Hello, everybody! I got a homework that confuses me totally. Any help is highly appreciated: Here's the scenario : http://cafeking.2page.de Which frequencies are possible on the assumption that we have a harmonic oscillation? The changing of the charge on the upper plate by q and the momentary elongation x should be considered. I think 'harmonic oscillation' means that we have x=xmax*sin(omega*t) and its derivations as a solution for a differential equation but I can't find an accurate the springs are made of isulating material. I forgot to mention that we have a DC voltage, so the resistance of the capacitor is infinite. In contrast to a AC voltage it has no impendance. As a consequence of that we have a mechanical oscillation - not an electric one. It must look like this: m*s'' + k*s = E*q The electric field strengh E and the carge q must be replced by given parameters whereas the charge on the upper plate is influenced by the coil - especially because of self-induction that hampers the charging on the plate. That's all I can say. My problem is the right equation for the oscillation.