Fuel of Hard Knocks: Electricity in a Nutshell
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Let’s take a closer look at our aluminum atom.
Some of the hopping-about activity we just described takes place in a length of aluminum wire sitting on a table. You don’t need to plug it in – the energy inherent in the average room is enough to excite the electrons. The valence electrons in the aluminum migrate back and forth from one atom to the next.
Now, you can kick things up a notch by introducing a battery into the situation. If you connect one end of your wire to the positive end, and the other to the negative end, those free electrons in your aluminum will begin moving, all in the same direction. The battery has an excess of electrons on the negative terminal and lack of them on the positive, so the negative side pushes the negatively-charged particles into the aluminum and the positive side pulls them out. The aluminum conductor provides the highway for the electrons to travel on. This creates a circuit of streaming electrons. Voilà: electricity to fuel your radio or flashlight.
In truth, “streaming” is not the best word to describe what the electrons are doing. The verb used by scientists is drift – and for good reason. In the current lighting up a household light bulb, the electrons are taking their sweet time, moseying along at only a few inches an hour! (The fact that they can power your mixer is due not so much to their speed as to the vast quantity of electrons that are moving.)
PHYSICS FACTOID: Free electrons in a current travel along the surface of a wire, because they repel each other as much as possible as they move toward the positive charge. This is called the “skin effect.”
Why such slowpokes? The problem is that it’s a veritable demolition derby out there, with electrons bumping into atoms (or other free electrons) in their attempt to answer the siren call of the battery’s positive charge. That’s what’s called resistance. The atoms are all the more difficult to avoid because they won’t sit still: Electrons still in their orbit are busy circling their nuclei, and the nuclei themselves vibrate somewhat. As a result, the electrons get knocked off course frequently. The energy they give off in the process is not electricity, but heat – a big problem for our Spark Kent. That’s why the electric wires in your house would be slightly warm to the touch if they weren’t wrapped in insulating plastic. So heat is a byproduct of electricity that is sometimes desirable (in electric blankets or stoves) and sometimes not (in computers and other electronics). To see this concept illustrated, check out this interactive tutorial on resistance.
The collisions contribute to another important inefficiency to these currents. Electrons tend to take the scenic route. Imagine a guy from Tallahassee who wants to go see his new girlfriend in Los Angeles. His car is in the shop and he’s reduced to hitchhiking (he’s a desperate man), so instead of shooting straight down Interstate 10, he must settle for whatever ride he can get. He ends up zigzagging up to Birmingham, then down to Biloxi, then back up to Little Rock, then backwards to Memphis, then down to – well, you get the picture.
The bottom line of this electron behavior is about a 7 percent loss of potential current. As you might imagine, billions of dollars could be saved every year in the United States alone if not for that loss. Wouldn’t it be super if someone could find a way around that?
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