Capacitors are devices that can store charge. Generally, conventional capacitors consist of two conducting objects placed near each other but not in direct contact with one another; accordingly, a potential difference across the conductors can be established, and the capacitor can thereby be said to be storing energy electrostatically in the corresponding electric field. Capacitors are widely used in electronic circuits. For example, they can be used to store energy for later use, as in a camera flash, or alternatively as energy backup in case of a power failure. Capacitors can also be used to: block surges of power to protect circuits; form parts of a radio; and serve as memory for binary code in random access memory (RAM). The energy stored in a conventional capacitor is a function of the potential difference across its conductors as well as its capacitance, which is generally an inherent property of the capacitor. Capacitance is typically measured in farads, which is equal to coulombs per volt.
Supercapacitors (also known as ultracapacitors, electrochemical capacitors, or double-layer capacitors) represent relatively recent developments in the field of capacitors. Supercapacitors utilize similar principles as conventional capacitors insofar as they are configured to store energy in electrostatic fields; however, they implement different architectures and thereby achieve much higher capacitances. For example, whereas conventional capacitors typically have capacitances in the range of microfarads, supercapacitors can have capacitances on the order of hundreds of farads.