http://www.edexcel.com/migrationdoc...um 2000/june2010-qp/6PH04_01_que_20100618.pdf Hi, I'm preparing for my exams, but I can't understand something about the question Q16 (part b i). The answer is: Capacitor stores charge/charges up (1) (If voltage is constant) capacitor doesn’t discharge (1) But, where is constant voltage? Is it across a capacitor or in a power supply? As far as I know, voltage across the capacitor matches the voltage of power supply, and because we basically have no resistance the time lag between increase/decrease in voltage of power supply and change in voltage across the capacitor is small. So, if the voltage of the power supply changes, and the voltage across the capacitor changes (matches with the change in power supply) as well, where does constant voltage come from? Thanks.