Home Chapter 4 Capacitors: a quick storehouse of electrons
Capacitors: a quick storehouse of electrons
Chapter 4

"The function of Art is to disturb. Science reassures." ~George Braque

Question: Are there electronic devices that allow you to hold electrons in an electronic container as a kind of reserve, but unlike a battery, to make the electrons available instantly?

Capacitors are devices designed to store electrons on two or more parallel plates (image directly below) and they are used in almost all electronic circuits. The parallel plates are close together and are separated by a dielectric insulator. The insulator increases the amount of charge stored on the plates by keeping sparks from jumping the gap and discharging the capacitor. The dielectric can be air as below or it can be another dialectric material such as myler, ceramic, glass or tantalum. Each dialectric material or insulator allows the capacitor to exhibit different characteristics when voltages and frequencies are applied.


Interior of a capacitor with metal plates storing electrons on the surface.


A capacitor is similar to a battery in that it can store an electric charge, however unlike a battery, capacitors can discharge their electrons instantly and therefore they must be handled with care. (Especially very large ones)

In a simple capacitor with two plates, the negative terminal of a battery (or some other voltage source) is connected to one plate and pushes electrons onto the plate, while the other plate, connected to the positive terminal of the battery, pulls electrons from the plate. Generally, capacitors have many parallel plates that determine the amount of capacitance they have and kind of insulating dielectric that is used. The dielectric thickness and surface area that the electrons can rest on also determines an increase or decrease in capacitance.


A common ceramic capacitor. The 104 on the case is a common way of identifying the capacitor. The value is 10 with four zeros added, or 100000. If you count over six places from the decimal point, right to
left, you end up with .1 µF.or .1 microfarad. This can also be written as 100 pF which are functionally the same. 


 Various schematic symbols for capacitors: fixed with no polarity, polarized with definite polarity and variable capacitors.


The farad (F) is the unit of capacitance, but because this unit consists of far too many electrons for most electronic circuits, capacitance is generally measured in microfarads (µF), which is one-millionth of a farad, or Pico farads (pF), which is one-millionth of a microfarad.

Capacitors come in a variety of shapes and sizes, as well as a variety of dielectric materials as mentioned above such as ceramic, polypropylene, electrolytic, polyester (Mylar), polystyrene, polycarbonate, aluminum foil, mica, Teflon, and tantalum.

All these materials have different insulating characteristics, which affect the ability of the capacitor to hold more or less electrons.

Aluminum electrolytic capacitors are quite common and can hold between 1--10,0000 microfarads and you will find them on many electronic boards. They appear like mini can shapes. 


Electrolytic capacitors, like the one on many circuit boards are generally polarized. You can tell a capacitor is polarized when there are distinct positive and negative sides marked.

Metallic capacitor.


As you can see, there are four capacitors on the Board of Education (image below), two 1000 mF electrolytic capacitors and 2 small yellow or blue tantalum capacitors.


Two large capacitors on the Board of Education, and below these, two small ones.


Capacitors and capacitance have been used in various forms in art and industry for quite some time. If a material has some storage of electrons, then you can say it has capacitance.