A very weird capacitor association

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The discussion focuses on calculating the equivalent capacitance of two capacitor associations, labeled a) and b). The initial calculations included multiple capacitances, but feedback indicated that only specific capacitances were considered relevant. The confusion arises from understanding why certain capacitances were ignored, highlighting the importance of the charge distribution and potential difference defined by the connected source. The relationship between surface charge density, electric field strength, and vacuum permittivity is emphasized as crucial for determining the net charge on the plates. Ultimately, the conversation seeks clarity on the methodology used in the capacitance calculations.
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In the capacitor association a) and b), calculate the equivalent capacitance
Given: area = A, vacuum permissivity = E, distance between each plate = d[PLAIN]http://img714.imageshack.us/img714/7073/semttulojznw.jpg In the first I've calculated the capacitance of AB, AC, AD, BE, CE, DE and added them. In the second the capacitance EF, EH, FG, FI, FH, HI and added

However the feedback only added AB and DE (in the first) and EF, FG, GH, HI in the second. Why have some capacitances been ignored?
 
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You can start from the definition of the capacitance: C=Q/U, charge on one plate divided by the potential difference between the plates. The potential difference is defined by the source, connected between points + and -. You need to determine the net charge on the plates connected together. The charge is distributed on the surfaces of the metal plates, and the surface charge density σ is equal to the electric field strength multiplied by the permittivity of vacuum: σ=ε0E where E=U/d.

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