Hey guys Im doing a small signals and noise course this year as part of physics and im trying to wrap my head around a few things, namely in what way to actually use Fourier transforms. Say i have (sorry about the lack of pictorial aids but its pretty easy to picture) a voltage/current source which is connected in series to a resistor then a capacitor. I then take two leads, one on either end of the cap so it becomes a voltage divider. Say for example we had to find the norton/thevenin equivalent of this circuit. Now i know in DC you'd use ohms law to get current through the circuit, then voltage over the resistor in the place of a cap and then get the resistance and you're done. What i don't get with AC is when and where to apply the fourier transform? Do i apply it to the voltage function and the impedance of the cap and then fiddle in fourier space and come back? Cheers -Graeme EDIT: Just realised (duh) that cap impedance is a function of f already, i need not apply the transform then?