# Homework Help: Dipole question

1. Feb 9, 2008

### joker_900

1. The problem statement, all variables and given/known data
OK I really would appreciate some help on this - just a point in the right direction would be great:

The potential due to the electron in a hydrogen atom at distance r from the nucleus is

V = kq[(exp(-2r/a) - 1)/r + (exp(-2r/a)/a]

Where k=1/(4pie0) where e0 is the electric constant

where a is constant and is a measure of the "size" of the atom. Find the magnitude of the electric field at a distance r from the nucleus, r<<a

When an external electric field is applied, show that the atom develops a dipole moment. By considering the force on the nucleus caclulate the size of the dipole moment p. (the answer is 3pie0a^3)

2. Relevant equations

3. The attempt at a solution

I think the first bit is q/4pieoar from taking the negative grad of the potential and then approximating r/a to zero

However this would mean that the force due to the electron at the proton is infinite - help!

Last edited: Feb 9, 2008