres should be equal with amount of charge generated in contact or friction process. Actual physics it is not able to explain how is possible to accumulate a huge charge on the sphere during belt rotation in contradiction with all known concepts of physics.

The Van de Graaff device with a charge injection system does not need any comment. Why don’t we inject directly the charge over the sphere and arrive to billions of volts and it is preferred to inject it on a belt and carried further by the belt…..?

The old material is still available as pdf file on the site and in fact the new material is only a refined presentation of it.

Best regards,

Sorin Cosofret

[John Cuthber]

A few points.

The VdeG works.

The way in which it works is often poorly explained.

The way in which it works is well understood by science.

It's not got a lot to do with triboelectricity (I agree that triboelectricity isn't very well explained- but that's not the point).

 

The biggest single misunderstanding you seem to have is that you have not realised that the motor does work on the belt because it is pushing (for example) a positive charge towards the positively charged top of the generator.

In dong so, it moves a charge to a point here the potential is greater.

that's how it makes a higher voltage.

So the assertion in that pdf "Instead of spraying the charge on the belt, and after that the charge is again collected from the belt and moved on a sphere, a greater yield and a higher potential can be achieved if the sphere is removed from VDG and the charge is sprayed directly on the sphere as in fig. 14."

doesn't make sense.

 

BTW, are you the same guy who didn't understand physics here?

http://www.scienceforums.net/topic/35321-electric-current-and-electrolysis

Edited May 31, 2015 by John Cuthber

[swansont]

!

Moderator Note

 

Let's confine conversation to the physics discussed here, lease.

 

That includes not linking to promote you own site, sorin.

 

[Sensei]

It is impossible for the same belt to come into contact with two identical rollers and to deliver a positive charge to a sphere and a negative charge to another sphere.

"Positive charge" is absence of electrons.

And "negative charge" is abundance of electrons.

 

Electrons from one sphere are harvested ("positive charge" sphere), and gathering on another sphere.

 

it is impossible to transfer a same type of charge from a body carrying a smaller charge to another body carrying a greater charge.

I think so you're making mistake taking just absolute quantity of charges, without taking into account also area and/or volume.

 

Imagine you have metal ball with radius 1 cm, with 1 Coulombs charge (6.24*10^18 electrons),

and another same metal ball with radius 10 cm, with 2 Coulombs charge.

Charge on 2nd ball is higher than charge on 1st ball obviously.

But charge density on 1st ball is higher than charge density on 2nd ball.