Electrostatics – How Does Positive Charge Spread Out in Conductors?

Question

I know that when there are excess positive charges in a conductor, for example, a metal sphere, the positive charges will spread out over its surface. However, I am confused about how this excess charge spreads out over the surface, if protons cannot move and only electrons can move.
Can someone please inform me on how the excess positive charge spreads out over the surfaces of conductors?

Answer 1

Physically what is happening is this:

• When you touch the positively charged source to the conductor (the metal sphere), electrons leave the conductor through the point of contact.
• This leaves the point of contact on the conductor with a large deficit of electrons, and thus the point has a positive charge density.
• The positive charge density produces an electric field in the conductor, which immediately pulls on remaining electrons in the conductor.
• The electrons remaining spread out until they have eliminated all of the electric fields in the conductor (if there were remaining fields, the electrons would continue to rearrange).
• The electrons will now be 'more spread out' than the protons; the difference between the new electron surface density and the original tells you the distribution of 'excess positive charge' on the surface.

I hope this helps, let me know if you have an application in mind for this; I often times find it helpful in thinking about problems to temporarily ignore the fact that in practice there is only one charge carrier (the electron) and just think about excess positive charge as positively charged particles spreading out.