1. The problem statement, all variables and given/known data I'm trying to calculate the electric field through two oppositely charged plates with the same magnitude: http://imgur.com/uXCQqtW [Broken] 2. Relevant equations Flux = ∫E⋅dA = Qenclosed/ε0 3. The attempt at a solution I understand how the electric field is calculated using S1 and S4, but I have one question: Why did the Gaussian surface have to contain a part of the plates? I ask this because if the surface was chosen to be between the plates, but not containing any parts of the plates, the electric field would be zero, since Qenclosed is zero and the area, A, as well as ε are both constants. But, the electric field is definitely not zero between the plates.