I’m so glad this video exists. I use to completely not even understand how electricity worked, and now I still don’t.

Well well well, stepping into my territory, eh?! I shall make a video about this!!

when i lived on land like a normal person, i never thought about this stuff. now that i live on a sailboat, i'm obsessed with how absolutely "normal" things work and electricity is my favorite topic because it's so MYSTERIOUS!!! i loved this video :D

I gave up learning. I burned out. But this channel has reignited my joy and love I forgot in my youth and curiosity I had for the World. Thank you sincerely Sir.

EE here; I think most of this info is technically correct, but potentially misleading in some areas. For one, while it's true that energy is transferred in the space around a conductor, as opposed to through the conductor, the *vast* majority of that transfer is taking place *extremely* close to the conductor (we're talking millimeters, typically), due to both the magnetic and electric field strengths decreasing exponentially with distance from the conductor. So in reality, the energy being transferred actually decreases superexponentially with distance from the conductor. Now, in power lines, the ground is still a concern because it's a very long conductor, carrying very high voltage, at very high currents; it's a somewhat extreme case. Yet, even though the cable is *miles* long, we only need to separate it from the ground by tens of meters to significantly reduce losses over that long distance. Furthermore, the ground is only a problem because power lines are AC. If they were DC, you could lay the cable right on the ground, and you wouldn't get any significant energy loss. Edit: see below, the dropoff is not actually superexponential, but the general idea that energy transfer is greater closer to the conductor is still accurate. For two, the analogy of electron flow being like water through a tube is actually still accurate in the case of the undersea transmission line. The metal rings around the cable cause a change in electrical impedance for that section of the cable. In the case of water in a tube, this would be analogous to having an air bubble trapped in your tube. As a pressure wave travels through the water, it will suddenly hit this air pocket, which is far more compressible than the water (i.e. has a different impedance), which will cause the waveform to distort in precisely the same manner as the electric wave does in the cable. Some energy will pass through the bubble, creating your distorted (attenuated) waveform, and the rest of the energy will actually become a wave reflected back in the other direction. This is precisely what's causing the distortions in the undersea transmission line. There's a bunch of reflected waves bounding back and forth between all the iron rings that stretch and distort the original signal. (for the real electrical nerds, check out "time domain reflectometry", which uses this principle to precisely detect where a fault exists on a power line) Third; yes, energy transfer from the switch to the bulb will occur in 1/c time (by the way, I think you could clarify this by representing it as d/c time, where d is distance from the switch to the bulb. You never really state where the 1 comes from in that equation (at first I thought you were implying it was a constant value, unrelated to this distance)). And yes, you do clarify that it will only be a fraction of the steady state energy. But I think you should stress that this would be an *extremely* small portion of that steady state energy. The initial energy that the bulb receives will only be due to the capacitive and magnetic coupling between the two long portions of the conductor. And in the case of wire separated by 1 meter, both the capacitive and magnetic coupling would be practically zero. This again is due in part to the exponentially decaying electrical and magnetic field strengths with distance from the conductor, as well as the poor electric and magnetic permiativity of the dielectric (air) between the conductors. Fourth; addressing your question about "why is energy transferred during one half cycle, but not returned back to the plant in the other half of the cycle", I think your physical demonstration actually explains that perfectly. No matter which end of the chain you pull, there's something down the line offering resistance to the motion of the chain. Heck, you even get friction between the chain and the tube, which is like resistance in electrical conductors. However, if you attached a sort of clock spring to your wheel (such that the spring always worked to return the wheel to its at-rest position), you would indeed see some energy returned to the power plant (you) on the second half of the cycle. This is analogous to powering a capacitive load with AC.

I teach physics at the University of California, San Diego, including this very topic. Within an hour of watching this, I set up the experiment, and got the result. I have photographs of the experimental setup, and of the oscilloscope traces. I discussed the results at length with a physics professor friend, and we agree on the explanation. In fact, the load gets (nearly) the full voltage (almost) immediately; there is no (visible) ramp-up time, nor delay through the long wires (delay < 10 ns). This is fully consistent with transmission line theory that is well established for about a century. Dr. Muller's Veritasium series is great, but in this case, there are several claims that are incorrect, or at least misleading. There are many subtleties, and I cannot do them justice in a comment. I would enjoy talking with Dr. Muller to clear these up. For reference, I have a BS in Electrical Engineering, a PhD in physics, and I am author of "Quirky Quantum Concepts", an upper-division/graduate quantum mechanics text supplement. This is my first KZfaq comment ever. Update: I love the Veritasium series, and I have learned a lot from it. To respond to some replies: I chose the simplest case, which I think illustrates the point that power can reach the load without going the whole length of the "wings." The analysis link below the video covers the more-complicated case. My "wings" are 50' hardware store extension cords. My propagation test confirms that coiling them doesn't matter, as expected. My analysis is fully transient, and the circuit transits to steady-state DC over time. Resistance can safely be approximated as zero, but inductance and capacitance cannot, as expected by theory. My load is 270 ohm, roughly the on-resistance of a 50 W incandescent bulb. The characteristic impedance Z ~53 ohm, which is substantially less than the load; that's what's needed for the simple case of near full response nearly immediately (the load is _not_ matched to Z). In this case, the wing capacitance dominates the behavior. Consolidating my previous reply: Examples of subtleties: Do two electrons repel each other? (a) Most people would say yes, and I agree. But one could argue (b) No, one electron creates an electric field, and that field pushes on the other electron. This is also correct; it's slightly more detailed, and from a somewhat different viewpoint, but (a) is still correct, as well. But (c) In calculating the force of (b), we use only the E-field from one electron, even though we know both produce E-fields. To use the full E-field, we have to compute force with the Maxwell stress tensor; this is also correct. There are multiple correct views one can take. The video's chain analogy is very good, and correct. Separately, a few replies have hit on the most-direct (IMO) explanation: the capacitance in the wires provides an immediate, physically short path for the electricity to reach the load. The path of current changes over time. Your gut might tell you that the capacitance is too small, but a quantitative transient analysis using standard circuit theory matches the experiment. Special Relativity still stands. More subtleties: characteristic impedance, etc. I do similar demonstrations in class, so I happen to have all the equipment and experience ready to go.

Finally!! I've been looking for such a video for a long time. Clear and well presented, thank you!

so.. in summary - it's the making of the connection, from your appliance to the power plant, that then causes an energy field around the wire itself (near instantaneously) that causes the device to turn on. This actually makes far more sense, basically once connected the wire is 'live' .. there is no 'flow' back and forth, so to speak, the dissipation of energy around the wire and either end is the source of the electricity. (something like that). This also agrees with my understanding of EMI (electro magnetic interference) from electronics (disrupting things like wifi signals) from working in tech. Thanks for the video, well explained as always!

I feel like a baby who just realized mom and dad don’t really disappear during peek-a-boo

After watching this video I can confidently say I understand less about how electricity works than I did before.

Watched this and it blew my mind, in all my studies they talked a lot about the flow of electricity but not the flow of energy. This just made so much more sense then electrons rushing around a cable.

Most intuitive explanation I've heard: Put down 3 coins next to each other, barely touching edge on edge, and firmly hold the 2nd (middle) one down with your finger. Smash the 1st one into the 2nd. The 3nd one will bounce away. This is how force is transferred without any noticeable movement. Same with electrons, but the electromagnetic fields are doing all the work.

And here I thought all vectors were pointing.

I'm 66 years old. As a child, we lived near large transmission lines in a rural area of CA. They passed over one of our pastures. We had a small water pump shed near the base of one of the towers. I "helped" my dad bury the power wires to the pump shed, 400 ft. from our barn/shop when he was installing a new pump. My dad used pipe strapping tape to mount some fluorescent tubes inside and outside of the shed. Everynight the lights were always on and I asked him why. He took me out to the shed, and asked me if I felt anyything... I realized that the hairs on my arms felt tingly, and I felt something in my ears. He explained about how such high voltage cables as above "induce" a magnetic field way around the big cables, that's what gives me the feelings, and what makes the tubes glow like they were wired to something. That had to have been 1960 /61- as I had just started 1st grade. He drew some sketches to show how "he thought" it worked. He gave me a basic electricity book and quizzed me every once in awhile. His sketches looked just like your graphics. I guess my dad WAS a lot smarter when I was younger. LOL

Very good visuals in explaining wave energy (Electrical and Magnetic).

love all your videos, because it challenges how we think about things and reminds me of basic assumptions on models we make, may not always apply. The only real problem (as an electrical engineer) that I have with this, is you show a DC battery and then show a light bulb being lit and continuing to be lit (caveat around that if we assume the bulb is so good as to be lit as soon as ANY current flows, in which case all the EMF and solar radiation from even the sun would be lighting it before you even turned on the switch..wink). You do bounce back and forth between DC and AC and the overall fundamentals of everything are awesome and great to explain to the layman, but even if you had a perfect bulb to detect the 1/Cs transmission and produce visible light response, it would quickly decay away and not actively light the bulb from the DC power transmission until a full second later. It seems a little misleading to show you flipping a switch, having the bulb turn on 1/Cs later, and STAY LIT on your finale... :P

Of course I find this video now… around 6 months ago I got into a small debate with my electrical engineering professor over a topic very similar to this. Everyone in the class seemed to be on the professors side which I guess makes sense but then the following week our professor walks into class and tells me he thought about what I was asking and had looked into it. He walked up to the board and showed some of the similar stuff you did in this video and proclaimed I had actually been correct and my original question that countered his previous discussion he admitted to the class he was in fact wrong. This was the first time in my life I had such a crystallized idea of what someone that was truly intelligent acted like. He wasn’t upset, frustrated or hurt that his initial statement was wrong because he didn’t care about being right, he cared about the truth. I know it sounds corny to say seeing someone look for confirmation instead of affirmation changed my outlook on life but it really did. Never before had I seen some so openly question their very own view and search for the truth rather than search for what backs up their view or idea. Great video, as always

The fundamental law of physics: electricity disappear if you stop paying bills.

WOW, as a student major in physics, that is still amazing to me.

I love this video. It answers many questions about magnetism. My comment is: When you cut across a conductor that has a black and white conductor and is conducting both fields, and create a short circuit, the power is interrupted within both pathways with a dramatic display of energy. My conclusion is: The two fields are not seperate entities but are one emmanation. It would be awesome to see another video that explains the short circuit and the interruption.

WOW! I'm 80 years old. Started learning electronics in the Army in 1959. We were taught the "Right Hand Rule" in the study of inductors and transformers. Although we knew about the magnetic field around conductors we never applied that knowledge like this. Thank you for teaching an old man a new trick.

but wait.. how can that be possible? what if someone cut the wire at the end and then at the same time you turn it on? does it still turn on instantly, but then "realises" 1 second later that the wire got cut and turns off again? I guess from your perspective, you would be turning it on first, and then from your frame of reference you would PERCEIVE the other person cutting the wire only 1 second later, despite them doing it a second earlier from their frame of reference.. edit: but what about signal reflections? what are they then? what the heck was I dealing with with ADSL ports having the signal reflected back to the first wall socket from the disconnected wire leading to the 2nd wall socket? and why do RAM traces on motherboards suffer from reflection?

Magnetism, has always fascinated me, even as a small child. I believe that there is much we do not yet understand. That there is a huge potential of amazing opportunities, in the study of Magnetism, that will prove to be, unbelievably astounding, in years to come! Thanks for your insight! Tesla would be pleased!

Had I thought about it more than a half second, I would have gotten it right, but for the wrong reason. 😂 I answered D. None of the above, believing the light to come on nearly instantaneously, but C. 1/c IS nearly instantaneously. I, too, was taught(and very much under the impression) that it was the movement of the electrons that "powered" the device, so that it doesn't matter how many you have stacked in line, the moment you push/pull the first, the movement travelled through each one instantaneously. I'm glad that I now know how electricity is actually transferred! Thank you!

I'm an electrician from the UK. This theory can be proven by holding a florescent tube near a power line. It will glow. My family didn't believe me so I showed them. So glad you explained this in a way they understands fully. Thankyou. Very clever.

"Now that you understand how electrical energy flows..." Bold assumption, sir! I'm still wrapping my head around this lol

Excellent explanation. Thank you, Sir.

After having done my masters in Electronics and Communication, from NIT Rourkela,India. Why did I start thinking exactly what is explained in this video.....!! I am glad that this video exists and recommended to me by KZfaq. Thank you..!!

I am a lowly aircraft electrical technician and mechanic. But from troubleshooting aircraft systems over the years, a fuzzy picture started to form in my head almost exactly like what you illustrated. And I've used that image to do mental checks in my head against where power is going, and if my diagnostics are correct or I have my test equipment in the wrong place. This video completed the puzzle in my head, and I think a lot of people in the blue collar world who work with electrical systems every day without ever defining the knowledge they've learned from it will appreciate seeing this video.

This video: "Forget everything you know about electricity." Me: "Way ahead of you, as I already know nothing."

I have a question @Veritasium, It may be a dumb one since I am pretty confused :) 

 In your case where the light and battery are positioned in the middle of `a` sides of the rectangle where the `b` sides represent the poles. Does this mean that if you would put the battery and the light in the middle of the `b` sides would it take the light 2 seconds to turn on ? since the energy has to propagate 600tkm ?

The fact that people disagreed with this when we've all known how the Capacitance of Capacitors can be increased by bringing their electrodes closer together is wild to me.

Honestly, the analysis from the professors made a lot more sense to me than the video just from a small clarification that I didn't catch from this with one watch, and had left me very confused. The energy most are generally used to seeing from a long, wired connection is from the "transmission line" current, but the energy being talked about here is from "antenna current," and the two modes of transfer, along with major differences in voltage that actually reaches the bulb by either type, felt like important info to leave out. The implication I got from the original video was that the length of the conductor did not matter at all for this model, but the reality was just that the 1m distance in the math, and specification of "any" current, hid the conflicting nature of two modes. So, from my corrected understanding: The "transmission line" current *would* take one second to reach the bulb, through electron to electron EM field interactions in the wire, it's just that the "antenna" current can travel there first, because of a lack of shielding, and the misconception/lie here isn't so much a misconception/lie, but a lack of information on additional modes of energy transfer. It felt like this video was more focused on becoming a popular, trick question via omitting information, rather than informing people on new or misleading information, which is not something I would/could say about any other Veritasium videos I can recall, and I do not like to say.

I’ve been an electronic technician since the 90’s and I remember one of my electronics instructors explaining this to us and it still blows my mind all these years later. Fascinating video, thank you for posting.

Mind blowing !! Thank you ! I am so inspired by you that I subscribed to Brilliant !

Super interesting. Thx for making this video. Few serious questions do arrise tho. I have ideas on the answers but I want confirmation or just the answer. If electrons move through fields of energy, why even use the wires to conduct the energy ? Is it to guide the energy on an exact path from source to energy user? Question numba two. Why do these fields of energy not shock or seriously effect us? Energy usually only conducts through us, when we touch the copper or steel in the wire. Is this cause theres a more dense or accumulated build up of energy in the wire comparered to the sosce around? Hopefully sm answers these questions, cheerio 🥂

The part about AC was mindblowing. The Poynting vector is S = E x B but if both E and B are reversed, then S = (-E) x (-B) so the energy flow stays the same!

My grandmother lived on a very remote and isolated island in Norway. When they first got electricity, they had one lightbulb connection hanging from the ceiling in the best living-room (it was only used when having fine visitors). The thing was that when the electrician first lay out the cables, they had no bulb to put in the socket. Also the electricity was not yet connected to the house but would be soon. So each night they put a bucket under the empty socket just in case the electricity would be connected while they was sleeping. Not to spill anything on the floor.

Great video... I would add that for power lines it is important to understand that the wires are used as a waveguide to constrain where the EM flows. Unlike RF, which is high frequency, low density energy we allow that energy to flow through the air, without wave guides ( wireless )... I think it's important to understand the wires are 'waveguides' for power frequencies... similar to how roads and side rails are used to govern car traffic. Larry Durante, PhD, EE

This was so cool. I didn't get the answer until the battery / light demonstration about halfway through the video.

I really like how you post a poll first and then post the video with in-depth explanation later, keep at it. :D

This actually raises more questions than it answers.

Hey @veritasium love your videos been binging them lately. this is one of my favorites. do you think it is possible to conduct this field of energy without a wire?

I've known about this for a while however you Sir have just explained it in a way that I can make sense of. Thank you.

I know you predicted pushback, and with good reason, so here it is. I’m not saying this video is wrong, but at best, it’s incomplete. First off, the fields can’t intrinsically be separated from the flow of charges as if the electron drift isn’t significant. For the magnetic fields to permeate free space in the first place, the charges must undergo acceleration to create them, and if you cut off the switch, the fields would collapse without the current. If I turned on a fan next to a piece of paper and the paper flew away, would it be accurate to say that the air alone did the deed? Sure, the energy that moved the paper was transferred to it by the air, but neglecting that the fan moved the air in the first place would be a glaring omission. It’s also essential to remember that the Poynting vector itself is DERIVED from the continuity equation (local conservation of charge), and what it represents is the interplay between the energy transfer among the fields and the movement of the charges that generate them. In other words, fields don’t carry energy on their own without the movement of charge. Also, the vast majority of energy transfer in the fields happens extremely close to the wires, and the graphic that you’ve given of these fields taking such wild departures away from the circuit ignores the infinitesimal magnitude by which this happens. With regards to your experiment, the following should be noted. Yes, there would be some current flow instantly with the closing of the switch, but only because the electric field in the conducting wire has had time to reach equilibrium along its length. If instead of a switch, you connected the wires to the leads of the battery directly, the propagation of the electric field along the circuit would occur at a speed less than that of light in free space. Lastly, I challenge you to explain the energy release from the actual light bulb that doesn’t involve electrons flowing through the filament. Also, I posted the following as a reply further on in this thread, but I'm putting it here because it's important. The power (energy per time) that a circuit puts out is always IV (current times voltage). This relation makes no reference to fields of any sort. Now, it is absolutely true that the electric and magnetic fields carry the energy - the current does not - but when one takes the spatial integration over the Poynting vector, it always reproduces the power law P=IV. The fields carry the energy, but the current generates it. You can change those fields in a million different ways and the circuit will behave the same. For example, wrapping the wires in a grounded sheet of aluminum foil creates shielding, which is how high transmission data cables such as CAT6 or COAX reduce noise and capacitance between wires. You could say that they contain the electric fields within the space of the insulation. You could also coil the wires into an electromagnet. However you reconfigure the fields themselves, the fact is that the overall power dissipation of a circuit depends on the current, not on the field strength, and to trivialize this fact by focusing on how the energy is carried is confusing and misleading. As with my earlier analogy to a fan blowing air, the energy may be carried away by the air, but the amount of that energy depends solely on the power output of the fan. Ultimately this video has some good information, but it is also extremely misleading, and I caution people to take any claims that “they way you understand things is false” with a grain of salt. Usually, there’s more nuance than that, and as something of a cynic myself, I think it’s often a form of clickbait. I encourage interested viewers to look elsewhere for the full picture of electrodynamics in all its beauty.

At the end of a very intese physics course and right after the exams, our teacher ended it by telling us that everything we had just learned about the flow of energy in an electric system was most likely wrong and mentioned something about energy not passing through the cables. Now I finally know what he meant. Thank you 😅🙇

OMG! BEST EXPLANATION EVER! I was an A+ student in only one class in my life, electronics! I always found manipulating and controlling electricity in various ways, exciting, appealing, easy and yet still kind of mysterious. I accepted the explanation that "electricity" was defined as "movement of electrons from the outer shell of one atom to another" but it never made sense to me how they were consumed, or how alternating current actually worked. All that nonsense they teach about alternating current, I always said was "explained what was going on" but not the "why, and how". I truly thought no one alive actually understood electricity or at the very least, alternating current... Man was I wrong, and I'm so thankful for the education!

0:37 maybe 2 seconds or 1/c seconds Because the wire is as long as light travels in one second but it is a two way trip so 2 seconds. Also, you said the wire is 1 meter from the light bulb and I learned in “no one has measured the speed of light” by vertasium 1/c = 1 meter so, 1/c is another possibility. By Liam Bello, 8 years old

Derek is somewhat right about the time being roughly 1m/c for the bulb to light up but only because the parameters of the problem were picked to be tricky (sometimes fun and educative). Unfortunately Derek doesn't go into details in the video and only says that the bulb "won't receive the entire voltage of the battery immediately". This may mislead you into thinking that the signal speed in an electric circuit depends not on the length of wires but on the air distance to the switch, which is wrong. The signal speed in wires is roughly 50-95% of the speed of light and most often is what dictates how long it takes for something to turn on in most circuits. This is why, for example, matching copper trace lengths in PCBs is often important. Or why high frequency trading companies care about their internet cable lengths. HOWEVER, often in circuits there's significant wireless EM radiation, intentional (radio, wifi, microwave) or unintentional (reduced with EM shielding). Turns out that in Derek's circuit one side of the wire initially acts roughly like an antenna while the other acts like a receiver and the power transmitted could be enough to light up an LED bulb. At 100m it wouldn't.

I am a third year Physics uni student and I can onfindently say that you have managed to explain the poynting vector better than any of my professors ever have...

Very interesting. You brought me back to my years at the ninth grade at high school when I asked myself this question and made some reasonable guesses. I wish I had a teacher like you. By strange coincidence on my entry exams to Moscow University I had to explain electromagnetic induction and during rather detailed examination a professor asked me about behavior of electrons in a conductor. I presented my "reasonable guesses". Those days exams were blind - they didn't know anything about me. But the professor smiled: "You are not from a big city?" I said, "No, I'm from Ukrainian provincial town". "Did you read a book by Zhdanov recommended as an extra material for AP physics?" I said, "No, there were no such a book in our library". He smiled again: "So you figure out yourself". I got A and was accepted.

Well this video answered some questions of mine, but raised many more. One of being that if the battery and bulb were kept far then the field should take much more time? right? So if it were kept 1 lightsecond far then will the time between it lighting and key closing will be 1 sec?

"What you were taught about electricity is wrong" Me (an electrical engineer): "I sure hope not"

Amazing explaination of such a simple phenomena which textbooks do a deservice , kudus to that amazing idea of poynting vector.

brilliant. as always. thank you for sharing! :)

The central issue here is the muddy definition of the bulb being "on". It obscures the fact that there are two separate events in terms of current in this scenario. 1) After 3.3 nanoseconds, the light bulb will experience a very tiny electrical signal. This is true even if you cut the wires, and has more to do with antennae than circuits. (Hell, you might as well say the light bulb will turn on *before* you close the circuit due to the ambient radio signals) 2) After 1 second, the light bulb will experience the full voltage of the battery like it would in a "normal" circuit. The energy does travel along the outside of the wire, but the vast majority of it stays very close to the surface of the wire. Thus, when talking about energy propagating in circuits in any real sense, it does need to travel the entire length of the wire.

I think one of the most difficult things about the Poynting vector is to visualise the cross product in your mind. That video with all fields represented in space is extremely helpful and should be shown in EM courses.

There seem to be two distinct claims here: 1. the energy from power plants to homes is carried by EM field around wires, which I find clear. 2. But, if a bulb is 1m from a battery and the wires are much longer, the time for the switch signal to reach the bulb depends on the battery-bulb distance only and takes just (1 meter/c) seconds, irrespectively to wires' length. Wires are necessary (putting a bulb near a battery does not light it up without wires); however, their length seem irrelevant for the system's response. This seems to give a superluminal signal speed for any wire longer than 1 meter?

Great video! Thank you.

I think the best part of this video isn't just the information it presents, but also the conversation it sparks in the comments! People asking questions, people trying to understand what's being said, and even people providing counter-arguments in certain scenarios where what Derek explains doesn't seem to match up. I think having civil discussions helps a ton, thanks Derek + the Veritasium community! This video and the comment section is genuinely interesting to go through

Considering how long ago we learned to harness electricity and create electrical circuits and how much misconception surrounds it, makes me wonder about other things we've misunderstood yet utilized nonetheless.

I have some doubts. Despote having a phd in physics I am not an expert (anymore). Regarding the set-up with the light bulp next to your battery and your explanation energy is flowing "the short distance through the air": Why the light bulp does not light up when you create two seperate circuits even when you ensure electric and magnetic flieds are present in the circuit connected to the battery? And would the light bulp have a delay if you place bulp and battery far away from each other?

Electrons transfer potential like shaking a hose at one end. Electromagnetic potential is harnessed by electromagnetic devices that are designed to work with the system its attached to. In alternating current power is developed by alternating magnetic fields designed to accomodate the frequency of the power source. Electron drift is what causes conductors to eventually wear out.

I have so many questions: - If the energy moves through the fields, how does it light a bulb? What takes on the energy? - People in the comments talk about shielding the bulb from EM fields. How does it work then? I need pictures. - how do computers work, transistors, if it's not the current that moves the energy? Give us more of this!

"Looks like we're getting a new Veritasium video." "Why? Because he posted a poll on KZfaq?" "No, I saw him standing on that hill again."

This is such a good channel. Im obsessed 😍

EXCELLENT WORK!

What a perfect name Poynting had so that his vector points in the direction of energy flow! Reminds me of how the Schwarzschild radius for a black hole was calculated by a physicist whose last name means "black shield" in German.

I have a degree in Mech Engr and my Physics E&M class was the only class where I was like “yeah I just don’t get this”. Sometimes I’ll wonder though if it really was that bad. This video just reminded me that yes, yes it was that bad.

Tesla understood all this and thats why he is one of the greatest investors in the history of electric science

This is an elaborate explanation of what's going on, but nobody fully understands why and how. I suppose there is background knowledge at an informational level beyond the reach of the human rational mind. But the main thing is: it works!

Oh yes, please do an experiment in the Mojave desert! Also let's check a few more variations: 1. arrange the circuit in a circle - that way the shortest path through space would be the diameter 2. enclose stuff in a Faraday cage to block the fields from taking a shortcut and see if it lengthens the time to light up the bulb

Still having one doubt: I understand that energy doesn't need to travel through the whole circuit, but how does the light bulb know it's a closed circuit when you flip the switch? Let's say the wire is cut off somewhere very far away from the switch and the light bulb, information should still take time to travel instead of instantaneous. Unless it will work even if it's not a closed circuit, but this doesn't make sense either. It's like I can just flip a switch near a light bulb and it will magically work without a closed circuit. I know it may work without a closed circuit like a transformer, but this setup is not like that at all. Also, mentioned by Rick K in the comments: If this is true, then why don't we use that effect for "faster than light" data transfer? If the light bulb "reacts" to the switch almost instantly, that would mean that the "information" transferred with the flip of the switch is also transmitted instantly.

In telecommunication electronics engineering we call it skin depth of a wire at different frequencies. For 50/ 60Hz frequency which is used for electricity generally the skin depth is more. Higher you go it decreases therefore higher the frequency is, lower is the skin depth so electrons flow on surface and the Copper material towards the center of the wire goes wasted that is why for higher frequency thick copper wires are useless therefore thin wires are used and diameter of the wire is kept slightly larger than skin depth of the wire at that higher frequency. Nikola Tesla emphasized upon use of higher frequencies power transmission which provide high voltages but low current, less material cost and economical where as 50/60 Hz power systems require more copper have high current low voltage transmission and very costly but obviously Edison was more resourceful than poor but genius Tesla.

❤ he is the teacher that every student needs

I see many engineers talking, and as non-engineer, I got more confused Hope you can do a follow-up video! Some questions I hope I can learn more about: 1. The video seems to suggest that to transfer energy, just setting up a simple wire to set up the electrical field is sufficient. So how does resistance, voltage and the entire electrical engineering degree come into the picture? 2. With so many wires around the world, do these energy fields interfere / cancel each other? I might have some misconceptions, so do advise!

It's great to see the Poynting flow argument reaching such a large audience! I always cover this in my college E&M classes. But I have to say that the claim that the light bulb turns on right away is pretty misleading. Consider the case where the circuit is actually open -- somebody cut the wire 300km away. By causality, the light bulb's behavior is identical in both cases (closed and open circuit) for t

This is giving me flashbacks to a physics course in uni that helped me decide to drop engineering for compsci.

Absolutely love and appreciate this video

As an electrical Engineer who works in a transmission company, this video explain the basics well

Hello Derek, a physics professor here. I love your videos and I subscribe to your channel - in all honestly, I consider it the best example of public communication of physics and science I have ever met - I am not exaggerating. I actually used some of your videos when teaching to my students. However, you did not convince me with this one - not that I love you any less for this. I have similar objections to some that have been made by others here. The explanations of the fields, and the Poynting vector are gorgeous and very instructive, by the way. But I have tried to explicitly calculate the flux of the Poynting vector on the bulb, and I find it to be quantitatively a small effect (quickly dropping with distance of the bulb). Yes, there is *some* disturbance at the bulb, but I think it is a bit misleading to just say that it "turns on". I suggest to have this checked by other people - I would be very curious to see a follow-up on this. You are actually tempting me to try this out in my own lab. Anyway, even if it turned out you had slipped on this one, that does not change my opinion about your work. Physics is non-trivial, and what really matters is to have the right scientific approach to problems, not to never ever make a mistake (even Galileo did) - eventually things sort themselves out if you follow the right track.

Almost everything that uses electricity in your house uses electricity that is converted from AC to DC. Light bulbs, door bells, toasters, ovens and stoves, fans and maybe a couple other simple things can use AC current, but not you TV, Stereo and anything else that functions at a more complex level uses DC.

So question if the line is cut in one point how long does it take for the light to turn off, I don’t see how it could be faster than the speed of light as a that is the fastest information can travel. And a follow up to that is if the switch it turned off and the path is broken at the same second the light should still turn on immediately right because the information that the path is closed was not received. But the path is broken so how is there any current flow?

I am a Master Electrician for 30 years and we more or less where taught power was sent the tough the "skin" of a wire. Fact is many terms used are made simple so people can grasp it in real life situations. Wires clearly have a magnetic field around them or am amp probe would not work. Also working with high voltage cable there are bleeders around the cable like coax cable to discharge stray voltage or with cable wire shield it from stray voltage. I have a collection of old electrical code and theory books back to 1897 that hint at forces they did not really understand but they were spot on in almost all theory even in 1897. The books were made simple to explain wires like plumbing pipes, size vs pressure and this was good enough to have a practical understanding to size wires correct. I see this a lot like gravity when it is calculated as a force that pulls or attracts mass. That is not how it works but the math is correct even if the understanding is dead wrong. Mass bends the grid of space so objects are traveling straight on the grid but the grid is distorted.

That's a great video about power transmission! I remember being surprised by that in the university. I really don't like the 1/c answer, though. While it's technically true that there will be some voltage on the lightbulb after 1/c simply because the electromagnetic fields generated around the wire will reach it, but it has nothing to do with them being connected by wires. In the same way, you can say that turning on this battery will "turn on" every single lightbulb on the planet. This is also technically true, because there will be some field generated by the battery in the entire space, and it will induce some voltage everywhere. Although its value will be negligibly small, as the magnitude of fields around the wire quickly drop with the distance from it. Only after 1 second, the proper connection through the electromagnetic mode of the wire will be established. If you replace the wire with an ideal coaxial cable (which doesn't let any EM fields outside the inner space between the two conductors), the answer will always be 1 second, as there's no leakage and thus no way for the lightbulb to receive the EM energy from outside the incoming cable.

When i got taught about electricity in university back in 1984, the lecturer said electrons flow through the wire and they leave a hole. The hole effectively travels the opposite direction to the electrons. It still doesn't seem to make sense.

Still nice to know that ohms law and its ac derivatives "work" though, how resitivity and cross-sectional area of conductors play a part in the ability to transmit/pass current (the flow of electrons) which is requred to perform work. There's also the confusion of comparing sending/modulating energy for communications purposes distorting dots and dashes (interrupted dc back then) vs sending energy for "work" purposes. The concept of free electrons drifting between atoms under the influence of EMF is a pretty good fundamental model to have, Newton's cradle is often used as a visual prop/way of thinking about it.. Transformers (and capacitors, even optocouplers, acoustic couplers etc) are "breaks" in the circuit for the electrons, but not the energy, as it's transformed from one type to another and back again.

This is kinda inbeliveable and really hard to imagine. I really need more examples. Like, why this energy flows through us freely, but strike us if we touch the circuit. And how exactly it converts into light or heat.

With such a long wire, how do the fields "know" where to go? How is it able to transmit energy immediately, but a disconnected lightbulb another meter away wouldn't power on? (or maybe it would?) In fact, how does current "know" to start flowing when the circuit is complete? Or what would happen if you cut the wire at one of the tips? Would the field instantly start receeding everywhere? 1/c seconds to turn off?

The conductors are connected to the battery and fully charged, so when the switch is closed electrons don't have to flow 300,000 kms. Connect positive and negative terminals simultaneously on the battery and see how long it takes for the bulb to light. The conductors are already full so the electrons don't need to travel. Turn the faucet on for your garden hose with an empty hose and wait for the water when the sprayer is opened then try it with a full hose.

Another important thing worth clarifying is that prior to the switch being closed, we have to assume that the system is in a steady state with a buildup of opposite charges on either terminal of the switch (if it wasn't in a steady state, then the light would already be on). When the switch is closed, current starts flowing (which sets up the magnetic field and radiates energy as discussed in the video), but it starts flowing at the switch and not at the battery. The battery doesn't "know" that the switch has been closed until the Poynting vectors from the switch reach the battery. So it's really the distance between the switch and the bulb that determines when the bulb first experiences any current, and not the distance between the battery and the bulb.

I remember day 1 of EE being like, "so we're going to learn how to do circuits over the next couple of semesters and when you take EM fields you'll learn why all of circuits is kinda wrong." Turns out he wasn't just messing with us.

As an electrician who went through a 4 year Apprenticeship, we were always told electricity ran through the wire ..... smh... they need to teach this in schools

It would be nice to know on which book is written the first 3 minutes of the video. How in the world a problem to describe how a bulb works get confused on how energy travels along wires? At the end of the day the question still remains unanswered.

As a tradesperson who has created and installed many home wiring circuits, wired up car stereos, installed lights and even built circuit boards; you have shattered the sense of pride and accomplishment in what I've done by pointing out I didn't REALLY know what I was doing. I'm going out to rub two sticks together in order to claw back some small semblence of human ingenuity.

I really like how you have started almost teasing us with the community posts and awesome follow up videos, please keep at it.

The energy is transmitted through the electric and magnetic fields around the wire. Why does a wire get hot if you "pass too much current through it" if the energy is being transmitted outside of the wire? Does the wire's resistance cause it to act as a roadblock to the fields around the wire and they end up imparting energy into the wire itself?

Nice, Explaination man.

This was a GREAT explanation of circuits and electromagnetic energy. The one thing that could be talked about is that if any arbitrarily small current can turn on the bulb, then the long wires used to completed the circuit are not actually necessary--you could just use an antenna--and in this light the explanation is already common knowledge. It would have helped to emphasize the role conductors in "shaping" the fields, and that they are absolutely necessary to deliver enough power to the bulb, which would not be receiving maximum power until the signal travelled all the way down the wire.

I love the comment section. People put arguments and ask great questions. Some even put interesting hypothetical cases related to this concept of energy flow. It makes the video even more interesting. It makes me realize that there are so many things about science that we haven’t even fully grasped on.