Right. Suppose you have a metal container. In a static (stationary) case, with various electrical fields outside it, the electrons would run around until the electric fields from the outside, and the ones due to the electrons in the metal, balance out. The same thing happens to the molecules in a glass of water, affected by gravity. They slosh around untill the forces are balanced, then it stops moving and the surface becomes flat. It happens that, on the inside of the metal container, the electric potential (voltage) is now the same everywhere, otherwise, the electrons would continue to move around. Eventually everything would come to rest. Your semiconductor carbon container would do the same, but--- If the fields outside are changing, the electrons in the container material have to constantly run around to catch up. This is frequency dependent - it gets harder as the frequency goes up. You obviously want as low a resistance as possible - pure silver would be best, and the high-resistance carbon will only work for static (stationary fields) or slowly-changing low-frequency outside fields. Not good for protecting your stuff from radio waves if any kind.