1. The problem statement, all variables and given/known data We have a crude model for the polarization of a hydrogen atom, by approximating its 1s orbital with a uniformly charged ball of radius a. What is the (negative) charge density of the electron cloud? What is the electric field inside the cloud, at the point with radius vector r (drawn from the center of the cloud)? 2. Relevant equations Equation for charge density Gauss' Law 3. The attempt at a solution I was confused as to how to go about setting up the problem. For the charge density I was thinking simply dividing the total charge by the volume of the charged ball. For finding the electric field inside the cloud, I was considering using Gauss' law when a < r.