%path = "physics/electricity/capacitor" %kind = kinda["fragments"] %level = 12 In a capacitor negative charge \(Q\) (unit A(mpere)s=C(oulomb)) is brought close to positive charge via a voltage \(U\) (unit V(olt)). Because of the mutual attraction of the opposite charge the capacitor discharges only slowly. The capacity \(C\) (unit F(arad)) says how much charge per voltage can be loaded: \(C=\frac{Q}{U}\) oder \(Q=CU\). If we unload a capacitor via a resistor \(R\), we have \(-RI=\frac{Q}{C}\), i.e.. -voltage drop at resistor (\(U=RI\)) is equal to voltage drop at capacitor. Because \(I=\frac{dQ}{dt}\) we get a differential equation \(\frac{dQ}{dt}=-\frac{Q}{CR}\), which can be solved via separation of variables ({{!util.a('r.f')}}).