Propagation of energy through the EMF

Earlier today in Rugby’s Weekly Google Meet, Ryan (@ipeverywhere) mentioned the recent Veritasium video (linked below) and wondered if it had any implications for discussions of cables and audio.

Not knowing the answer I thought I would open this thread and link some relevant videos to spark discussion:

My first exposure to these ideas of classical electrodynamics was The Science Asylum.

This is the recent Veritasium video.

This RSD Academy video and follow up and second follow up continue the discussion.

And then this point of contention from Tycho, who asks a lot of the questions I had.

Edit: As I understand it, Tycho is suggesting that the time to light the bulb will be 1 second rather than 10 exp -9 seconds.

Time to turn the thought experiment into an actual experiment and see with whom the real world agrees.

Edit: Another doubter.

Edit: It’s 1/c with a sensitive bulb but grows brighter later.

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Thanks Andy! As a physicist, I found this fascinating. I didn’t watch all videos, just Veritasium and Tycho, and based on my own knowledge, I have to give it to Tycho. For one, Veritasium takes the properties of a stationary system and applies them to a dynamic one. Then, it’s obvious that wires play a crucial role in energy transmission (that’s easy to explain intuitively, but it would take a while) so their length does make a difference. Bottom line, I don’t think this changes current understanding of cables.

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Electroboom… It’s good

I’m still gather on my thoughts on how this impacts our precious audio cables :slight_smile:


My new ‘VapourField’ cables consist only of the space which was once around some very expensive wires. The space is carefully stripped from the wires, retaining all inherent field characteristics. It is then shipped to you in a well packed box with lots of bubble wrap and foam beads and you apply it to your audio equipment. Sadly I cannot accept liability should you fail to apply the space correctly. All this for the amazing price of only twice what you imagine.


Derek at Veritasium has released a follow up video which includes a physical experiment, as distinct from a thought experiment.

The explanation in this latest video is much more convincing, as is the result of the experiment. The simulations showing spherical propagation of the change when the switch is closed really brings home that the energy is in the field.

Watched the video. Derek’s initial point was that the bulb will light up almost instantly. Now, the conclusion was that the bulb receives a very small amount of energy fast, with the full amount coming later, when the field finishes propagating through the wire. At the end of the day, he was still wrong (it’s nice he admits that much) and he’s just trying to save face. Yes, the field propagates outside the wire, and that happens regardless if the loop is closed or not, but not only is the direct energy small, it would be very short-lived if the loop was open. You’d also get some current through the bulb if there was lighting in the area; no switch needed. Thus, you can’t call that initial phase a “circuit”, and the wires are definitely the elements that make the whole difference. You can’t use a bulb without wires.

Regarding the energy that is in the field: yes, fields store energy, but in order to make that energy work, something has to change in the system. It’s like the potential energy of a gravitational field: if the positions of the masses stay the same, there is no transfer of energy and it’s not going to be very interesting. Same with electricity. If the field changes, you have a wave. That’s the initial phase of the circuit. Once the circuit reaches a steady state, there is no field change anymore, so something else has to change to keep energy flowing: the position of electrons inside the field. Electrons receive energy through mechanical work from the field because they move within it. To keep them moving at a steady rate, you need wires again.

Tesla might have something to say on that topic. :smiley:

:slight_smile: Of course, you can do away with wires, but then, you need an alternating voltage to transfer energy, not a battery. Something needs to keep moving in there.