1. The problem statement, all variables and given/known data An empty, hollow, spherical conductor with radius R = 20 cm is supported in air. Electrical breakdown occurs when the electric field at the conducting surface exceeds 3.0 × 106 V m−1. What is the maximum charge that can be placed on the sphere? 2. Relevant equations F = k (q/r^2) F = Eq 3. The attempt at a solution Trying to rearrange these to find q, however all I can get is something which cancels out q.