Capacitance

A capacitor stores charge on two plates. The plates carry equal and opposite charges: if one plate has charge $$$+Q$$$ , the other has charge $$$-Q$$$ . There is a potential difference $$$V$$$ between the plates.

Capacitance measures how much charge is stored per unit potential difference across the capacitor:

C = \frac{Q}{V}

Here, $$$C$$$ is the capacitance, $$$Q$$$ is the magnitude of the charge on either plate, and $$$V$$$ is the potential difference between the plates. For the same potential difference, a capacitor with a greater capacitance stores more charge on each plate.

For a capacitor whose capacitance is constant, rearranging the relationship gives:

Q = CV

The stored charge is therefore directly proportional to the potential difference: doubling $$$V$$$ doubles $$$Q$$$ .

The SI unit of capacitance is the farad ( $\mathrm{F}$ ). One farad is one coulomb per volt: $1,\mathrm{F} = 1,\mathrm{C},\mathrm{V}^{-1}$ .