Capacitance
The ratio of the electric charge stored on a conductor or capacitor plate to the potential difference across it.
Governing formula
C = q / V = ε A / d
SI unit
F (Farads = C/V)
In depth
A capacitor stores energy in its internal electric field established between two separated conductors. Inserting an insulating dielectric material with permittivity ε = ε_r ε₀ increases capacitance by reducing the internal field for a given stored charge.
Examples in the real world
Smoothing capacitors filtering voltage ripple in power supply rectifiers, or capacitive touchscreens detecting fingertip touch through localized capacitance changes.