Farads

The farad is the SI unit of electrical capacitance. It is defined as the capacitance of a capacitor that stores one coulomb of charge for every volt of potential difference across its plates. In symbols, one farad equals one coulomb per volt (F = C/V).

Named after Michael Faraday, the unit was formalized in the modern SI system to quantify a device’s ability to store charge.

Because a farad is a large unit, practical capacitors are commonly specified in smaller submultiples such as microfarads (µF), nanofarads (nF), and picofarads (pF). In base units, the farad can be expressed as F = A^2 s^4 /(kg m^2).

Capacitance determines energy storage: E = 1/2 C V^2. Common uses include energy storage in power supplies, filtering, decoupling, coupling signals, timers, and tuned circuits.

Example: a 1 µF capacitor at 5 V stores about 12.5 microjoules of energy (E = 0.5 × 1e-6 F × 5^2). In larger applications, devices such as supercapacitors can reach several farads, enabling rapid energy storage for power backup and other high-demand roles.