What is capacity physically

Physical size
Surname Electrical capacitance
Formula symbol of size C.
Size and
System of units
unit dimension
The electric capacity (Formula symbol C., v. lat. capacitas = Capacity; adjective capacitive) is a physical quantity that defines the ability of a body or certain conductor arrangements to store electrical charge. It is expressed as the ratio of the amount of charge added Q the tension createdU certainly:

Unit: The electrical capacitance is measured in the derived SI unit Farad. A farad (1 F) is the capacity of a capacitor that stores a charge of 1 coulomb (As) when a voltage of 1 volt is applied:

The SI unit Farad, named in honor of the English physicist and chemist Michael Faraday, has now established itself internationally everywhere.

  Obsolete unit: Until the middle of the 20th century, however, the capacity of capacitors was often related to the unit of capacity cm labeled. This is not a length specification, but comes from the fact that the capacitance in the electrostatic CGS system of units, which is hardly used today, is expressed in the length dimension.

The illustration opposite shows a paper capacitor from the company SATOR from 1950 with a capacity according to the imprint of "5000 cm"At a test voltage of"2000 BC". This would be a capacity of approx. 5.6 nF in today's common SI system of units. A capacity of 1 cm in the CGS system of units corresponds to 1.1 pF in the SI system of units, which is the conversion factor 4πε0.

Colloquial name: The term "capacitance" is often synonymous with the electrical component capacitor (English: capacitor) is used. However, this is a colloquial, strictly speaking, incorrect simplification, a case similar to that of electrical resistance. See also: "Capacity normal".

In the case of the accumulator, a term adapted to its properties is used to indicate its "capacity". At first glance, it is a charge amount, usually given in ampere-hours. The operating voltage range of the accumulator is tacitly used as a basis (e.g. 44 Ah / 3V), which means that it is qualitatively a capacity in the conventional sense.

Capacity of certain conductor arrangements

Capacitors as components that are used because of their capacitance are described in detail in the article Capacitor (electrical engineering). The capacity can be precisely determined with a series of -clear-arranged- ladder arrangements. They are often the basis of the components used as capacitors. The following table shows some examples:

Here, where applicable, A. the area of ​​the ladder, d their distance, l their length, R.1 as R.2 their radii. In the schematic representation, the conductors are colored light gray or dark gray and the dielectric is colored blue.

General formula


For any configuration, the following applies to determine the capacity:

In a vacuum this simplifies to:

Category: Electrostatics