1. The problem statement, all variables and given/known data I have a current problem set question about the work per unit area required to separate infinite sheets of charge with equal and opposite charge densities from a separation of d to a separation of 2d. 2. Relevant equations U=(1/8∏)∫E2dV W=∫F*dr E=4∏σ 3. The attempt at a solution I was thinking I could just find the difference in energy stored in the field before and after... so I would integrate E2 over the initial and final volumes, and then the difference must come from work I have put in to the system, which shows up as energy stored in the electric field. If I do this, I get Ui=2∏σ2d and Uf=4∏σ2d And so the work is just 2∏σ2d. But how am I sure that this has units work per area? It seems like work per volume because you have (esu^2)/(cm^3) for the units written out fully. Is there a way to do this by integrating the force (or perhaps the field) rather than finding stored energy changes?