Basic Facts About Capacitors And Inductors

Unit Of Capacitance Is The Farad, Inductance Is The Henry
Michael Faraday 1791 to 1867
Picture of Michael Faraday who lived from 1791 to 1867 Mr. Faraday's and Joseph Henry's work on the magnetic field around a conductor carrying current gave the concept of the electromagnetic field. Michael Faraday's use of the old large "Leyden Jar", a very early form of glass capacitor used to store electric charge, led him to develop smaller capacitors with greater capacity to store electric charge. This alowed him to work on electromagnetic rotation (the principle behind the electric motor). The electromagnetic field and the electric field are two of the most important concepts in electronics. The unit of capacitance, the farad, is named in his honor.
We're not going into great detail here about the complete electric properties of capacitors and inductors since it involves alternating current theory and that is too big a topic for this small article, but if you are interested in learning more about capacitors and inductors then check out
Starting With The Capacitor...
A capacitor is made up of two metal surfaces that face each other and are insulated from one another.
The basic symbol looks like this Basic Fixed Capacitor
If you put you put a source of voltage like a battery across the capacitor what would happen? Well, since the two plates are insulated from each other nothing will happen. Actually, if you measured current flow in the circuit you would find a small amount of current would flow for just a brief moment.
This is because a capacitor can hold a electric charge. It is stored as an electric field between the two plates and the current flow was the capacitor storing that electric field.
The amount of energy the capacitor can hold depends on it's value (farads) and that is determined by the area of the plates, the separation between the plates and the insulating material between them.

Capacitors are measured in Farads or more commonly in micro farads and pico farads. The name comes from Michael Faraday (1791-1867), a very interesting man. Read some about him when you get the chance.

Coils and Inductance

Joseph Henry (1797–1878) an American scientist was also working with electromagnetic induction about the same time as Michael Faraday was in England. Henry's work led to the electromagnet. The unit of inductance, the henry, is named in his honor.
An inductor is a lenght of wire wound into a coil. Sometimes on an iron form or without depending on the amount of "inductance" desired. The more turns of wire on the coil the higher the inductance or using an iron core will result in more inductance.

Inductor with an air core is air core inductor

Inductor with an iron core Iron Core Inductor

Inductance is measured in henrys and more often in micro or pico henrys.
What will happen if you put you place a source of voltage, like a battery, across the inductor like we did with the capacitor?
Watch closely... it acts the exact opposite of the capacitor! For a very brief moment (depending on the amount of inductance) nothing will happen, then current will begin to flow and the only thing limiting the current will be the internal resistance of the coil.
The inductor stores energy in a magnetic field. The capacitor uses an electric field. When current flows through an inductor a magnetic field is formed around the inductor. When that current stops, the magnetic field collapses back on the inductor and generates a reverse current. A capacitor stores a voltage (electric charge) as an electric field, when the voltage is removed the capacitor tries to maintain that voltage.

Remember, a changing current creates a changing magnetic field and a changing magnetic field creates a changing current.
Important Points Capacitors and inductors perform many functions, but here are the basics...

1. The capacitor tries to keep voltage constant.
2. The inductor tries to keep current constant.

Later on you'll see how the combination of the capacitor and the inductor together make "magical things" happen in electric circuits.