ELECTRICITY BASICS

GOT VOLTAGE?

Now, what is this thing called Electricity? If you noticed the similarity between 'electricity' and 'electron', you're way ahead of the game, because electricity is electrons. As you might remember from one of your high school science classes, electrons spend most of their time inside atoms, whizzing around the nucleus in really tiny circles. But not always. Whenever we can get those electrons to leave their atoms and go someplace else, we have electricity.   Electricity, then, is actually the flow of electrons. It doesn't matter if it's a huge number of electrons jumping from one cloud to another in a lightning bolt, or a much smaller number passing through your flashlight bulb on their way from one battery terminal to the other. Anytime we have electrons going form one place to another, that's electricity.
 

This flow of electricity is called Current, just like flowing water is called current. We measure the amount of water flowing through a hose in gallons per minute. Electrons don't come in gallons, but we could measure the flow of electricity in a wire by electrons per minute. The only problem is that the number would be so large, it would be tiring to write all the zeroes.  There was a very smart Frenchman named Andre Marie Ampere who did electrical experiments around the same time as Ben Franklin and his kite. Ampere figured out how to tell if one current was stronger than another, by seeing which one created the most movement in a compass needle. The amount and measure of electrons flowing is called an Ampere, we shorten it to Amp.

Using our comparison with water flowing through a hose, one of the things to consider about that water is its pressure or force. This is different than the amount of water. You see, you can have a thin stream of water coming out of a small nozzle at very high pressure, or you can take the nozzle off and you'll have more water coming out, but with less force. Then again, you could have a fire hose, with much more water but still keeping it at high pressure. And if you close the nozzle altogether, there is no water flow at all but there is still water pressure in the hose.  A Volt then, measures electron pressure or force. Basically, it's not how many electrons there are, but how badly the want to get from one place to another, that determines the voltage.  More specifically, its' the difference in pressure between on point and another. You can't measure voltage at just on point. you have to look at two pints, and measure the difference between them.
What if you have a whole lot of water flowing, and it's also under very high pressure? How do you measure that combination? If you thought of Hoover Dam, that will give you a clue. The combination of water current and water pressure determines that water's power. It's the same with electricity, the combinations of Amps and Volts determines the amount of electrical power. The unit we use to measure electrical power is the Watt.

 This brings us to the concept of a circuit. A circuit is any combination of objects that allows electricity to flow. For example, a battery by itself is not a circuit; there is no flow of electricity. Attach a wire from one end of the battery to the other though, and you have a circuit and electricity will immediately flow.
There are two different ways that electricity is produced, and they are used in most cases for very different purposes.  The first and simpler type of electricity is called direct current, abbreviated "DC".  A voltage is created, and possibly stored, until a circuit is completed. When it is, the current flows directly, in one direction. In the circuit, the current flows at a specific, constant voltage.

 The other type of electricity is called alternating current, or "AC". This is the electricity that you get from your house's wall and that you use to power most of your electrical appliances.  The electricity is not provided as a single, constant voltage, but rather as a sine wave that over time starts at zero, increases to a maximum value, then decreases to a minimum value, and repeats.  So why does standard electricity come only in the form of alternating current? There are a number of reasons, but one of the most important is that a characteristic of AC is that it is relatively easy to change voltages from one level to another using a transformer, while transformers do not work for DC.  Another reason is that it may be easier to mechanically generate alternating current electricity than direct current.

Electrical Components

There are several important basic electrical components that are commonly found in the circuits of virtually all PC parts and peripherals. These devices are the fundamental building blocks of electrical and electronic circuits, and can be found in great numbers on just about everywhere in the PC that is a circuit board. It is useful to know a bit about how they work, and this page will at least provide you with a basis for recognizing some of what you see on those boards, and perhaps understanding the fundamentals of circuit schematics. Bear in mind when reading the descriptions below that it would really take several full pages to fully describe the workings of most of these components.

Battery: A direct current electricity source of a specific voltage, used primarily used primarily in small circuits.

 Resistor:  The main purpose of this is to reduce the flow of electricity in a circuit. Resistors come in all different shapes and sizes.  Generally, bigger resistors can handle more power.
Capacitor:  A capacitor is a component made from two conductive plates with an insulator between them. The insulator prevents the plates from touching. A capacitor stores voltage as electrical energy and blocks DC while letting AC pass.  Charges will remain until the capacitor is discharged when power is off or manually.

 Inductor:  An inductor is essentially a coil of wire. When current flows through an inductor, a magnetic field is created, and the inductor will store this magnetic energy until it is released. In some ways, an inductor is the opposite of a capacitor. While a capacitor stores voltage as electrical energy, an inductor stores current as magnetic energy. Therefore, capacitors block DC current and let AC current pass, while inductors do the opposite.
Transformer:  A transformer is an inductor, usually with an iron core, that has two lengths of wire wrapped around it instead of one. The two coils of wire do not electrically connect, and are normally attached to different circuits. One of the most important components in the world of power, it is used to change one AC voltage into another.  Transformers are one of the main reasons we use AC electricity in our homes and not DC: DC voltages cannot be changed using transformers. They come in sizes ranging from small ones an inch across, to large ones that weigh hundreds of pounds or more, depending on the voltage and current they must handle.

 Diode:  A diode is a device, that restricts the flow of current in a circuit to only one direction; it will block the bulk of any current that tries to go in a wire. Diodes have a multitude of uses. For example, they are often used in circuits that convert alternating current to direct current, since they can block half the alternating current from passing through.
Fuse:  A fuse is a device designed to protect other components from accidental damage due to excessive current flowing through them. Each type of fuse is designed for a specific amount of current. As long as the current in the circuit is kept below this value, the fuse passes the current with little opposition. If the current rises above the rating of the fuse--due to a malfunction of some sort or an accidental short-circuit--the fuse will "blow" and disconnect the circuit. Fuses are the "heroes" of the electronics world, literally burning up or melting from the high current, causing a physical gap in the circuit and saving other devices from the high current. They can then be replaced when the problem condition has been corrected.  All fuses are rated in amps for the amount of current they can tolerate before blowing; they are also rated for the maximum voltage they can tolerate. Always replace a blown fuse only with another of the same current and voltage rating.