Capacitors

In a way, a capacitor is a little like a battery. Although
they work in completely different ways, capacitors and
batteries both store electrical energy.You know that a battery
has two terminals. Inside the battery, chemical reactions
produce electrons on one terminal and absorb electrons on the
other terminal. A capacitor is much simpler than a battery,
as it can't produce new electrons -- it only stores them.

In this post, we'll learn exactly what a capacitor is, what
it does and how it's used in electronics. We'll also look at
the history of the capacitor and how several people helped
shape its progress.

Inside the capacitor, the terminals connect to two metal
plates separated by a non-conducting substance, or dielectric.
You can easily make a capacitor from two pieces of aluminum
foil and a piece of paper. It won't be a particularly good
capacitor in terms of its storage capacity, but it will work.

In theory, the dielectric can be any non-conductive substance.
However, for practical applications, specific materials are
used that best suit the capacitor's function. Mica, ceramic,
cellulose, porcelain, Mylar, Teflon and even air are some of
the non-conductive materials used. The dielectric dictates
what kind of capacitor it is and for what it is best suited.
Depending on the size and type of dielectric, some capacitors
are better for high frequency uses, while some are better for
high voltage applications. Capacitors can be manufactured to
serve any purpose, from the smallest plastic capacitor in
your calculator, to an ultra capacitor that can power
a commuter bus. NASA uses glass capacitors to help wake up
the space shuttle's circuitry and help deploy space probes.
Here are some of the various types of capacitors and how they
are used.

* Air - Often used in radio tuning circuits.
* Mylar - Most commonly used for timer circuits like
clocks, alarms and counters.
* Glass - Good for high voltage applications.
* Ceramic - Used for high frequency purposes like
antennas, X-ray and MRI machines.
* Super capacitor - Powers electric and hybrid cars.

In an electronic circuit, a capacitor is shown like the
picture.

When you connect a capacitor to a battery, here's what
happens:

* The plate on the capacitor that attaches to the
negative terminal of the battery accepts electrons that the
battery is producing.
* The plate on the capacitor that attaches to the
positive terminal of the battery loses electrons to the
battery.

Once it's charged, the capacitor has the same voltage as the
battery (1.5 volts on the battery means 1.5 volts on the
capacitor). For a small capacitor, the capacity is small. But
large capacitors can hold quite a bit of charge. You can find
capacitors as big as soda cans that hold enough charge to
light a flashlight bulb for a minute or more.

Even nature shows the capacitor at work in the form of
lightning. One plate is the cloud, the other plate is the
ground and the lightning is the charge releasing between
these two "plates." Obviously, in a capacitor that large, you
can hold a huge amount of charge!

Let's say you hook up a capacitor like the picture :
Here you have a battery, a light bulb and a capacitor. If the
capacitor is pretty big, what you will notice is that, when
you connect the battery, the light bulb will light up as
current flows from the battery to the capacitor to charge it
up. The bulb will get progressively dimmer and finally go out
once the capacitor reaches its capacity. If you then remove
the battery and replace it with a wire, current will flow
from one plate of the capacitor to the other. The bulb will
light initially and then dim as the capacitor discharges,
until it is completely out.