Objective: Investigation of how the voltage across a capacitor changes over time when the capacitor is charging or discharging
In a DC circuit, current only flows through a capacitor at the point in time when the power is turned on or off. The current causes the capacitor to charge up until the voltage across it is equal to the voltage applied. When the power is switched off, the capacitor will discharge till the voltage across it drops to zero. A plot of the capacitor voltage against time can be shown as an exponential curve, i.e. the voltage drops by half in the space of a fixed period T1/2 called the half-life. The same period elapses when the voltage drops from a half to a quarter and from a quarter to an eighth. The half-life period is proportional to the capacitance and the resistance through which the capacitor discharges.