What Is a Spherical Capacitor?

spherical-capacitor Credit: Adastra/Taxi/Getty Images

A spherical capacitor consists of two hollow, concentric spheres of oppositely charged electrodes with an insulator in between them. Physicists consider Earth to be a huge spherical capacitor surrounded by the ionosphere, with a charged atmosphere that discharges electricity to the surface of the planet in the form of lightning.

Using the planet as an example, the inner sphere is negatively charged during fair weather while the air between the ground and the ionosphere is positively charged. The electrical field in between the spheres is produced closer to the surface of the inner sphere. The planetary insulator is the air. Lightning is one method by which the air's insulating capabilities are overcome to stabilize the atmosphere. Scientists calculate, under normal conditions, that the Earth's total charge would dissipate in 10 minutes if not for the atmospheric processes that produce currents in the air.

The amount of capacitance, or energy that can be stored, in a spherical capacitor depends upon the radius of each sphere in the capacitor as the greater the distance between the two spheres, the greater energy each can store. The medium, or insulator, in between the spheres also affects how electricity flows between the spheres and thus affects capacitance as well.