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 P: 94 1. The problem statement, all variables and given/known data I have some working out my lecture gave me to a problem and I don't think I understand part of it. Hoping you could help me. It's using Gauss' Law to find the capacitance of a cylindrical capacitor of length L but this information shouldn't matter for my question. $\lambda=\frac{∂q}{∂l}$ $\oint E \bullet \Delta A = \frac{\sum q}{\epsilon}$ He then jumps to. $E \int \Delta A = \frac{\lambda L}{\epsilon}$ First question, how does he go from the surface integral to the normal integral? Has it got anything to do with removing the dot product? He then changes $E \int \Delta A$ to E(2πrL) I understand this is taking the integral of dA which becomes A, which is the area of a circle, hence 2πr, but how does he then bring the L into play...would this not be the Volume, not the area? Thanks for any help.