AlphaPhoenixes original video seems like a perfect intro to me. I think there's no harm in anthropomorphizing things which could otherwise be technically modeled. I do high speed design, including transmission paths and impedance matching as my day-job, and I found it quite enjoyable to compare my intuitions to his measurements.

I watched the AlphaPhoenix video, and I loved it. Even a little kid understands what happens there. I showed it to my wife, with zero technical background, and she understood it. I watched your video, and the only thing I can think is "this is a video for people that already know what he's saying." Your video show that you know about something, but explains nothing. It's like an answer to the prof saying "show me that you understand it", not the prof teaching something.

2:47 - your explanation sounded more like C to me. I was surprised when you said you thought it sounded like D.

Yes his terminology may not be great, but it was awesome to understand more. And the experiment itself was awesome. And the capacitor Idea basically isn’t obvious when you split the in/out cables apart. It’s basically an antenna then.

The concept of the battery “asking, knowing or updating” really bothers me. It’s like saying if I drop a rock off of a building I ask the universe what speed to let it drop at, then the rock will update me with the correct information. The hardest part of learning electricity, for me, has been filtering through people’s analogies.

His follow-up video (in his second channel) about impedance explains a lot of this with animations.

I think the misunderstanding is that AlphaPhoenix's video was meant for a general audience, and therefore used a lot of analogies rather than diving into the details of stray capacitance and inductance. You were analyzing it as someone who clearly is well versed in this field, and thus took the analogies a bit too literally.

One small correction, the voltage on the open end would be about half ie 4.5V. You allude to it saying the voltage would drop from the 9v, but put the wrong figure on the board.

Alpha Phoenix did an amazing job with this. When I watched this I immediately identified it as a transmission line problem and guessed a combination of b and c. I too forgot the impedance mismatch at the y-junction, and therefore ignored the reflection there. His technique of probing many points in the system and reconstructing a 3D map of transient flow over time is absolutely awesome, and provides a very powerful tool for understanding how transients propagate through transmission lines.

It takes me back to my degree in electrical engineering. Surprising what you forget when you don't use it any more ! Both your video and his are great videos and enjoyable to watch .

I really liked this response video, especially after watching the original one. Thx for adding some detail as to why the initial current flowing from the battery is significantly higher than you'd expect based on ohms law alone.

Hats off to AlphaPhoenix for the *_large_* effort to build the testbed, gather the data, and animate the result. Electricity is just water-in-a-pipe! Way back in college when I worked at an automotive service station, I used to drive the mechanics and parts counter clerks nuts when referencing an alternator as an electron pump. "Yeah, I need an electron pump for a 1993 Chevy C1500 pickup truck with a 5.7l engine." "Whaaaat?"

There's an appreciable difference in the level of nuance between your explaination and AlphaPhoenix's. Every edutainment creator has a delicate balance to find: complexity versus entertainment. Favor the former, and you get a lot of important details that might be lost otherwise, but you lose a sizable chunk of the audience and risk being a bore even to those who stick around. Favor the latter, get the reverse. AlphaPhoenix seems to be trying to find a balance that leans on entertainment, given this eccentric personality, almost over-the-top effort, and anthropomorphically simplified explanations of physics. Your video balances the other way, taking into account things like impedance and the fact that twisted pairs are capacitors in a fancy hat. Put simply, it makes sense that his video is missing key nuance, but for good reason. Thankfully, you're here to add that detail. I figure you already know all this; I write it out in case someone scrolls by the comments without that understanding.

I agree that the original video was fantastic in the sense that it explained electricity travelling through a wire as a wave in a completely new and out-of-the box fashion. Thank you for adding what I was missing in the video from AlphaPhoenix, which is the relation to the classic concepts of resistor, capacitor and inductance which also apply to any system of wires.

Great explanation. I always love these type of hypotheticals where people try to push physics into a sticky situation, but physics always comes out supreme with a simple and intuitive answer.

I remember studying transmission lines in Electronic Communications. Just when you thought you'd learnt about all the components, you find out that in high-frequency, a wire is no longer just a wire, but a circuit of its own with all the parallel and series inductance and capacitance, and resistance; using the dreaded Smith Chart...The system can get complex really fast, especially with interacting fields from another source.

Great explanation, but I see one problem. The open side of the circuit is fed by a splice midway along the lengths of wire. This would form a voltage divider between the battery voltage and the short, so the open end would not sit at 9v but more like 4.5

The voltage at the end of your open connection isn’t 9v. It’s going to be whatever the voltage is across the wires at the Y. This value depends on the length of the wires and where the Y is located.

this is the most insightful video on propagation e/m waves I've seen. Quite complex picture here, but it also gets almost all possible cases covered.

You put a couple voltages in the sketch; 9v at the positive battery terminal, 9v at the open end and 0v at the short. Assuming that all sections of wire are equal lengths and conductance, shouldn't the open end be 6.75V (1/4 the way down the total voltage drop) and the short at 4.5V (half way)?

The pretty similar result will happen without twisted pairs and even if the wires are quite far apart. Capacity and induction may give some additional explanation of the back and forth voltage waves, but fundamentally the behaviour is just to locality of the universe.

isn't it the same topic that Electroboom and Veritasium debated?

I was in the process of composing a comment on the AlphaPhoenix video when I happened to see YOUR response video in the corner of my eye. So, I backed out of composing my comment and decided to first watch your video in case you might have already stated my own concerns about what goes on during the switch ON period of the circuit. Well, I no longer needed to compose my comment because you stated EXACTLY what I was going to state! Like you, I have a basic understanding of electric circuits and how transmission lines behave. There are many interesting things that happen during the first few nanoseconds after the switch contacts are made. Although I agree with everything you stated in your video, I believe there is one phenomenon that both AlphaPhoenix and you might not have thought about. That is, as current flows through a metallic conductor, the temperature of the metal will increase over time. This is especially true when the conductor is thin and the current source is significant enough to heat the wire at a measurable temperature over a relatively short span of time. That might be what happens when AlphaPhoenix stated that the current flow noted on the oscilloscope trace takes some time to "settle down". As the wires heat up, their resistance increases. As their resistance increases, current draw will be lower. When the heated resistance of the wires get to a point where the current flow cannot increase any longer, the circuit becomes stable, and then it no longer looks like capacitors and inductors to the power source. It's all pure DC at that point. Then, when the switch is opened, the circuit again looks like a series of capacitors and inductors for a few nanoseconds.

I watched this same video not knowing any of this. Very interesting to hear about the perspective of someone who knew about this. Thanks

Bob, It's great to see your videos back on here! Subscribed again.

The battery as you mention has impedance, it also has initial capacitance it self, and then it has to rely on the speed of the chemical reaction to start generating current, al this takes time. If you used a high current stabilised power supply you would find the wire/reflection would take on a different pattern, adding further capacitance until the discharge current was a mear fraction of its capability would also affect the pattern change.

Thanks, I didn't watch the original video and didn't think about it much until I seen your video pop up. My first first thought was there would be some capacitance and a little bit of inductance along the wires so the open end would have a moment of current flow when the battery is connected. I expected a small spike in voltage but that's just from experience rather than electrical engineering knowledge. I'm not an electrical engineer. I would have expected some amount of a return wave from the initial spike but had no idea how that would look graphically until seeing the visualization snips from the other video. That being said, now we know (visually) why capacitors and inductors are important in noisy circuits, as well as voltage bleed ups/downs for switches :)

To be fair neither C nor D represent an accurate description of the dynamics of the system. Edit: this isn't really a criticism. I loved the video. I think it's a great way to explore the subject. He has a marvellous way of explaining things. And indeed, I've loved all his videos.

So, is this how that device can measure the distance to where the wire has been cut?.. Just applies some voltage and measures the time for the reflection from the break in the wire to come back?..

At 8min in you state that the voltage at the open cicuit ends settles to 9V. This is incorrect, as the o/c leg is tapped off part way along the wires between the battery and the s/c, so the final voltage at the o/c ends will depend on the distance of the Y tapping point along the wires, the resistance of the wires and the internal resistance of the battery. You cant neglect these resistances because without them the reflections carry on indefinitely.

You both did a great job of explaining the solution to the question!

I'm glad you responded to the video. I love both of your content.

Loved the original, loved your reaction video. Out of interest, what's going to happen if the wires are nowhere near each other? So you have a bif figure 8... a long eliptical loop of wire going right and open circuit at the far end, and a long eliptical loop going left with a short circuit at the far end.

Thank you for making video response…very informative! 👍

I appreciated the test setup. I'm familiar with wave theory, impedance and reflections hitting open vs closed terminations, so expected that result.

The reflections are definitely interesting, we see these type of things in OTDR fiberoptic testing where bulkheads, bends, and fused fiber reflect during testing especially at junctions.

I'm curious what this scenario would look like if the wires weren't twisted together (or next to eachother) and there wasn't effects caused capacitance and the like.

I think your complaint about the word "guess" is being a bit pedantic. It's really just an accessible anthropomorphism that encapsulates the fact that the steady state does not occur until everything propagates through the system. The "guess" is sloppy language, but it is not incompatible with your point -- at t=0, the newly attached transmission line behaves according to its characteristic impedance until discontinuities and terminations are encountered. So we could be colloquial and hand wavy a bit, and say the battery "guesses" that it's an infinitely long transmission line :-).

Great video. Are you doing these from a school or from home?

are the lengths and other params of the wires listed somewhere? would be interesting to use Laplace response to u(t)

I'm not a radio expert either, but have worked in power plants/ utilities. Even at 60 Hz, long transmission lines have a characteristic impedance. The actual limits to how much power we can send down a transmission line is limited in part by this impedance. Given that the voltages at each end are required to be maintained within limits, if the power input at one end is too high, we can 'pull out of synch' and that causes the generator to trip off the line. It's a complicated problem with power angles of each generator. But it's interesting that those high tension lines, with straight conductors spaced many feet apart still have capacitance and inductance per mile that is accounted for in design.

homie straight up made a video to show how smart he is to get the answer right lol

In my intuition the capacitance of the twisted pair has negligible effect at that vintage and distance - I doubt there’s any effective current as a result of capacitance between the TP; it’s just transient current inside the conductor. The circuit would behave the same if the wires were far apart

Before watching the video (and after Alpha Phoenix's video, but roughly the same comment as before): Electricity works like water pressure in pipes, but faster and without surface tension and other fluid-specific dynamics. “Information” and other quantum physics highfalutin terminology for what is essentially statistical terms for observational results of experiments are not the core mechanics happening here- everything works exactly as you'd expect electrons attracted to holes (spare orbits around atoms) and repulsed by an overabundance of other electrons to work (just like water molecules vs. air or vs. already-compressed-water).

at 7:02 you say whenever you get a change of impedance you get a reflection. when I see the wave front hit the Y, I imagine a reduced impedance (the cross section of wire is doubled downstream) and that would be a sink for the power. can you develop why there is a wave reflection back to the source here? Also isn't the internal battery resistance very significant with regard to the power (change in electron density) of the initial wave front?

In Alpha Phoenix's visualisation there was no negative reflected wave from shorted end, voltage didn't go negative. Is something wrong with his visualization or measurements?

I am reminded of the Carrington Event; just how did the telegraph work without normal power being connected?

At 08:00 you said we have a "negative wave" reflecting back. What's that supposed to mean? Thanks

I understand the capacitance and inductance of a wire pair is important, but how should the response change if the wires are "sufficiently far apart"? Is there a way to perfectly isolate the effect of one wire on another, and if so, how would that change the response of the initial propagation? This question is way above my knowledge on the topic :p

So is the behavior of this circuit just kind of a geometric accident of the fact that twisted pair wires have the negative and positive lines so close to each other? if you separated the wires would the behavior be substantially different or just slower?

Bob, What happened to your original channel (RSD academy)?

Your wrong about the 9v in the unshorted branch after stabilization. It can only be at the same voltage as the branching point wich is obviously below 9v

Then I watch to 9:00 and I found why didn't you find 4.5V at the shorted end as the resistance in both wires is approximately the same?

So happy to see this gentleman back! I was worried something terrible happened. Very good presentations.

Nice reacting to the video. But how did AlphaPhoenix make so many measurements down the line using a 2 channel oscilloscope?

How would the circuit react differently if the lines would be separated extremely far from each other such that they have very little capacitance? I guess the inrush current would simply be smaller and it would settle sooner?

while not being “boring” is definitely a factor for channels like his I think the real thing theyre balancing is accuracy vs actual learning. It’s not that if it gets too complicated/nuanced it’ll be boring and nobody will watch. It’s if it gets too complicated/nuanced the amount of people who will understand _anything_ I’m saying will be incredibly small.

Hey great to see you again Bob!

Something like C is the only thing that makes local sense. But when studying electronics alot of focus is put on steady state solutions. Essentially early on in studying these things transients (the stuff that happens before steady state) is entirely ignored.

The battery is trying it's best instantly and then fail (a bit of resistance) and go down to 99-?% and further down as heat and destruction changes things. You get around 9x3A=27W for a short time and depending on the specs, maybe smoke and a burn somewhere like a fuse. If you hurry and disconnect then it might survive and there is a fault to deal with that seems mysterious.

Good response to a very nice video. It's been a while but I really like your videos. Great to see another in my feed. My guess was the initial current would be limited by the battery resistance and then the high frequency stuff would do all that magic that's encoded in Smith charts until it reached DC. That didn't quite fit any of the given answers but I was okay with C.

I agree that the "correct" answer as expressed by Alpha Phoenix was poorly phrased. Aside from that flaw, the demonstration was pretty brilliant, however. I think it was a deliberate choice for the creator to not express the true process in technical language such as "capacitive and inductive coupling," in deference to those who know perfectly well what electricity and wires are, and nothing about capacitance and inductance.

Yes his original video was well presented. I worked out the wave periods, much like acoustics waves in open or closed pipes, but using v = 2x10^8 m/s for v and wavelength given by the fundamental standing waves etc. Anyone whom studies acoustics will know what i'm talking about. Much the same for transmission lines. These waves rapidly decay away leaving the necessary dc currents of course. I did not try estimate the decay rates because well its complicated. 😌

Really astute analysis of what’s going on in the transient case. Now, could you please go to Veritasium’s “Electricity doesn’t flow through wires” video and make a response to _thst_ that puts an end to his counterfactual nonsense?

My response to which option was correct was "kind of a bit of everything", heh What I expected: You connect the battery to the wire, the voltage will rapidly increase, up to the battery voltage. I see voltage changes as having momentum, so it will overshoot a little bit, then correct and go back down, but overshooting again, and so on until it is stable. There will be some initial current through the disconnected wires, which will stop soon after, and there will be continuous current through the connected wire. Now, my "momentum" explanation turned out to be fairly close. I didn't consider reflections, but it makes sense in hindsight. With the "momentum" explanation, you would expect an almost perfect sinusoidal graph of voltage around the battery voltage. If you consider the reflections, the actual shape can be better anticipated, but I still say I got the rough picture right.

What you mean when you say reflects? Refering only to the graph he showed, I didnt quite see a reflection, I mean a literal reflection hence the question, using the water analogy if a flow reaches a steeper incline the water will have less resistance right before the incline, as he shoes in the water examples it doesnt ripple backwards but I consider the static drop in height from the water the same as a back propagating drop in electric circuit, but I dont consider that a reflection, another example is if you skydive and you pass through a pocket of lower density air (lets go wild and say its .5 atmosphere) you go faster because the terminal velocity is faster but there is no reflection, you just went faster, in the eletrical circuit when the voltage drops isnt it the same? Isnt just the flow adjusting naturaly to the condition ahead?

i've been trying to learn about tx lines. your video confirmed that alphaphoenix's was a study of transmission lines. it's its own subject for sure. i wish he would have mentioned more about distributed capacitance and inductance, like you did, but, you can only go so far into it in 30 minutes. he did an amazing job modeling, measuring, and displaying the results. and you did an amazing job helping to explain it.

What's interesting here is that what alphaphoenix (and veritasium, i think) are sort of doing is trying to create an understanding of electricity based on the EM field properties alone, and not in a component-wise manner. which makes some sense, and is more satisfying to someone who doesnt have the component-wise understanding. the problem is that, often now people are taught about ohm's law, kirchoff, a few basics like that, and taught about resistors and capacitors and inductors and diodes and transistors, with the vast majority of examples you get being DC and low frequency. we completely miss an understanding that *does* contain all the information required to predict this. nobody told me about transmission lines. impedance is magic. RF is dark magic. AC is something you put through a rectifier and stop thinking about. this is the perspective from which you have to see the deep desire for videos like alphaphoenix is making.

Batteries think? Can we anthropomorphize electricity much more. Leading edge of the power is a wave front and best described with Impedance formulas. Study oscilloscope probes and it only gets harder.

5:31 I left the same comment in his video. There is no guess involved.

good video thanks for uploading

Fun to (1) Devise a simpler geometry to compare with actual numerical solutions to Maxwell's equations and (2) Link all with the frequency-response results from transmission line theory.

I know almost nothing about electronics, so my take may not amount to much, but what I got out of it has to do with my unintuitive confusion about quantum mechanics: specifically quantum entanglement. What struck me was the description and demonstration of the electrons physically piling up in the dead end of that split setup. It got me wondering: Here is a demonstration of classical physics. Electrons have to "go" to all parts of the setup. No mystical spooky action at a distance at all. It required "information" to be transmitted physically, and equilibria to be established, just like any other fluid system. In the dead end, excepting some jiggling in place and perhaps some 'diffusion' at the fork, electrons 'stopped' when they could go no further, and in the open end, they flowed like water molecules down stream, because they could. No weirdness. No magic. Am I all wet?

my biggest gripe with that video was that the multiple choice doesn't really make any sense, and even after watching the video I wouldn't have known which answer was supposed to be correct if he hadn't just said it was C. it's a still a really wicked setup and visualization, and the second channel followup on impedance matching was also amazing

The phrase: "The battery 'guesses'.." threw me off..

Alpha Phoenix did a fantastic job of showing the experimental results. The only "problem" was he anthropomorphised his descriptions of what happened. He said "the battery guesses" and "the wires negotiate'". They do, but just through plain physics, not intelligent decisions. But I'll give him that. It just made the explanations of what actually happened easier to understand

well done.

So glad I found (this) your newer channel! Teaching/Learning electronics can take so many forms, from funny(@ElectroBoom) , wild (@StyroPyro) or eccentric(@AlphaPhoenix).... but In terms of actual education, I always found Bob and his whiteboard the most concise and informative! Def, resubscribed! Cheers from Texas!

imagine what it must be like to take into account these reflections when designing a micro processor. its 8 reflections in just 2 wires

the kind of shit I'm watching while baked at 6:33 am

Glad I watched this instead of the original video. Thanks. UPDATE: Watched the original and it’s pretty awesome too, despite his weird choice to portray parts of the circuit as active agents that need to “decide” what to do.

Is this not reminiscent of Einsteins explanation of how a detector can detect a photon before it reaches the detector ? Some type of bow shock ahead of the particle I know it’s not but …. It’s crazy thinking everything we look at is made of particles and those particles are looking back at us.

Subscribed!

Have you seen his second-channel compainon video, where he talks about impadance-matching (kzfaq.info/get/bejne/iNFxeZaJm8mukWg.html)? What he talks about there is a different way to say the same things that you did here with the transmission line (capacitive & inductive coupling). It's still nice to hear it framed in a different way, though!

Im a litle confuses. based on what you said I thought your answer could b C but maybe my english is just not so good

You are a pretty smart man, just a little bit after the fact...

Velocity Factor? I'll be... that's very interesting.

Yeah I don't like the modern "it thinks it needs to..." approach to explanations. But I guess when you're trying to relay complex concepts in a way everyone can instantly relate to because the details stand in the way of current context, you have to break it down and lose those details in analogy. I agree with your assessment... and thought similar at the time. The other thing that came to mind (and you mentioned with 50%) was the idea that the LC coupling will slow down the propagation, making this a cool but ultimately inaccurate way to measure the "speed of electricity" in any given wire. The proximity to other conductors will play a non trivial role in this effect. I would like to see you guys hash this out "Steve Mould" style, as you're both "correct", but this addresses the shortcomings of explaining things that aren't even close to straightforward.

If you are really interested, study electrical engineering at a university. There's nothing new to the field that Apha Pheonix showed. He just made a visual for the lay person.

*Chapters* 0:00 Recap: electricity fork 5:33 My answer: capacitor interpretation

The real question. Is Turkey Point and St Lucie Plants actually interconnected? I am the reflections! 😂🧙‍♂️

I totally disagree with the original video. If you read the multiple choice options then some kind of fit the observation, but with each he adds extra like the "Current starts in one leg" then gives the answer as C in which he states the battery sends an arbitrary amount of current but its exactly the right amount as predicted by many and then goes on to say about the information going back to the battery and telling it what to do, but its doing what it needs to already and has all the information it needs to do so and the reflected wave just changes what it is that it needs to do..... I found it a super interesting and fun experiment but its presented like a school science teacher giving a lesson but to me its likely to just cause more confusion like when teachers start talking about the size of the singularity in the center of a black hole.... I think its often better to just say I don't know for sure but this is my assumption because of ....... and leave it open to be further probed.

There exist photons which i call elektons that are always propagating at the speed of light in every direction along (hugging) the surface of all metal objects, for ever. The speed of the elektons will depend on whether the say wire is enameled or insulated (speed is say 2c/3) or bare (ie in air)(speed is 1c/1). The numbers (ie the saturation density) of elektons depends on the metal concerned. Elektons give what u call electricity, what i call elekticity. No electrons are involved in elekticity. On a metal object (eg a wire) the nett elekticity is zero, unless we connect a say battery (giving a circuit) or at least one terminal of a battery (giving a dead end). If we connect a terminal to a wire then the terminal will pump elektons onto the wire, or it will rob elektons off the wire. Likewize for 2 terminals connected to a circuit. Elektons on a wire do a u-turn at the end if a dead end. Actually, the elektons go straight ahead, the surface duz the u-turn. Similarly elektons do a u-turn at changes along a wire (eg change of alignment shape size nature etc). When a terminal is connected to a wire, the saturation of elektons on the surface (initial density & then transient densities) eventually settles down to a (final) density depending on the metal concerned & depending on the (say voltage of the) terminal. That is the reality. Anyhow, the wires will have waves & pulses of elektons propagating all over. Until the flows stabilize.

I taught myself electronics in 2015, and I predicted the outcome of the experiment correctly, but I really wouldn't know where to begin with an explanation. I just don't think that a charge density, and electron mobility, boundary condition explanation is something that would be useful to anyone, even if it let me make an accurate prediction internally. Your approach really clarified how to communicate the concepts. 6:27 highlighting the parasitics as the active components, makes for a much more manageable approach, thank you.

5:38 i guessed D too

your schematic is incorrect. the two branches are in a parallel, not a serial configuration..

Electricity's not real.

Time Domain Reflectometry

I'd be much happier if you would not state that the battery and the current 'realise' things or take action based on events. They don't, they are not sentinent thinking entities. It won't help students to have to try to work out what a battery is 'thinking' if were an intelligent entity it could think anything!

I watch to 6:20 and notice the sketch is wrong.