Potential energy of a charge system

1. Oct 2, 2004

agolkar

Hi,
I'm new to the forum and I congratulate with everyone of here for the nice scientific forum you've set up
I apologize in advance for my poor english (especially about scientific terms!), but I hope I can explain my doubt. I'm currently studying for the Electromagnetism exam for my aerospace engineering degree.

After the enunciation of the formula of the potential energy for a charge system (U=1/2 1/(4*pi*epsilon) etc..), in my book I read the following statement about the topic in subject:

"it comes back the simmetric structure regarding the charges, that corresponds the fact that the potential energy of a charge system in every possible configuration is a characteristic of the system in its complex".

The original text in italian is the following (for the curious ones ):

"torna di nuovo la struttura simmetrica rispetto alle cariche, che
corrisponde all'essere l'energia potenziale di un sistema di cariche in ogni
sua possibile configurazione una caratteristica del sistema nel suo insieme

The same assertion about the simmetry regarding the charges is made when introducting the potential energy itself... anyway I cannot understand the point can someone help me, please?

Alessandro

2. Oct 4, 2004

spacetime

electric potential energy

Well, if I understand what you meant, here is the answer.

The author is trying to say that the potential energy is defined only for a system. For example, potential energy of a group of charges, potential energy of the earth-stone system. You can't say potential energy of the electron, rather, potenitial energy of the electron-proton system.

I hope it helps. Tell me if you meant something else.

spacetime
www.geocities.com/physics_all/index.html

3. Oct 4, 2004

agolkar

yes, i think that's the point.
but i cannot understand the relation of it with the simmetry of the formula regarding the charges.... any idea?

thanks again

4. Oct 4, 2004

spacetime

symmetry and Electric potential energy

Agolkar,

If you look at the formula, you observe that by looking at it, you cannot tell whether you have written the potential energy of Particle A or Particle B.
That is, the formula is symmetric with A and B. ( or with all the charges if there are many ).

So, that means, potential energy is not for a particle. Rather, for a system. And the formula tells that too.

spacetime
www.geocities.com/physics_all/index.html

5. Oct 4, 2004

agolkar

thanks!!! i understood!
very clever