Capacitors Homework Help: Solving Ideas for Initial Charge and Kirchoff's Laws

[villampaxo]

any ideas on solving this? (the capacitors are initially charged) I have some ideas but `im not sure which one is correct... I know that Q remains the same between C1 and C2, so that V1C1 + V2C2 = v1'C1 + V2'C2. From there, i don`t know if i can do the same thing for capacitors C2 and C3. I can use Kirchoff for the whole circuit... Is the total charge before and after the switch is closed maintened so that i can use: V1C1 + V2C2 + V3C3= v1'C1 + V2'C2 + V3'C2 ? (Vx' after the switch is closed, Vx before)

 

[villampaxo]

I`d appreciate a quick reply `cause I have exams coming up...

 

[brasilr9]

The net charge of the whole circuit seems to be zero. So I'm not sure that whether you can you use it or not. But I don't have any idea either.

 

[villampaxo]

I think the answer is: that the charge between C1 and C2 is the same before and after the switch is closed, and the total charge of the circuit remains the same so: C1V1 + C2V2= C1V'1+ C2V'2 and also, the total charge of the circuit remains the same so you ve got two equations. I think that kirchhoff can be used too.