Why do capacitors 'in series' each carry the same charge?

[jrdelacruz]

Homework Statement

Exactly from my homework:
"It is assumed that for capacitors 'in series' that each capacitor carries the same charge Q. Give a physical argument for this. Why does this make sense?"

Homework Equations

The Attempt at a Solution

I've tried searching for the answer, and none of it is making sense to me, perhaps someone can explain it in a simpler way? This is what I have come up with so far, please help me finish/correct it:

"Let us assume that there are 2 capacitors connected in series by a battery, capacitor 1 consists of plates A and B of size X and capacitor 2 consists of plates C and D of size Y. The plates are lined up in series alphabetically. Going to plate A is a positive charge Q. This means the charge –Q will be on D."

 

[Redbelly98]

Welcome to Physics Forums.

You have a conductor comprising the connection between the capacitors, and one plate from each capacitor. This conductor is insulated from anything else. What must the net (i.e. total) charge on this conductor be?

 

[vela]

You're just restating what they asked you to explain. You haven't said why -Q has to be on plate D.

When you place charge +Q on plate A, where does the charge -Q on plate B come from?

 

[jrdelacruz]

What must the net (i.e. total) charge on this conductor be?

The net charge on the conductor should be 0. But how does that relate to the problem?

When you place charge +Q on plate A, where does the charge -Q on plate B come from?

The charge -Q on plate B comes from the charge +Q of plate A. All of the electrons from the conductor (plate B and C) will move to plate B because of the +Q of plate A right?

 

[vela]

Now put it all together. You said the net charge on plates B and C is zero and that the charge of +Q on plate A will attract a charge -Q onto plate B. Charge is conserved, so how much charge must be on plate C?

 

[jrdelacruz]

So that means there must be a charge Q on plate C! So, now I know each capacitor has a charge of Q, is it safe to say that each plate has a charge of magnitude Q?

 

[Redbelly98]

So that means there must be a charge Q on plate C! So, now I know each capacitor has a charge of Q, is it safe to say that each plate has a charge of magnitude Q?

Yes, correct.