Energy storage, provision of flexible filter options, power conditioning and coupling are some applications of a capacitor. Together with resistors, capacitors are used as main elements of frequency selective filters.
A capacitor can be used to store electric energy when connected to its charging circuit. When disconnected from the charging circuit, it can dispel the stored energy and act like a temporary battery.
A reservoir capacitor is used in power supplies in smoothing the output of a full or half-wave rectifier. Since a capacitor can pass AC signals to blocking DC, it can be used to split up AC and DC components of a signal. To allowing coupling, the value of the capacitor need not be accurate, but it should have a high value as its reactance power.