1. The problem statement, all variables and given/known data Consider three plane charged sheets, A, B and C. The sheets are parallel with B below A and C below B. On each sheet, there is a surface charge of uniform density: -(4/3) * 10^-5 (Call α) -(7/3) * 10^-5 (Call β) -(3/3) * 10^-5. (Call γ) (The density given includes charge on both sides of the sheet). What is the magnitude of the electrical force on each sheet, in N/m^2 Answers are 3.2pi, 1.4pi and 1.8pi. 2. Relevant equations For an infinite plane, the electrical field strength is: σ/2ε where ε is 8.85 * 10^-12 and σ is charge density. Also, Force = Electric Field * Charge 3. The attempt at a solution dF = EΩdA or dF/dA = EΩ where Ω is the charge density of the plane whose force is being calculated (Can someone verify if this line of reasoning is correct?): The electric field for any patch of area on A should be the average of the electric fields above and below. This comes out to simply be the superposition of the electric fields generated by sheets B & C because the electric field generated by A cancel out on both sides. Therefore, for a small patch of area on A, E: E = (β+γ)/2ε Finally: dF/dA = (β+γ)α/2ε = 8pi For Sheets B & C: dF/dA = (abs(-α+γ))β/2ε = 1.4pi dF/dA = (α+β)γ/2ε = 6.6pi EDIT: So I did a quick test to check something. Apparently if I subtract the two density charge contributions for the electric field for Sheets A & C, I get the right answer but this has only made sense for Sheet B because the electric fields were in opposite directions. For Sheet A, the electric fields are both pointing down towards B & C while for Sheet C, the electric fields are both pointing up towards A & B. Also, I'm curious as to why the answers have pi in it. All my calculations simply didn't require it. Is there another way to do this?