# A Crash Course in Electronics: Basic Electrical Theory

Voltage, current, resistors, capacitors, diodes and transistors – Oh my!

This article will examine each basic circuit element from a conceptual standpoint only. Except where absolutely necessary, all math has been omitted so we can concentrate on understanding why these elements behave as they do. Once you understand that, the math will come much easier.

Throughout all your study of electronics, think of electricity as though it were water flowing through a hose. It’s surprising how far this analogy will get you in electronics. Voltage would be represented by the water’s pressure, and Current by the actual amount of water in the hose (rather, the rate of flow). For water, this is usually gallons/min or Liters/min. For electricity this is Amps (Coulombs / second, where a Coulomb is simply a unit of measure for electrical charge) 1, 2

Circuit elements like Resistors, Capacitors, Diodes etc, affect the flow of current through the wire. Let’s look at some of the basic, and most common, components you might have heard about.

Resistors

Resistance is the measure of a conductor’s impedance to current flow. A “resistor” then, is a component with a known resistance. This resistance uses the units of ‘Ohms’, after the German physicist Georg Ohm.3 This resistance is marked on the resistor itself with a code composed of a series of colored stripes.

(See a picture of a 330 Ohm resistor here: http://www.dragonmodz.net/images/resistor.gif, from the DragonModz website)

Capacitor

Capacitors have a multitude of uses in electrical and electronic circuits. In their simplest form they act to reduce high frequency noise or voltage spikes, helping to keep the output voltage signal constant. In this way they are very similar to the shock absorbers on a car.

Capacitors can be used to tune a resonant circuit such as a radio tuner. Some larger units can actually be used as short-term batteries, to keep a circuit running during brief power losses.4

Diodes

A diode is the simplest of a family of devices known as ‘semiconductors’. These devices are so named because of their unique ability to conduct electricity only under certain conditions.5

In the case of a Diode, current is only allowed to flow in one direction, from the Anode to the Cathode. Think of them like a one-way valve in a water pipe.

The circuit symbol of a diode (a triangle very similar to the ‘play’ button on a DVD remote) makes it easy to remember which direction in which current will flow.

Transistors

Ah, yes. The belle of the ball. The Transistor has been at the heart of nearly every technological advance since the 1950’s. So what is it, and why do we care?

Transistors are amplifiers, and can operate in either digital or analog mode.

In digital mode, they closely mimic the behavior of a light switch. You flip the switch and current flows through the switch, causing the light to turn on. The switch itself is either on or off (no intermediate position), and thus the light is either on or off.

In analog mode, they more closely resemble a dimmer switch. With such a switch, the position of the wiper will dictate the brightness of the light.

There is a wealth of information on Transistors, and a quick internet search will return more hits than could be read in a lifetime.

Just understand that they are inexpensive compared to mechanical switches, last longer, and operate many times faster. Literally millions of them can be found on your computer’s main processor, for example.6

Conclusion

So there you have it! If your curiosity is piqued, if you have more questions than when you first started reading this, then I’ve done my job.

This article is intended only to scratch the surface on these devices, and to arm you with just enough information to ask intelligent questions. There is a huge amount of information and tutorials of all shapes and sizes available to you if you’re interested.

References:

1 1 Coulomb = 6.241 509 629 152 65×1018 elementary charges. http://en.wikipedia.org/wiki/Coulomb

2 1 Ampere = 1 Coulomb / Second

http://en.wikipedia.org/wiki/Ampere

3 Georg Ohm was a German physicist who determined the now fundamental relationship between Voltage, Current and Resistance known as Ohm’s Law. http://en.wikipedia.org/wiki/Georg_Ohm

4 More information on general capacitor use and calculations can be found here: http://en.wikipedia.org/wiki/Capacitor

5 Diodes – http://en.wikipedia.org/wiki/Diode. If you’re really feeling adventurous, http://en.wikipedia.org/wiki/Semiconductor

6 Transistors – history, uses, etc: http://en.wikipedia.org/wiki/Transistor