Hacker News Reader

Comment by dekhn | Hacker News Reader

Few, if any; instead, it's typically the propagation of an electromagnetic wave that transmits a signal: https://en.wikipedia.org/wiki/Speed_of_electricity

View on HN

This veritasiun is relevant, complete with reddit discussion:

https://www.reddit.com/r/engineering/comments/qxrsrp/the_big...

What if you made a really big circuit consisting of a battery, switch, lightbulb, and a wire that goes out 300k km on either side making a circuit that should take 1s at the speed of light to travel through. How long after closing the switch will it take for the light to go on?

“Few”, yes. But definitely some. I don’t think you can have propagation of EM wave through a conduit without at least pushing one electron into the conduit and removing one electron from the other side of the conduit.

Yes, but it's subtle; see https://en.wikipedia.org/wiki/Drift_current and https://en.wikipedia.org/wiki/Drift_velocity and https://en.wikipedia.org/wiki/Electron_mobility for more details

I was pretty surprised about this since I had mistakenly believed that electrons had a velocity near the speed of light, which I think is only true in particle accelerators.

Indeed - I thought most college Physics 2 courses teach that electrons actually move quite slowly through conductors. It’s the “wave” which propagates near the speed of light, not the particles.

My mistake was being a biologist, and skipping or sleeping my way through the EE part of physics :) and then saying the wrong thing in front of some very smart people

Lord, I make that mistake on HN nearly every month. At least you didn’t have a “Putnam award” moment:

https://news.ycombinator.com/item?id=35079

I've had something similar- when I was deciding what grad school to go to, I was explaining how RNA enzymes work to some professor at UC Boulder, who ended up being Tom Cech (who won the Nobel for discovering RNA enzymes); he had to correct a lot of the details I messed up. I ended up going to UCSF and fortunately didn't try to explain prions to Stanley Prusiner.

In short, nearly everything I have learned is from saying dumb things in front of very smart people who instantly understood my misunderstanding and knew exactly how to explain it so I understood. That includes Sanjay Ghemawat and Jeff Dean telling me "your idea isn't so good, it's n-squared, here's a linear solution"

https://youtu.be/2Vrhk5OjBP8?si=gDXZKYeFkVoAs_LG

AlphaPhoenix did an amazing experiment to measure the speed of electricity FWIW. His other videos are incredible as well and explain EM physics in an absolutely outstanding way.

what is the electromagnetic wave made of, what's the substrate it is composed of and moving through?

The wave is electromagnetic energy passing through a waveguide (typically copper) mediated by electrons. See https://en.wikipedia.org/wiki/Waveguide

Reply on news.ycombinator.com