Capacitance

Capacitance is the ability of a body to store an electrical charge. Any body or structure that is capable of being charged, either with static electricity or by an electric current, exhibits capacitance. A common form of energy storage device is a parallel-plate capacitor. In a parallel plate capacitor, capacitance is directly proportional to the surface area of the conductor plates and inversely proportional to the separation distance between the plates. If the charges on the plates are +q and −q, and V gives the voltage between the plates, then the capacitance C is given by

The capacitance is a function only of the physical dimensions (geometry) of the conductors and the permittivity of the dielectric. It is independent of the potential difference between the conductors and the total charge on them.

The SI unit of capacitance is the farad (named after the English physicist Michael Faraday); a 1 farad capacitor when charged with 1 coulomb of electrical charge will have a potential difference of 1 volt between its plates. Historically, a farad was regarded as an inconveniently large unit, both electrically and physically. Its subdivisions were invariably used, namely the microfarad, nanofarad and picofarad. More recently, technology has advanced such that capacitors of 1 farad and greater can be constructed in a structure little larger than a coin battery (so-called 'supercapacitors'). Such capacitors are principally used for energy storage replacing more traditional batteries.

The energy (measured in joules) stored in a capacitor is equal to the work done to charge it. Consider a capacitor of capacitance C, holding a charge +q on one plate and −q on the other. Moving a small element of charge dq from one plate to the other against the potential difference V = q/C requires the work dW:

where W is the work measured in joules, q is the charge measured in coulombs and C is the capacitance, measured in farads.

The energy stored in a capacitor is found by integrating this equation. Starting with an uncharged capacitance (q = 0) and moving charge from one plate to the other until the plates have charge +Q and −Q requires the work W:

Read more about Capacitance:  Capacitors, Capacitance Matrix, Self-capacitance, Elastance, Stray Capacitance, Capacitance of Simple Systems

Other articles related to "capacitance, capacitances":

Capacitive Sensing - Design - Projected Capacitance
... There are two types of PCT self capacitance, and mutual capacitance ... of the sensor changes the local electric field which reduces the mutual capacitance ... The capacitance change at every individual point on the grid can be measured to accurately determine the touch location by measuring the voltage in the other axis ...
Lipid Bilayer Characterization - Electrical
... to perform AC electrical characterization to extract information about the capacitance and complex impedance of a bilayer ... Because capacitance is inversely proportional to thickness and bilayers are very thin they typically have a very large capacitance, on the order of 2µF/cm2 ... Capacitance measurements are particularly useful when dealing with black lipid membranes, as they can be used to determine when the solvent/lipid plug thins down to a ...
Scanning Capacitance Microscopy
... Scanning capacitance microscopy (SCM) is a variety of scanning probe microscopy in which a narrow probe electrode is held just above the surface of a sample and scanned across the ... surface of the sample using information obtained from the change in electrostatic capacitance between the surface and the probe ... SCM was initially devised as a quality control tool for the RCA/CED (Capacitance Electronic Disc), a video disk technology that was a predecessor of the DVD ...
Capacitance Meter - Simple and Non-bridge Meters
... Many DVMs (digital volt meters) have a capacitance-measuring function ... voltage the slower the rate of rise, the larger the capacitance ... DVMs can usually measure capacitances from nanofarads to a few hundred microfarads, but wider ranges are not unusual ...
Capacitance of Simple Systems
... Calculating the capacitance of a system amounts to solving the Laplace equation ∇2φ=0 with a constant potential φ on the surface of the conductors ... Capacitance of simple systems Type Capacitance Comment Parallel-plate capacitor ε Permittivity Coaxial cable ε Permittivity Pair of parallel wires Wire parallel to wall a Wire radius d ...