I have a circuit with capacitors on it:

circuit figure 1

I am trying to figure out the charge on each capacitor.

The following is given:


i know that parallel capacitors follow the equation


and that capacitors in series behave according to this equation: series

I dont know how to use that knowledge to find out the charge of the capacitors. I also dont know how to apply this to find the voltage across all the capacitors and the total voltage.

This is from a homework question but i want to find out the general concepts of calculating voltages and charges on any circuits.

Any help will be greatly appreciated.

  • $\begingroup$ Just apply Kirchoff's Loop Law and conservation of charge. $\endgroup$ – evil999man May 14 '14 at 8:43

If two capacitors are in series the charge on them must be the same. This is because there is no source or sink for charge in between the two capacitors:


That means $Q_1 = Q_2$. You know $Q_2$ so you now know $Q_1$ and you can calculate the voltages $V_1$ and $V_2$ and the total voltage across both, $V_{12}$.

Because $C_3$ is parallel with $C_1 + C_2$ you know $V_3 = V_1 + V_2$ and from this you can calculate $Q_3$. Finally, if you calculate the combined capacitance of $C_1$, $C_2$ and $C_3$ and you know the voltage across this combined capacitor $V_{123}$ you can calculate a combined charge $Q_{123}$, and because $C_4$ in series $Q_4 = Q_{123}$.


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