# Capacitance **The ability of an electrical conductor or a set of conductors to store [[Electric Charge|charge]] and thus oppose a change in voltage across it. ** > [!infobox] Capacitance > > | | | > |:------------------------------- | ---:| > | ***Symbol*** | $C$ | > | ***SI unit*** | farad, $\text{F}$ | > | ***SI base units*** | $\text{A}^{2}\;\text{s}^{4}\;\text{kg}^{-1}\;\text{m}^{-2}$ | There are two forms of capacitance, *self* and *mutual capacitance*. In general, "capacitance" refers to mutual capacitance. Capacitance is dependent on the *geometry* of the conductors, specifically the distance between them and the surface areas opposing each other, and the *permittivity* of any material between the conductors. ## Self capacitance > [!NOTE] Self capacitance > *Self capacitance* is the amount of electric charge required to raise the electric potential of an isolated conductor by one unit, typically volts. > $C=\frac{q}{V}$ > - $C$ - *self capacitance* of the conductor, $\text{F}$ > - $q$ - amount of added *[[electric charge]]*, $\text{C}$ > - $V$ - the *electric potential* generated in the conductor, $\text{V}$ Any object that is capable of being electrically charged has *self capacitance*. In self capacitance, the potential difference is measured *relative* to a reference, typically ground. ## Mutual capacitance > [!NOTE] Mutual capacitance > *Mutual capacitance* is the ratio of the magnitude of electric charge held on either conductor to the potential difference between the conductors in a system of mutual capacitance. A example of a system of mutual capacitance is found in parallel-plate [[Capacitor|capacitors]]. > If the charges held on the plates are $+q$ and $-q$ and the voltage between them is $V$, then the capacitance is also given by > $C=\frac{q}{V}$