In your last lesson you learned a lot about the transformer

The transformer is an example of a specific use for two coils

In lessons prior to the one on transformers you studied the coil

You learned that as current changes through the coil

The magnetic field around the coil reacts to this change

Your lesson today deals with another electronic component: the capacitor

Its function is almost exactly opposite from that of the inductor

But between the two there are certain similarities

The capacitor, like the inductor, temporarily stores energy

However, while the inductor stores energy in its electromagnetic field

The capacitor stores energy in an electrostatic field

An electrostatic field can be defined as a field of force between two electrically charged bodies

This definition gives you an insight into the construction of a capacitor

The capacitor will appear in many varied shapes and sizes

But regardless of its physical size or shape you can be sure that it consists of two plates separated by a dielectric

Dielectric is the term applied to the insulating material between the plates of a capacitor

While the plates themselves are of a conductor material

The dielectric could be one of several materials such as oil, paper, mica, or even air

This capacitor uses air as a dielectric between the plates and is a variable capacitor

The symbol for a variable capacitor is the normal capacitor symbol with an arrow drawn through it as is shown here

This indicates that the value of the capacitor can be changed

This type of capacitor with air as the dielectric and with these movable metal plates is used where you want to tune a circuit

Now, if you've ever looked into a radio I'm sure you've seen this type of capacitor

Remember, the air dielectric capacitor is constructed of movable metal plates and is used for circuit tuning