Every electrical circuit, no matter how complex, is composed of no more than three basic electrical properties; resistance, inductance, and capacitance.

ð resistance is the property of an electrical conductor that opposes the flow of electric current
ð inductance is the property of an electrical conductor which opposes a change in current flow.
ð capacitance is the property of a circuit which opposes a change in voltage.

A capacitor is a passive electronic component that stores energy in the form of an electrostatic field. In its simplest form, a capacitor consists of two conducting plates separated by an insulating material called the dielectric. Capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the plates' separation.
Capacitance also depends on the dielectric constant of the dielectric material separating the plates.

The standard units of Capacitance are listed below

Capacitors are widely used in electronic circuits  Some of the many uses include

ð  to block the flow of direct current while allowing alternating current to pass

ð  to filter out interference, to smooth the output of power supplies

ð  to select particular frequencies from a signal with many frequencies.

Note: Total capacitance in series and in parallel is calculated opposite the the approach used with resistors and inductors.

More on inductors and capacitors later in the course

History: Leyden Jar

The Leyden jar, or Leiden jar, is a device that "stores" static electricity between two electrodes on the inside and outside of a jar. It was invented independently by Ewald Georg von Kleist in 1744 and by Pieter van Musschenbroek in 1745. The latter place of invention, Leiden, Netherlands gave the invention its name. It was the original form of the capacitor. The Leyden jar was used to conduct many early experiments in electricity, and its discovery was of fundamental importance in the study of electricity. Previously, researchers had to resort to insulated conductors of large dimensions to store charge. A typical design consists of a glass jar with conducting metal foil coating the inner (B) and outer surfaces (A). The foil coatings stop short of the mouth of the jar, to prevent the charge from arcing between the foils. A rod electrode projects through the mouth of the jar, electrically connected by some means (usually a chain) to the inner foil, to allow it to be charged. The jar is charged by an electrostatic generator, or other source of electric charge, connected to the inner electrode while the outer foil is grounded. The inner and outer surfaces of the jar store equal but opposite charges.