Capacitors in the Real World

You may remember Doc Brown in “Back to the Future”, explaining to Marty that the flux capacitor is what makes time travel possible. Well, now is the time to shed some light on this essential electrical component you may find when opening most of your electronic devices.

Principles of capacitors

There are many different types of capacitors, but they basically consist of two plates made of an electrical conductor. These two plates are facing each other and the space in between is filled with an electrical insulator that can be polarized when exposed to a magnetic field. Such insulators – like ceramic, glass, paper or even air – are said to be dielectric.

When the circuit is powered with a continuous source of electrical current, negative charges accumulate on one plate, while positive charges accumulate on the other plate. After a certain amount of time, the plates are fully charged and charges stop flowing through the circuit. However, if the circuit is powered with an alternating source of current, charges keep flowing, establishing a permanent current in the circuit. To control the characteristics of the capacitor, one can modify the distance between the plates, alter their dimensions or change the nature of the dielectric medium.

Real world capacitors

Intuitively, we can see that capacitors have the interesting property of behaving differently depending on the nature of the power source. When the applied voltage is continuous, then the capacitor behaves as a turned-off switch and the continuous component of the current is then removed. In the other hand, when the power source consists of a time-varying voltage, the capacitor can exhibit interesting properties and act as a power source stabilizer. As a matter of fact, capacitors have important applications in the field of short-term energy storage. For instance, they are very helpful to maintain the level of the power supply while batteries are being changed.

On the contrary, they are also used for their capability of delivering high magnitude spikes, very useful to start motors by initiating the engine movement. The nature of these spikes are also very much appreciated in the field of electromagnetic weaponry, such as the production of electromagnetic pulses or the construction of high-intensity lasers.

Some other applications involve interesting properties that arise at some specific frequencies: this is the resonance phenomenon. This is fundamental in the field of radio telecommunication, where it is necessary to select and amplify the information contained within a specific frequency range.

On another note, one can also use a specific phosphorescent dielectric medium to produce light, which is the source of back lighting adopted in certain laptops. Capacitors have also proven to be a very efficient way of producing light for largere electroluminescent panels.

As we have seen, capacitors are literally everywhere around us. From coffee machines to cell phones, they serve the purpose of protecting sensitive circuit parts from unstable power surges or unexpected power outages. Their very simple nature makes them a very interesting passive electrical component. Industries have been making an extensive use of capacitors, and this isn’t likely to stop anytime soon.