# Capacitors in series

if there are two capacitors in series and the capacitance of one is known how would i find a value for the other?

nrqed
Homework Helper
Gold Member
dan greig said:
if there are two capacitors in series and the capacitance of one is known how would i find a value for the other?

I am assuming that you know the total capacitance (the capacitance of the two combined), right? Otherwise it's impossible to answer

For two capacitors in series, the total capacitance is given by
${1 \over C_{tot}} = {1 \over C_1} + {1 \over C_2}$, ore, if you prefer $C_{total} = { C_1 C_2 \over C_1 + C_2}$.

You know the total capacitance and C_1 (say). Then you can easily solve for C_2.

Patrick

$${1 \over C_{tot}} = {1 \over C_1} + {1 \over C_2}$$

Well, what is the exact problem? Like he said above, you would need to know the total capacitance, OR the charge and the potential :-) seeing how C=Q/V. When dealing with electricity, capacitors, and resistors... It's best to write down what you are given, have a list of equations next to you and look at the equations to see which ones match up with what you need :-)