Hi! I have trouble with solving this problem and would be really thankful for some help. :) 1. The problem statement, all variables and given/known data Inside a thin, spherical metal-shell with a radius of 50 cm, a smaller homogenous metal-sphere with a radius of 20 cm is placed concentrically. The smal sphere is grounded through a very long cable going through a small hole in the spherical shell. The shell is then given a charge of 2 * 10-8 C. Find the potential of the shell. 2. Relevant equations Electric potential: V = E/Q Gauss law: The integral of the electric fiel over a surface equals the elcosed charge divided with the electric constant. Coloumbs law: F = k * Q1 * Q2 / r2 3. The attempt at a solution The smal metal-sphere is grounded, thus it has zero potential. In order to calculate the electric potential of the outer shell we need to know how much work it takes to move a test charge from the smal sphere to the shell. My plan was to use Gauss law to find the electric field inbetween the sphere and the shell as a function of r, and then integrate it over dr, from r = 0,2m to r = 0,5. However, as there is no enclosed net charge inside the spherical shell, Gauss law yields zero electric field. If I'm not wrong, this means that no work is needed to move a testcharge from the sphere to the shell, and thus the potential of the shell should be zero as well. But my teacher says that this is not the right answer. My other idea was to use Coloumbs law to find the net force on a test charge as a function of r, and then integrate it from r = 0,2m t or = 0,5m. However, finding an expression for the net force exerted by all the charges along the shell was harder then I thought, so I have not yet been able to make it. Do you think I should continue searching for an expression for the net force or is there a more simple way to solve this problem? Is there any special meaning in emphasizing that the grounding-cable is very long (I have not been able to use this information yet)? Thank you for your help!