Question

A an atom with radius r = 5.29*10^-11 m and a polarizability P = .667 is is located a distance d = 3*10^-3 m from a point like charge q = 15*10^-6 C

How large would the point like charge have to be to ionize the atom?

Answer 1

An atom can ionize when placed in an electric field.

Assuming that the point charge is in the shape of a sphere. This point charge (given as q= 15* 10^-6 C) provides the electric field, E, necessary to ionize/polarize the atom.

Now if we look at the how E varies for a uniformly charged sphere, we obtain that for a point outside the sphere, the electric field is identical to the that of a point charge of the same charge, placed at the center of the sphere.

Thus, the size of the point charge has no effect on the electric field provided by it and consequently no effect on the ionization of the atom.