Years ago, “B.C.” (that’s “Before Computers”), we played with different types of toys than kids have these days. Our parents wanted us to “discover” life and learn on our own. That, of course, was when our parents were truly responsible for their children’s safety and well-being and not expecting the Government, schools and attorneys to perform those duties on their behalf. We didn’t really worry about getting cut by the sharp edges of the girders or swallowing the nuts and bolts, any more than we worried about getting hit by a tractor trailer while riding our bikes.
But I digress. The best part of growing up for me was the process of experimentation. Even when I screwed up and got shocked when I disassembled my parents’ clock radio or got hit by one of my CO-2 home rockets, I still had a ball and learned from my little experiments. I had the joy and education of discovery and learning that became permanently imprinted on my DNA and responsible for my success later on in life. I learned early on how to solve problems through my own trial and error and accumulated experience.
My favorite toy was the Erector set. Invented by A.C. Gilbert in 1913 and sold by a company bearing his name, it’s still available today. The key attractions were that (A) you could build something with its metal beams, pulleys, gears and wheels and then take it apart to build something else and (B) it had small electric motors to propel your creations. I confess that I used parts of that set to repair things around the house well into my 30’s. (Apparently so did others – Wikipedia states that it was used to build the precursor to the artificial heart and also Dr. Kevorkian’s first assisted suicide machine. But like some of what I read in Wikipedia, I’m not personally knowledgeable about the veracity of these claims.)
But, again, I digress. My point revolves around the motors and batteries that you could use with your Erector creations. Most of the time I used what was called a “dry cell” type of battery, using “direct” as opposed to household or alternating (“AC”) current. It was a tube about eight inches tall, maybe three inches in diameter, with a screw terminal in the middle of the top and another on the side, used to hold down bell wires (small diameter solid copper wires sheathed in plastic, predominantly used for low voltage applications like doorbells). You were supposed to attach the wires from the motor or switch or whatever, to the positive (red or “+”) terminal in the center and the other wire on the negative (black or “-“) terminal on the side. The closest thing to a dry cell battery these days might be a lantern battery. I could describe more about these batteries, but that isn’t really the point here.
Which is this: Batteries are on or off, nothing in between. Connect the wires to the terminals and the motor runs or the light turns on. Take the wire away, it’s off again. Electricity, more correctly electrons, must always flow in a in a loop (called a “circuit,” like a circle) through a single direction in the wire. If the wire is disconnected from the battery, or there is a break in the circuit (say a squirrel chews through the wire) the electrons stand still and there is no “current” or electricity available to power the device.
More important is the connection between electricity and magnetism. The movement of the electrons through the wire inevitably produces an electro-magnetic field, which can be depicted as a sine (repetitive) wave. Electric current signals are actually waves, which can vary by phase (see voltage, below). A simple experiment we did as kids was to take a length of wire, then wind it in multiple loops around a broom handle (or, even better, a metal object like a bolt), then connect both wire ends to a battery. Viola! The coil became a magnet and could use it to pick up pieces of iron. For a more modern take, see the photo at the right. Once again, the magnet had only two choices: Connected to the battery, it was a magnet. Disconnected, no magnet. [For a little more about magnetism, click BELOW.]
Another example of the relationship between electricity and magnetism is antennas. The example on the left (courtesy Wikipedia), diagrams the electric fields (in blue) and the magnetic fields (in red) of a typical dipole antenna (the vertical black rods in the middle) during transmission.
So electricity and magnets possess only two choices. These choices are actually called “states”; At any given moment in time, it’s either in the “on” or the “off” state. That’s called a “binary system” and it’s the key to computers, which are also binary devices. Why? Because the hard disk drives on which the data is written and stored on computers have thousands of individual areas which store this data in “binary” format. This data, which is “written” to the metallic hard disk on the drive, is actually magnetic. [See Hard Drives for photos; Base-X for more.] That’s why, at least on the older drives, you weren’t supposed to bring a magnet anywhere near it or the magnetic field would disrupt the data written on the disk, erasing the data. Each bit, or binary digit, of data on the disk is either “on” or “off” depending on whether the magnetism is either positive (“+”) or off (“0”). Exactly like the broom handle magnet, where the copper wire is either connected or disconnected to the battery. Expand this occurrence thousands and thousands of times (see bits and bytes for the exact numbers) and you have data storage on a hard disk drive. That’s also why, in the computer registry, the values for each key are expressed in binary form, with “0” standing for “off” and “1” for “engaged”. And, for even more information, read How Computers Compute to see how binary code is used by computers. See, it’s all related! [And to take things up a level, consider computers which can operate in several “states” at the same time (i.e. on, off and everything in between), which are known as “quantum” computers. Click HERE for more discussion about these.]
There are also a few other important properties of electricity other than its binary and magnetic aspects. So, in the interest of completeness, consider:
Electricity has what’s known as “polarity”. Depending on the placement of the wires on the battery, the direction which the current flows can be changed. Kind of like reversing the hands of a clock from clockwise to counter-clockwise. If you reverse the positive and negative wires, the “polarity” will also be reversed. The current will flow in the opposite direction through the circuit. So what’s the big deal? If it’s a lamp, it will probably still work. That’s because some devices, like lamps, have what is known as “unpolarized” paths. They’ll work whichever way the current flows. But in other instances, this can be dangerous. Like phones and electronic devices. This is because the electrons flow between two “poles” (the terminals on the battery, for example) and one of the poles usually has more electrons than the other. The one with more electrons is said to have negative polarity, the other is assigned positive polarity. When the two poles are connected by a conductive path like a wire, the electrons and therefore the current should normally flow from the negative pole to the positive pole. Most more sophisticated devices are designed to handle currents controlled by specific voltage levels in only one direction. So, when you apply that voltage in the opposite direction one or more components within a circuit will literally overheat, short, and conduct current in the wrong direction until they fail. Capacitors can even blow up or catch fire. That’s why in more modern wiring, so-called “polarized” plugs and receptacles have one of the two sides wider and flatter to assure that the current is polarized properly. (In such plugs, the small blade or plug is for the hot wire, the wide blade or plug for the neutral wire.) Applying this to digital communications, the data is composed of short-duration pulses called bits (“binary digits”), each of which possesses either a logic state of 0 (or low) or 1 (high) with corresponding voltages. If both voltages have the same polarity, the signal is called unipolar; if the voltages have opposite polarity, the signal is called bipolar.
Then there’s voltage. Also called electromotive force, this is the electrical force or pressure that causes current to flow through a circuit. It is an expression, in volts, of the potential difference in charge between two points. As the current passes a fixed point over a unit of time, it‘s voltage is measured. The greater the voltage, the greater the flow of electrical current. For example, a flashlight might be 1.5 volts, while an automobile battery might be 18 volts. More about voltage: Standard house current in the U.S. is 120 volts, but in many European countries it is 220 volts. Getting a shock from 120 volts hurts but usually isn’t lethal, while 220 volts probably is. But the disadvantage of the lower U.S. voltage means that you have to have thicker wires to carry the current (see gauge). But European homes are equipped with all sorts of precautions (like fuses in every plug, switches in every outlet and complete grounding) to protect people from shocks, while American homes generally aren’t, even for half the voltage. In the U.S., there isn’t even protection for 500amp 12V auto batteries, which can deliver a powerful jolt. (This is because the more voltage you have for a given amount of available amperage, the more the possible damage). Most U.S. houses are wired from the service pole at the street to 240 volt service, using a three wire, 60 Hz, single phase service. Most inside wiring has two “line” wires on flat (usually polarized) prongs and a center (round) neutral prong in single-phase. This way, there is a 120 Volt circuit between either line and the neutral. But you can create 240 Volts by connecting across the two line wires. In the U.S., 240 volts lines are only necessary for electric dryers, electric stoves and electric heaters and a/c’s.
There’s no such thing as a perfect conductor. You can’t easily pass electricity through glass or wood very well. Even copper offers some resistance to the current, slowing it down slightly. That resistance is measured in Ohms. The higher the number of Ohms, the greater the resistance. The signal may become further attenuated for any number of reasons (see, e.g. dirt, below), making it weaker still.
Also related to resistance, the actual thickness of the wire carrying the current can generate resistance as well. The higher the gauge (diameter), the thinner the wire and the more the resistance. Think of water flowing through a one inch hose having greater resistance and pressure than the same amount of water flowing through a four inch pipe, having much less resistance. Lamp cord is 18 gauge, while speaker wire is perhaps 24 gauge and has higher resistance (but isn’t used to carry much current, so it’s appropriate for that use). Using the incorrect gauge has consequences: When working in construction, I quickly learned that using an extension cord with too high a gauge (remember that, the higher the guage number, the smaller the wire diameter) to connect construction equipment like a saw or a drill may appear to run it but will actually shorten its life and possibly burn it out.
Talking about current, there are two types: Direct, like the current that flows from a battery. And alternating, like household current. Direct current flows only in one direction continuously, while alternating current changes the direction of the current back and forth, say 60 times a second (a/k/a 60Hz). Alternating current allows higher voltages and travels better over long distances, which is why it’s used to supply house current. And, no matter what type of current you’re talking about, it’s almost never perfect and has at least some dirt interference.
Wattage is power, expressed in watts or kilowatts, required to operate an electrical device. Named after Scottish engineer James Watt (1936-1819), it is defined as “joules per second,” a measurement of power consumption or transfer over time. Technically, in terms of electromagnetism (which we’ve been discussing all along), one watt is the rate at which work is done when one amp of current flows through al electrical potential difference of one volt. Clear, huh? Let’s try it this way: A joule is a unit of energy that is equal to the work required to produce one watt of power for one second, i.e. one “watt second”. See the similarity? These are units of power over time, i.e. the amount of power required to operate a device over a second, minute, hour, etc. Therefore, a 100 watt bulb operating for one hour uses 100 watt-hours of 0.1 kilowatt hrs. Similarly, 100 watts of energy would light a 50 watt bulb (or other device) for 2 hours. So, when you see a wattage rating on a device, it means that it requires that level of power over time in order to be operable.
Amperage is a measurement of the strength of an electrical current. The higher the amps, the more powerful the device. For example, you would want to operate a 15.5 amp circular saw over a 9 amp one.
Another interesting attribute of electricity that we sometimes encounter in cabling is resonance. This is a ringing sound that is generated in some electrical installations where the parts of a circuit cancel each other out, sometimes because the collapsing magnetic field (See? Magnetism again!) of an inductor generates an electric current that charges the capacitor, causing oscillations that generate noise and signal distortion. It’s not a good thing for communications circuits, because it can result in noise, signal distortion, even damage to circuit elements. See also THD.
A little more about magnetism: There isn’t much in this site about magnetism, so I’m putting this useful little gem here. You may have heard people to tell you not to get a magnet near your computer because it’ll erase your hard disk drive. Or a hotel concierge may tell you not to keep your magnetic room card near your cell phone because the magnet in the phone could erase it. Fact or fiction? (Actually, fiction.) Maybe the original hard drives could have been erased by a powerful magnet in very close proximity, but nowadays they’re shielded and even putting a magnet on top of an open drive won’t erase it. I know, I’ve tried. Same for cell phones, there just isn’t nearly enough power to erase even a magnetic strip on a card. Magnetism strength is measured in “gauss”. (That’s why the older CRT monitors, which had more magnetic properties, had to be periodically degaussed.) By way of comparison, an MRI machine produces 15,000 gauss. Most household items that are magnetic, like refrigerator magnets, produce between 0 and 100 gauss. A cell phone’s magnetic field produces 1.2 to 10 milligauss, making it almost impossible to erase a mag card. See the glossary definition at rare earth metals for a discussion about high powered magnets.
Conclusion: There’s always more, but these are the basics. The point has been to show how electricity, magnetism and binary computer systems fit together...