[montecarl]

Awesome notes. I haven't had my coffee yet so perhaps I'm just misreading this part:

"In 1746 Benjamin Franklin mistakenly assigned a negative value to the charge carriers that we now call electrons."

Shouldn't that read "mistakenly assigned a _positive_ value to the charge carriers that we now call electrons"?

[lilgreenland]

Nope! It's kinda silly. We all call electrons negative because of how they were labeled 250 years ago. If he had labeled them positive the math involving electric current would be a bit easier.

https://xkcd.com/567/

[esmi]

I’ve been hearing for years that the math involved would be easier if we switched signs on the electron but what equation specifically would be simpler? One would still have to deal with both polarities. I tutored electrical engineers for years and the biggest misconception by far was always considering the amount (or movement) of charge and the number of particles to be equivalent. Polarity was never really an issue.

[lilgreenland]

A couple things off the top of my head from teaching high school physics:

It would make the direction of current the same as the flow of charge.

It would make electric fields predict the force on electrons.

It would make the right-hand rule for magnetic fields work for electrons and instead of the left-hand rule.

[esmi]

But existing theory predicts all those just fine, it just happens that some things are not in the same direction, but it’s not like one can ignore direction. The math is still always there. And I argue things going in different directions is a feature, not a bug, because it reinforces the point that net charge and net particles are not the same thing.

[SiVal]

Right, the math is the same. We face this in physics all the time. You drop a ball and it accelerates downward. Should the distance it covers be a negative number? Well, it seems linear distance should be positive, but if it is, then does down become positive? Shouldn't up be positive? Or do we reverse from end-minus-start and make it start-minus-end?

It doesn't matter. The math is all the same with just different labeling conventions.

For the general physics of electric charges, the convention that a proton is +1 and electron is -1 is somewhat useful as a reminder of the larger range of phenomena: protons carry charge, too, and a movement of positively charged molecules makes the charge carriers and current move in the same direction.

But as soon as you start working with practical, artificial electrical circuits (as opposed to, say, neurons), the electron-is-negative is a nuisance, because the charge carriers are almost always simple electrons. To visualize "stuff" moving one way, you have to visualize "other stuff" moving the opposite direction. You have to keep thinking that when you add more you get less. Visualization of electric/electronic technology would have been a lot more convenient if the convention had been that electrons were positive, protons negative.

[esmi]

We're probably going to have to agree to disagree on this one as I just don't see the nuisance and I see some positive aspects to the existing convention which I highlighted previously.

The classic, and really intuitive, experiment that requires one to understand the movement of both the carriers and the charge at the same time is the Haynes Shockley experiment [1]. It has not been my experience that charge convention gets in the way of students interpreting this experiment.

For the vast majority of practical (artificial?) electronics, when designing one only needs to look at the movement of net charge. Passive sign convention (used by spice) is about the flow of charge, not carriers. Maxwell's equations don't even mention the carriers. It's not clear to me why one needs to visualise carriers to design circuits. In my experience (i.e. transmission lines) it can actually hinder students to consider the movement of carriers when designing a practical circuit.

[1] https://en.wikipedia.org/wiki/Haynes–Shockley_experiment [2] https://en.wikipedia.org/wiki/Passive_sign_convention

[lilgreenland]

I see your point.

[analog31]

Or 250 years from now... ;-)

https://en.wikipedia.org/wiki/CPT_symmetry

[klyrs]

I ran into this recently with vacuum tube diodes. There's a cloud of electrons surrounding the heated ground-plate. The source plate is at high voltage. Increasing the voltage on the grid attracts electrons, which stream from the ground and fly towards the "source." And I'm calling it "source" because the stream of electrons flowing from ground to source is a positive current from source to ground. Thanks, Ben