Hello, I'm studying capacitors in my freshman physics class and I'm not quite following my book here. My book states that we can calculate the potential energy U stored within a capacitor by calculating the work done to charge it. Let q and v be the charge and the potential difference, respectively, at an intermediate stage during charging. To transfer an additional element of charge dq, the work dW required is given by dW = v dq I'm not quite seeing how they got the above equation though. I'm aware that the work from point a to b divided by a unit charge gives the difference in voltage, but I'm not seeing how they can get the above equation from that and I'm clueless as to how else they'd get it from. Any clarification would be much appreciated.