1. The problem statement, all variables and given/known data There is a sphere of uniform charge, with a hollow sphere inside it, centered on the x-axis. Show that the electric field in the cavity is constant, and find its value. 2. Relevant equations 3. The attempt at a solution The problem suggested to use superposition. So I thought of breaking it into two parts. The first one being the biggest sphere around the cavity, and the second being everything else. The first part by symmetry cancels out, then we have the second part. There I am stuck. Any help please?