Negative discrimination

5th March 2004 at 00:00
We all know what happens when we connect a light bulb to a battery. Current flows from the positive terminal, through the filament and back into the negative terminal - right?

Wrong. The stream of electrons that we call electricity actually travels in the opposite direction. This hardly matters in the case of a bicycle lamp, but it can make all the difference in a complex electronic circuit.

How did this confusion arise? It's all down to Benjamin Franklin, the otherwise blameless American scientist, statesman and general all-rounder.

Nobody knew about electrons in the 18th century. But it had been known for centuries that if certain materials were rubbed together, they would become mutually attractive.

Franklin speculated that when wax was rubbed with woollen cloth, an invisible fluid was rubbed off the wax and on to the wool. In this way, he argued, the wool became positively "charged" with the fluid, while the wax was now deficient in it, and it was this imbalance that caused the attraction. Franklin was right about the rubbing, in that it does cause a transfer of matter - not a fluid, but minute particles called electrons.

But he was quite wrong in one important detail. When wax is rubbed with wool, it gains electrons from the fabric. Unfortunately, by the time scientists worked this out, it was too late. The idea that the wool became positively charged and the wax negatively charged had taken root. The answer, clearly, was to designate electrons as a "negative" influence. And that is what happened.

Today, convention insists that electrons are negatively charged, and that they travel in the opposite direction from the way they actually do travel.

Components and circuit diagrams are labelled with entirely misleading arrows, and somehow the whole fiction is made to stand up.

Meanwhile, students learning electronic theory for the first time are often hopelessly confused, and many are reluctant to accept a convention that they know to be a lie. But what is the alternative? To ditch Ben Franklin and re-designate electrons as positive?

Sometimes, it's easier just to go with the flow.

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