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The situation I'm referring can be seen in the following link (ignore the numerical value, let's just call it $V$)

https://www.google.com/imgres?imgurl=https%3A%2F%2Fwww.physicsforums.com%2Fattachments%2F1-png.78645%2F&imgrefurl=https%3A%2F%2Fwww.physicsforums.com%2Fthreads%2Fthree-plate-capacitor-and-charge-distribution.796096%2F&tbnid=l_UMEXNCfMKVZM&vet=12ahUKEwjxg-n42brxAhXRAewKHaDoDLcQMygCegUIARC8AQ..i&docid=hQxm8teIbSNYVM&w=209&h=173&q=three%20plates%20capacitor%20charge%20distribution&ved=2ahUKEwjxg-n42brxAhXRAewKHaDoDLcQMygCegUIARC8AQ

I want to find the charge, $Q$, on plate B. Im pretty sure I can just view it as two parallel capacitors and this results in $Q=(C_1+C_2)V$, where $C_i$ can be calculated with the usual formula for parallel capacitors (just suppose that we know the area and the two distances $d_i$ between $AB$ and $BC$). The problem arises when I try to intuitively picture this as charges moving from one plate to another, by means of the generator. The generator will move a charge equal to $Q_1=C_1V$ from plate $A$ to plate $B$ and a charge $Q_2=C_2V$ from plate $C$ to plate $A$. This will result in plate B having a negative charge equal to $-Q_2-Q_1$ and plates $A$ and $C$ having, respectively, charges $Q_1$ and $Q_2$. This just does not feel right to me, because capacitors usually have net charge $=0$, but if I consider capacitor $AB$ the net charge is $-Q_2$ and similarly for capacitor $BC$. Where is the flaw in my reasoning? Thanks a lot

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Imagine Three boxes, enclosing respectively $A$, $B$ and $C$ (each box enclosing only one plate and having a top and a bottom side of area S).

Applying Gauss’s theorem on the Box $Ba$ surrounding $A$

$Eab.S = Qa$

Ditto for $B$ and $C$:

$ (Eab + Ebc).S = Qb$

And:

$Ebc.S = Qc$

Since $Eab = Ebc = V$,

$Qa = Qb = (1/2) Qbc$

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