A capacitor is a small charge storage. It consists essentially of two metal surfaces, which are in the component – separated by an insulator – opposite. Capacitors thus represent technical realizations of plate capacitors .

Capacitors are used in electrical circuits for a variety of purposes, such as caching electrical energy, compensating for variations in DC power supplies, filtering frequencies, or affecting the behavior of flip-flops. They are therefore to be found as an elementary component in almost every circuit (**Safety Certified Capacitors**).

## Normal capacitors

Without an applied voltage, the electrons in the capacitor distribute evenly over the metal plates and the connecting lines. If a DC voltage is applied to a capacitor, additional electrons flow to the metal surface connected to the negative pole for a short time, electrons are pulled away from the metal surface connected to the positive pole – the capacitor plates charge themselves electrically.

As the capacitor charges by the external current flow, the voltage between its metal plates increases – the capacitor itself becomes a small voltage source. However, the amount of electrical charge that the capacitor can store when an external voltage is applied is limited.

The ratio of the maximum storable charge Q at an external voltage U is called the capacitance of C the capacitor. The capacity of a capacitor is given in Farad.

## Notation of capacitor values

On each capacitor is printed, which capacity it has and what maximum electrical voltage may be applied to it. The values are given – similar to resistance values – with the following special features:

The capacitance \ Unit [10] {} nFvalue of a capacitor, for example , is often given in plain text in circuit diagrams and on components ( \ Unit [10] {n}the “F” is omitted). In some cases, however, the capacitance value of a capacitor is also 10 ^ 3printed in the power notation ( ). Here, the first two digits indicate the capacitor value (10)and the third digit the power of ten (\ cdot 10 ^ 3) . The value indicated refers to picofarad as the smallest capacity of commercially available capacitors.

Similar to resistors, decimal places are always written after the power factor; a capacity indication of 2n2thus corresponds to a capacity value of \ Unit {nF}. In this way, it is impossible that one could accidentally “read over” a decimal place (**Safety Certified Capacitors**).

According to the capacity specification, a single letter is usually printed directly on capacitors, which indicates the tolerance class of the capacitor. Jmeans, for example, a tolerance of \ pm 5 \%.

Finally, the value of the maximum voltage is still printed, which may be applied to the capacitor (for example, 100for \ Unit [100] {V}).

Illustrative model for capacitors

A simple physical model for describing current, voltage and resistance is to imagine an electric current flow like a water flow. If one sticks to this model, then one can imagine the following model for a condenser: If the lines form a tube system, then one can imagine a condenser as hollow cylinder, in which an exactly fitting, but freely movable piston is; this is therefore on the one hand subdivide the hollow cylinder into two separate half chambers, on the other hand, however, be movable without appreciable friction. At rest, the piston is to be held in a central position by two coil springs attached to the side walls.