farad

The farad (symbol F) is the SI unit of capacitance, a measure of how much electric charge a device can store per unit voltage. It is named after the English physicist Michael Faraday, in recognition of his work on electrostatics and electromagnetism. By definition, a capacitor has a capacitance of 1 farad if it stores 1 coulomb of charge when the voltage across its terminals is 1 volt, so that Q = C·V with Q = 1 C and V = 1 V.

In terms of base units, the farad is defined as 1 F = 1 C/V = 1 A·s/V. Since a volt is itself defined from base units, the farad is a derived SI unit and can be expressed as 1 F = s^4 A^2 / (kg·m^2).

Submultiples and common values include the millifarad (mF = 10^-3 F), microfarad (µF = 10^-6 F), nanofarad (nF = 10^-9 F), and picofarad (pF = 10^-12 F). In practice, most electronic capacitors are in the range of µF to nF, with smaller pF values used in high-frequency circuits and larger mF or F values in energy storage applications such as supercapacitors.

Applications and formulas: capacitance reflects a component’s ability to store charge, and energy stored is E = 1/2 C V^2. Thus a 1 F capacitor charged to 1 V stores 0.5 joules. The farad is fundamental in electronics, influencing circuit behavior in filters, timing, power supply decoupling, and signal coupling.