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When we calculate the equivalent of the capacitors that are in series and are connected to a battery we assume that the total charge on each capacitor is equal to the next one.

When I look at two capacitors in series the inner plates of the two capacitors are connected by a wire. Why the charge on each of the inner plate doesn't go through the wire in between and make the two plates neutral?

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    \$\begingroup\$ If you connect discharged capacitors in series and connect the series chain across a battery, the charge will be equal on all capacitors as the total charge passing through the circuit will be the same at all points. The voltages across each capacitor will depend of that capacitor's capacitance value as a proportion of the total chain. The charge does pass through the wire and the sets of plates that the wire connects together will be at the same potential \$\endgroup\$ – user1582568 Feb 11 '16 at 17:29
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Pedants like to say the total charge on any capacitor is 0. For every positive charge on one plate, there is a negative charge on the other plate. The same thing holds true for a series combination of capacitors.

Why the charge on each of the inner plate doesn't go through the wire in between and make the two plates neutral?

Because the negative charges on one of those plates are attracted by positive charges on the other plate of the same capacitor.

Say you have two capacitors connected like this:

       C1      C2
A -----||------||------B

You apply 1 V to node A and ground node B.

Now you have positive charge on the first plate of C1, and negative charge on the second plate. Then positive charge on the first plate of C2 and negative charge on the second plate.

The negative charge from C1's right plate doesn't flow to C2 because it's attracted to the positive charge on C1's left plate more strongly than to the positive charge far away on C2's left plate.

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  • \$\begingroup\$ In my comment I was using the term charge as the product of current and time. I think this answer gives a clearer insight as to what is going on at the electron level, nice answer! \$\endgroup\$ – user1582568 Feb 11 '16 at 18:45
  • \$\begingroup\$ @ user1582568 So this sentence in your answer "The charge does pass through the wire and the sets of plates that the wire connects together will be at the same potential " is wrong , right? \$\endgroup\$ – Jack Feb 11 '16 at 19:53
  • \$\begingroup\$ @MaryE, no that's still true. Charge passes through the wire when you are charging the capacitors. That's how you produce a positive charge (deficit of electrons) on one plate of one capacitor and a negative charge (excess of electrons) on the connected plate of the other capacitor. \$\endgroup\$ – The Photon Feb 11 '16 at 21:23

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