Everyone who’s taken physics at some point knows about the Right Hand Rule. There are two versions. If you have a wire carrying an electric current, you point your thumb in the direction of the current and your fingers “curl” in the direction of the magnetic field.
The other version is that if you have two out of the following three — current, magnetic field, and a force — the right hand rule can help you find the direction of the third one that gets induced from the other two:
Well, there’s one really annoying thing about this rule: it requires the current to be moving positive charges! Well, positive charges do move in electric circuits.
A typical example: for every 100,000 negative electrons that move one direction in a circuit, there is one positively charged iron nucleus that moves in the opposite direction. But the reason we use the convention that positive charges move is, hundreds of years ago, there was no way to tell which charge was moving!
Ben Franklin guessed. He had two possibilities, positive and negative. And he guessed wrong. But somehow, hundreds of years later, we’re still using his incorrect guess. It drives electricians nuts, because they’ve switched over to using negative electrical currents, but physicists haven’t. Is there a way to fix this?
It isn’t hard, all you have to do is use your left hand instead of your right! Same deal, too. Thumb=current, index finger=magnetic field, and middle finger=force. Well, physicists are slow to change their conventions, so perhaps xkcd can help effect change with their comic today:
Really, isn’t physics confusing enough without having to deliberately correct for a mistake we know we’re making? Or is it that hard to change an educational convention?