1. The problem statement, all variables and given/known data I am working on a problem that is similar to this one: https://www.physicsforums.com/showthread.php?t=598914 2. Relevant equations 3. The attempt at a solution When r < a, why doesn't the electric fields generated by the concentric conducting, hollow sphere affect the Gaussian surface at that point?? Why is the electric field at a point in the concentric conducting, hollow sphere zero? After all, it doesn't specify that it is in electrostatic equilibrium. Also, what is the difference between the entire system being in electrostatic equilibrium and just the concentric conducting, hollow sphere being in electrostatic equilibrium? Can an insulator be in electrostatic equilibrium?