1. The problem statement, all variables and given/known data A grounded spherical shell has inner radius of 1m. and outer radius of 2m. Q1=1 Coul. is located at x=0.5m and Q2=-2 Coul. is located at x=4m, respectively. 2. Relevant equations Find the charge system to find the potential outside the shell. Find the charge system to find the potential inside the shell. Obtain the expression for potential along the x axis. 3. The attempt at a solution I found the image charge of Q1 outside the shell and Q2 inside the shell but i'm not sure about which surface i'm supposed to find the image charge of Q2 according to. Is it outer surface or inner one? And what is the difference between the charge system that we're using to obtain the potential of outside the shell and the charges we're using to find the potential inside the shell. Do they differ?