Capacitors

Capacitors are energy storage devices. Compared with an inductor, a capacitor can store energy without a continuous current flow. This is why we need to discharge a capacitor after a high voltage is removed from it, otherwise, the energy can be stored in a capacitor for a while.  

The simplest form of a capacitor is two conductors separated by a dielectric material such as air. You might not realise it, but if you see a power transmission line over the earth, each cable forms a capacitance with the earth. When an aeroplane flies over, there's capacitance between the aircraft and the earth. Just look around your factory building, beams, pipes, and conduits all have capacitance between them. That's why parasitic capacitance is everywhere in the real world.  

As a main energy storage device, capacitors need to be made with a high dielectric material so that they can store more energy. A discussion on the subject of capacitors could easily become a book or a dictionary.  

To start with, there are different types of capacitors such as electrolytic, NiMg, ceramic capacitors, and so on. Then, within the same type, there are different dielectric materials. There are also different classes. As for physical construction, there are two-terminal and three-terminal capacitor types. There's also an X2Y type capacitor which essentially is a pair of Y-capacitors packaged in one.  

The impedance of an ideal capacitor is given by:

where:

• $X_C$= Capacitive reactance (in ohms, Ω)

• $f$= Frequency (in hertz, Hz)

• $C$= Capacitance (in farads, F)