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Capacitors in DC Circuits

Capacitors do not play an important role in DC circuits because it is impossible for a steady current to flow across a capacitor. If an uncharged capacitor $C$ is connected across the terminals of a battery of voltage $V$ then a transient current flows as the capacitor plates charge up. However, the current stops flowing as soon as the charge $Q$ on the positive plate reaches the value $Q=C\,V$. At this point, the electric field between the plates cancels the effect of the electric field generated by the battery, and there is no further movement of charge. Thus, if a capacitor is placed in a DC circuit then, as soon as its plates have charged up, the capacitor effectively behaves like a break in the circuit.

Richard Fitzpatrick 2007-07-14