Monday, December 7, 2009

Making sense of bad electronic notation

One thing that used to really bug me about electrical notation is that electron flow is actually going in the opposite direction of the conventional current notation. The current is typically shown moving from the positive terminal to the negative terminal in conventional current notation. However, the electrons are actually moving from the negative to the positive terminal.

The problem is, when Ben Franklin came up with labels 'positive' and 'negative' it was a clever guess. What are the odds of being wrong about current flow? 50/50? By the time people figured out the details, the counter-intuitive notation had firmly cemented itself in electric nomenclature. :)

Anyway, counter-intuitive notation is confusing to me, so I finally came up with a work-around of making sense of conventional diagrams. Instead of thinking of a circuit as an electron-powered device, you can also think of a circuit as a vacuum-powered device. Then the positive terminal has a "surplus of vacuum" as compared to the negative terminal.

If two sealed jars are connected by tube, the difference in air pressure between them represents the voltage. The one with the lowest pressure would be the positive end (which can be seen as driving the system). The actual number of particles flowing through the tube would be the current (amps).

The Amps, Volts and Resistance are somewhat circularly defined. Ideally, a pressure difference of 1 Volt will allow 1 Amp of current (6.242 x 10 ^ 18 charge carriers / sec) to move through a tube with 1 Ohm of resistance.

I suppose, it doesn't really matter as to the direction of the current in a circuit, as long as the notation is consistent. In some cases, it might be easier to visualize something as a vacuum-powered device rather than an electron-powered device. Just like it's sometimes easier to think in terms of 'conductance' vs 'resistance' -- as two sides of the same coin.

2 comments:

KW said...

that sort of clears it up a little. i'm still confused

sevkeifert said...

My analogy isn't the best. For the most part it's just bad notation. :)