Capacitor

A Capacitor is one of the fundamental four passive electronic components, together with Resistors, Inductors and Memristors.

It's widely used in Analog computers as the key element in the Integrator, Track & Store Circuit and as stabilizer in uncommitted or Open Amplifiers.

It is capable of storing a certain amount of electrical charge (measured in Coulombs) depending on a propriety called Capacitance. The larger the capacitance, the larger the amount of charge stored and longer the time needed to charge.

An analogy useful to understand capacitor behaviour is by comparing it to a bucket. The larger in volume the bucket, the longer the time to fill it by a pipe carrying so many liters per second. The amount of water is definite and proportional to the volume of the bucket itself. The bucket can also be emptied instantly, akin to how capacitors can discharge instantly by being short-circuited.

Basics of Capacitors

A capacitor in its most basic form is created by putting two metal plates, called armatures or simply 'plates' facing each other.

Usage in Analog Computers

First and foremost, Capacitors can be defined as the 'heart' of the Integrator. By taking a simple Summer and taking out its feedback resistor, which has a linear relationship betwixt current and voltage (I = V/R, Ohm's Law), and substituting it with a capacitor an integrator is obtained. The relationship betwixt current and voltage in a capacitor is, in fact, I = C*(dV/dt) and shows a time-dependent behaviour which leads, eventually, to the normal Integrator transfer function. For more details, see the related Integrator page.

Second, capacitors are used in Track & Store circuits.