ElectroBOOM
4 HN recommenders · recommended in 3 months, 2021–2023
19:17 · 4.4M views · Dec 8, 2021
ElectroBOOM's Mehdi Sadaghdar responds to Veritasium's lamp-and-long-wire puzzle, analysing it as an electrical engineer. He covers where the original framing misleads and the role of stray capacitance.
HN commenters recommend it as the more rigorous, polite and complete treatment of the Veritasium puzzle, though one dissents that the original misleads people.
10 comments from Hacker News
Controversial is fine to the extent the controversy shows people struggling toward clearer understanding and better explanations, and as long as all parties are operating in good faith (i.e. not being deliberately misleading). Let me highly recommend Mehdi Sadaghdar’s (ElectroBOOM) excellent response video this video which does a great job of empirically investigating and theoretically explaining the subtleties involved, in a polite, respectful, and entertaining way. I have similarly enjoyed the exchange between Sadaghdar and Steve Mould about the physics of the “chain fountain”. These kinds of friendly scientific “debates” show viewers (e.g. kids) a bit of how the scientific process and scientific discourse works, in a form that is more accessible and digestible than technical journal papers or history books. Having a discussion back and forth helps to improve both viewers’ specific knowledge and viewers’ processes for comprehending and interrogating new information, so long as the median viewer actually sees some of the responses. (Someone who only ever saw the first Veritasium video probably ends up with a somewhat wrong mental model.)
In my opinion the video made a couple of mistakes, which I think ElectroBoom's response* addresses nicely. Also its proof using the pointing vector to show the flow of energy is misleading; In the video Derek shows that the energy flows toward the lamp when the circuit is already in a stable configuration, but the point of the video is to explore what happens before the circuit reaches that configuration. This is relevant: assume that the right half of the cable is connected to the positive pole of the battery, in a stable configuration every point of the right half of the circuit has a positive charge (creating the poynting vector field as shown in the video) while 1/c seconds after the switch was closed the wire just to the right of the lightbulb will have a negative charge (the cable near it is positively charged from the battery and so the upper cable acts as a the negative half of a capacitor) which changes the direction of the poynting vector. In the end it felt like it was telling you that its message was that energy travels via the fields but what it actually said what that switches cause electric interference. * this video
The veritasium video didn’t create a clear picture of what’s going on and you shouldn’t feel bad for feeling more confused after watching it ElectroBOOM has a good response this video
You should watch Electroboom's analysis if you want the full details from an electrical engineer: this video
> Anything involving the electrical energy not inside wires has no water analogue (ie the electromagnetic waves inside a transformer) You don't even need fancy things like transformers for energy not in the wires to be important. Even a simple DC circuit consisting of a battery in series with a light bulb mostly involves an electromagnetic field to transfer energy from the battery to the light bulb, which mostly takes place outside the wires. The function of the wires when it comes to energy transfer is to carry moving charge which creates the magnetic part of the electromagnetic field that actually carries the transferred energy. Here's a pretty good explanation [1]. That video was from January 2019, and not controversial. Veritasium did a video on the topic in late 2021 that didn't really present things as well and ended up being quite controversial [2]. Other well-known YouTube channels such as EEVblog [3] and ElectroBOOM [4] responded. There was also someone who bought a bunch of wire and did the experiment as described in the Veritasium video (although scaled down). That was discussed on HN and that discussion contains some very interesting links [5]. In particular the link to a talk by Rick Hartley in this subthread is very informative [6]. He talks about how most EMI problems in PCB designs are due to people not taking into account the the energy is not in the wires. [1] [LINK] [2] [LINK] [3] [LINK] [4] this video [5] [LINK] [6] [LINK]