# Electric Charges

1. Jan 22, 2007

### Soaring Crane

Why do electric charges of opposite sign attract each other but charges of the same sign repel each other?

2. Jan 22, 2007

### ranger

Well there is something called the electric field. By convention, the electric field lines radiate from the positive particle and moves to the negative particle. With that said, once a electron in next to a proton, the field lines will move from positive(proton) to the negative(electron) and act like an attractive force. Likewise, if two protons are next to each other, there is no reason for the field lines to move from + to +, so instead they repel each other.

Note these field lines are abstract and are just used to visualize the electric field.

3. Jan 22, 2007

### ranger

Here is a simulator that shows how the field lines are affected by different particles (electron and proton). It is very useful, you can even drop a test charge (+ or -) into the electric field and trace is path to see which particle it will move towards.

http://www.vias.org/simulations/simusoft_efield.html

Last edited: Jan 22, 2007
4. Jan 22, 2007

### Claude Bile

I don't think anyone has come up with a suitable explanation as to why this is, (if anyone has I would love to hear it) it's one of those fundamental things that cannot be explained using a 'more fundamental' concept.

Claude.

5. Jan 22, 2007

### americanforest

I was thinking about just the same question today. Atoms need to stay neutral, so that's why they attract opposite charges, but why do they repel positive charges. It doesn't help them gain neutrality, does it?

6. Jan 22, 2007

### ranger

I'm confused by what you are trying to say.

7. Jan 22, 2007

### americanforest

Atoms want a full valence shell. To achieve this they attract positive or negative charge as necessary. This makes sense and gives an explanation of why opposite charges attract. Now I'm trying to think of an explanation of why charges of the same sign repel. It doesn't bring the atom any closer to a full valence shell, so that is not a valid explanation.

8. Jan 22, 2007

### ranger

Ah, okay. Well atoms dont "attract" charges because atoms are neutral. It is not necessary to have a full shell either, the shell can also be empty. Example, sodium which has 2/8/1 electron configuration, will easily give up an electron and become 2/8 sodium ion. Also only electrons are exchanged among atoms, they dont attract positive charges (protons). Can you imagine electrons and protons "orbiting" the nucleus of the atom?

As for the explanation of attraction and repulsion among electric charges, the best explanation that I know of is by using the electric fields.

Last edited: Jan 22, 2007