Projects for Classic Charge Distributions

[Albertgauss]

In my most recent post, I tried to investigate the V(r) verses “r” for several charge distributions on conductive paper. The discussion there made me realize that the common conductive paper activity is not suitable for doing that. Nevertheless, I am interested in doing projects where I can find V(r) for some of the basic charge distributions so common to beginning to basic electrostatics like V(r) = kQ/r (point charge), V(r) = (λ/2πε)ln(r2/r1) for ∞ line of charge, or the finite wire, etc. Does anyone know of any real-life experiments where people actually tested out these voltage expressions? I have played around with a capacitor for parallel plates that many science education companies sell. Surely someone must have done this---even if centuries ago---since science always must always be checked. I haven’t found much just doing internet searches but if someone knows of someone who has done real V(r) to test the validity of what we get for these classic charge distributions, point me in that direction. I am willing to get all the materials and do the project. I have worked with a Van De Graaff as a point charge, but there is no easy way to measure “kQ” in that situation for a bunch of reasons I won’t list here.

 

[anorlunda]

ping @ZapperZ

How does this differ from your other thread?
https://www.physicsforums.com/threads/voltage-lab-conductive-paper-questions.984061/

 

[ZapperZ]

Summary:: Looking for labs/activites/projects to obtain real data that can verify the Voltage or Electric Field dependence on distance for classic charge distributions

In my most recent post, I tried to investigate the V(r) verses “r” for several charge distributions on conductive paper. The discussion there made me realize that the common conductive paper activity is not suitable for doing that. Nevertheless, I am interested in doing projects where I can find V(r) for some of the basic charge distributions so common to beginning to basic electrostatics like V(r) = kQ/r (point charge), V(r) = (λ/2πε)ln(r2/r1) for ∞ line of charge, or the finite wire, etc. Does anyone know of any real-life experiments where people actually tested out these voltage expressions? I have played around with a capacitor for parallel plates that many science education companies sell. Surely someone must have done this---even if centuries ago---since science always must always be checked. I haven’t found much just doing internet searches but if someone knows of someone who has done real V(r) to test the validity of what we get for these classic charge distributions, point me in that direction. I am willing to get all the materials and do the project. I have worked with a Van De Graaff as a point charge, but there is no easy way to measure “kQ” in that situation for a bunch of reasons I won’t list here.

First of all, if you are going to post a lot more on this forum, you need to look at how your post appears, and maybe think about making it more easily readable. A long, single, continuous paragraph does not make it that easy to read.

Secondly, one often does not measure V directly in situation like this, the same way one doesn't measure the electric field directly. You need a way to use a "test charge" to sample the field of the "source charge".

Thirdly, you can easily measure the Coulomb's force and measure its dependence on distance from the source. This automatically tells you not only the electric field dependence (if you know the quantity of the test charge), but also the potential field, because they are intimately related to one another. You can't have one without the other.

If you look at this http://people.physics.tamu.edu/mcintyre/courses/phys208H/labs/Lab_1.pdf (Problem 2) using the torsion balance, this is the type of experiment that many schools perform at the elementary level.

Please note that if the potential fields for point charges are incorrect, beam physics for particle accelerators would have already gone haywire.

Zz.

 

[Albertgauss]

@anorlunda, the last post was dedicated to using conductive paper to find V(r). That was one subject. Once I realized that you can't use conductive paper projects for V(r) investigations, I felt the post concluded. The next question--which seemed to me like a separate post and new subject---is to find out whether possible projects exist to investigate V(r) for classic charge distributions with other equipment. I also didn't want this idea to get tangled up in the last post.

@ZapperZ, I began reading the "general physics lab experiment". This looks very good and promising. I have been working with some high voltage sources. I do not have a torsion balance, but will now work towards obtaining one. This is very useful.

Also, yes, I know that much physics and technology depends on the derivations of charge distributions as correct. I am not trying to refute or deny their validity. What I am is interested in is projects where I can measure some of these results--E-field, V(r), etc. That is the main goal. I felt that when these ideas were new--maybe 200-250 years ago or so---people must have carried out experiments at that time to test them out. Since, these ideas were eventually validated, there should-have-been/must-be experiments that validated the results of classic charge distributions here. Those experiments is what I was wondering if anyone knew about. If they are not too difficult, I would use them, and that would be useful. We are all taught about classic charge distributions in college through lecture and homework, but there are very few real-life projects to compliment that homework and lecture at the introductory level.