Self-capacitance
In electrical circuits, the term capacitance is usually a shorthand for the mutual capacitance between two adjacent conductors, such as the two plates of a capacitor. However, for an isolated conductor there also exists a property called self-capacitance, which is the amount of electrical charge that must be added to an isolated conductor to raise its electrical potential by one unit (i.e. one volt, in most measurement systems). The reference point for this potential is a theoretical hollow conducting sphere, of infinite radius, centered on the conductor. Using this method, the self-capacitance of a conducting sphere of radius R is given by:
Example values of self-capacitance are:
- for the top "plate" of a van de Graaff generator, typically a sphere 20 cm in radius: 20 pF
- the planet Earth: about 710 µF
The capacitative component of a coil, which reduces its impedance at high frequencies and can lead to resonance and self-oscillation, is also called self-capacitance as well as stray or parasitic capacitance.
Read more about this topic: Capacitance