Capacitors in some ways are sort of like batteries in the sense that both batteries and capacitors store electric energy, however they work in completely different ways. Everyone knows that batteries have two terminals and inside of them are chemical reactions that help to create electrons on one of the terminals and then absorb electrons on the other terminal. A capacitor however, is a lot simpler than a battery, it is not able to produce new electrons, it can only store them.

Inside capacitors you will find that the terminals are connected to two plates of metal and they are separated by a substance that is non-conducting or dielectric. Capacitors can be made quite easily by taking two pieces of foil and one piece of paper, it won’t be a real good one but it still will actually work.

The theory is that the dielectric can be any kind of substance that is non-conductive. Specialized materials are used that will suit the function of the capacitors. Such materials can be mica, ceramic, porcelain, Mylar, Teflon or cellulose. Sometimes air can even be used as a non-conductive material. The dielectric will dictate what kind of a capacitor it is and what it is best suited to be used for. It will depend on the size of the capacitor and the type of dielectric. Some of them are best for high frequency use and others are better for high voltage use. They can be made to serve just about any purpose from very small plastic capacitor in a calculator to a huge capacitor that can power a bus. NASA used glass capacitors to wake up the space shuttle’s electric circuitry and to also help in deploying space probes. Other uses are:

Air – Most often used for radio turning circuits.
Mylar– Most often used for timer circuits such as counters, alarms and clocks.
Glass– Often used for high voltage applications.
Ceramic– Often used for high frequency items like antennas, MRI machines and X-ray machines.
Super Capacitor– This powers electric and hybrid cars.

Here is what happens when you connect a capacitor to a battery:

  • A plate that is on a capacitor will attache to the negative terminal that accepts the electrons that it produces.
  • Then the plate that attaches to the positive battery terminal loses electrons to the battery.

Once the capacitor is charged it will end up having the same voltage as the battery has. So if the battery has 1.5 volts so will the capacitor. A small capacitor will have a small capacity and a big capacitor will be able to hold a much bigger charge.

Capacitors work sort of lightning. One of the plates is like a cloud and the other plate is like the ground and then the lightning is the charge that is released between the two plates.

If you have a light bulb and a capacitor that is reasonably big you will see that when it is connected to the battery, the bulb lights up as the current flows from the battery to the capacitor. Once the capacitor has reached its total capacity the bulb will begin to dim and then finally will go out.

The storage potential is called capacitance and this is measured in units called farads. A 1-farad capacitor is usually pretty big and could be the size of a tuna can or even a 1-liter soda bottle. Since farads are so big it is not very practical to use capacitors for anything other than high voltage use.
The advantage capacitors have over batteries is that they can dump all of their charge in just a fraction of a second whereas batteries can take minutes to completely discharge. This is one reason why flash on a camera will use a capacitor.

Some ways in which capacitors are used:

  • They can be used to store charges for high speed use such as camera flashes and big lasers.
  • They can be used to eliminate ripples in a DC voltage that might have spikes in it. Big capacitors can even out the voltage by absorbing the peaks.
  • They can be also used to block DC voltage.