How Wrong Is VERITASIUM? A Lamp and Power Line Story

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]

This discussion seems to revolve around Veritasium's video explaining how elecitricty doesn't quite flow inside of power lines. I can't help but feel that "electricity doesn't travel along the wires" is a somewhat unhelpful "well, actually" explanation that kind of misses the point. And you can tell it misses the point because you can't actually carry electricity without free electrons. And at least in part the confusion seems to focus itself around the concept of stray capacitance, which makes it doubly confusing when you illustrate it with circuit diagrams where stray capacitance is deliberately left out. See also ElectroBOOM's rebuttal [1] where he illustrates how the situation can be explained by explicitly drawing in the stray capacitance. [1]: [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]

Not really in the intuitive sense: [this video] Someone actually went out and tested this: [link] The electric field is very tightly constrained around the wire. The amount of energy that reaches the light through the gap is incredibly small, not nearly enough to turn on a real light bulb. The bulk of the energy does indeed have to take the path through the wire. I find that video usually leads people to an even less correct understanding than the marbles-in-a-tube analogy. The Veritasum video can essentially be summarized, "fun fact: two parallel wires act like an antenna, and an extremely small amount of energy reaches the other end before the rest of the energy takes the long path through the wire.