In school, you might have learned that electrons were negatively charged and protons were positive. This is not a fact of nature but a human-invented convention. It’s a fact that protons and electrons have opposite charges, but scientists could just as easily have named electrons positive and protons negative. Everything could have been set up to be much easier. We now teach students that electric current flows from positive to negative, even though we know electrons are moving the opposite direction to the current. Why not call electrons positive and define the direction of current so that it coincides with the direction of these positive electrons?
I started wondering whether we owe the weird backward definition of electric current to Benjamin Franklin, since he initiated our convention of calling opposite electrical charge positive and negative. Franklin’s “one fluid” theory held that electricity flowed within and between objects – excess fluid making some objects positive and a dearth of fluid making others negative. Charge could be moved around but not created or destroyed.
Did Franklin get things backwards? To find out, I needed to find the right historians. We in Philadelphia have the premier museum devoted to the history of chemistry with our Chemical Heritage Foundation, and I soon discovered that Minneapolis has the premier museum devoted to electricity. It’s called the Bakken Museum. I emailed them my question about the origin of positive and negative charges, and soon received an answer from Justin Spencer:
Excellent Question!There is two common ways to think about the flow of electricity in a circuit. 1) Current flow from the positive to the negative terminals of the battery, typically taught in classrooms before the idea of charged particles are introduced. 2) Electron flow, where electrons come out of the negative terminal of the battery and flow to the positive terminal of the battery.
As far as the history goes, Ben Franklin imagined electricity as a type of invisible fluid that could build up or be absent from a material, or at least certain materials. He believed that when this invisible fluid built up the object was positively charged. When there was an absence of this fluid he called that material negatively charged. It turns out he got the concept right but the nomenclature backwards.
That is my interpretation anyway. A more thorough explanation can be found on Wikipedia at http://en.wikipedia.org/wiki/Electric_charge#History .
Of course, we can’t blame Franklin for getting it backwards. It would have been anyone’s guess which way the “fluid” was flowing before electrons were discovered. But the way Franklin guessed made things confusing, since, according to the Wikipedia article, he decided that electrical fluid was going into glass when it’s rubbed with a cloth.
We now know glass loses electrons when it gets charged – something flows away from it. So we can still keep Franklin’s convention by continuing to say glass gets positively charged, as long as electrons are defined as negative.Alberto Martinez, a historian of science at the University of Texas and says we should change the whole thing to make it easier. He may be right. Physics is hard enough with all the counter-intuitive weirdness of quantum mechanics. Why not at least make the part we can control streamlined? On the other hand, we’ve been doing things this way for a long time. Perhaps changing this could make things even more confusing.