How Wrong Is VERITASIUM? A Lamp and Power Line Story

Hi, Derek from Veritasium made a video where he goes into my electronics territory and asks a question at the beginning and gives an answer at the end and his answer is

wrong

. You should watch Derek's video to see the full context. Of course, his video is excellent and very educational. but his question enveloped me in a way that I didn't like. It wasn't just a physics question, it was a complicated question. Look, if you want to increase your IQ, you get a book and a lot from my link in the description, thanks to My Godfather you hear more at the end, but a trick question is designed to deceive, not to test your knowledge.

Sort of like a baby is hungry and will die now if she is not fed and the mother is nowhere to be seen. What do we do? Don't know. We put on a breast and feed the baby without a pacifier, we open the closet door, the mom is there, hell, Derek's question was imagine you have a giant circuit that consists of a battery, a switch, a light bulb and two

power

wires. 300,000 kilometers long each. that is the distance that light travels in one second, well, more so now the question is, when we activate the switch, does it take half a second, one second, two seconds, one over c seconds or none of the above for the

lamp

turns on? c is the speed of light and one over c comes from the distance of one meter between the cables over c meters per second, so the value of 1 over c would be the value of time per second.

We also make some assumptions, such as that the wires should have no resistance. and the bulb has to turn on immediately when current passes through it, so I jump straight to the wires with no resistance. It is possible to make it with superconducting material, put it in the shade of a giant umbrella or the earth, keep it super cold and super. The light conduction should be turned on immediately as soon as there is

power

. Its

lamp

is normal, it can be incandescent or LED and it consumes a certain level of current when turned on. It takes some time for there to be operating current in the lamp. when it is on, but let's assume it is a special lamp and it will be fully on as soon as there is operating current and of course it will not turn on if there is not enough current through it for the operating currents that the electric waves would have to travel. the entire length of the loop at the speed of light, so it could take at least a second or more depending on After I close the switch, the light bulb will turn on in about one in c seconds, and my IQ was shattered .

That's when I understood when he said and the bulb has to turn on immediately when the current passes through it, it means the light turns on at any current level immediately, little derrick, that was a trick question, right? So that's what the mysterious black box is. for something that turns on the lamp immediately at any current level, actually with that assumption Derek's answer is

wrong

, the correct answer is none of the above the light never goes off regardless of the state of the switch when the switch is turned off with The voltage across it will eventually be the same as the battery voltage, which means there are electric fields across the switch contacts that attract the electrons.

Some electrons will jump the gap and result in an extremely small continuous leakage current. Derrick never said there is no leakage current and it's a real thing, the light turns on with any current so it's always on and I win, I'm not going to lie. Derek's response triggered me a bit so I was thinking about it for over a week, every day and night, which is good because it brought back a lot of lost memories, thanks Derek, let's dive into Derek's video because I don't entirely agree with every point you raise here. He says that in school they taught us something bad: that in an AC circuit the flow of electrons is like a chain that moves back and forth delivering energy to the load, if it is the electrons that transport the energy from the power plant to your device, so when those same electrons flow back to the power plant, why don't they also carry energy back from your home to the power plant?

I'm cutting wood pushing and pulling both acts where I put energy into the saw cutting the wood the saw is a vessel for transferring energy like electrons in a wire just because I pull doesn't mean I'm gaining energy these are the lies we were taught about electricity, come on, lies, that the electrons themselves have potential energy. I think this is debatable and depends on your frame of reference. I hope the rest of my video makes it clearer that they are pushed or pulled through a continuous conductive circuit in a closed loop with no capacitive or inductive brakes, they operate in a closed loop and dissipate their energy in the device, they help dissipate sources of energy in the load.

Those analogies may make sense, so I don't think calling them lies is accurate. this video is that all of that is false, I think Derek is exaggerating a lot, which is appealing to the general audience, but I think professionals expect a little more precision than he talks about the true flow of energy from source to load, that segment is highly inspired by a science asylum video I had seen a couple of years ago and which Derek also attributed to another excellent YouTube channel that you should subscribe to. In that segment, he talks about the pointing vector, not the pointer, the scientists who came up with it in an electrical system.

In the circuit, the pointing vector shown as s indicates the power flow with a unit of watt per square meter and is equal to a constant multiplied by the cross multiplication of the electric and magnetic field vectors, so it is used the right hand rule if the direction of the fingers coincides with the e. The vector y curves towards the vector b. The thumb shows the direction of power or energy flow per second. Directly, it shows that in a closed circuit of a circuit where we have electric fields between the wires and magnetic fields around the wires depending on the pointing vector.

In fact, electrical energy flows in the space around the cables by electromagnetic fields from the source to the load, which is true, but what is shown here is again exaggerated: it shows all energy vectors with the same strength . We know that in a straight cable the magnetic field The intensity of the field is inversely proportional to its distance from the cable, so a field 10 centimeters away is 100 times weaker than a field one millimeter away from the cable. Yes, maybe the electric fields are uniform between the wires, but the magnetic fields are much stronger closer together. to wires, especially for DC, the power flow looks more like this, with power much more concentrated near the wires and at much smaller levels further away from the wires.

AC is a different beast, although as the frequency increases, energy will find and radiate through many different capacitive and inductive parasitic pathways to the load or to the environment. Let me show you how crazy the world of AC is. I have a loop of cable connected nowhere, just an LED at the end and a five megahertz signal going out of range and if I connect the signal only to the LED, either on this side or the other side, it turns on without connection to earth, this also shows that it is the fields and not the electrons that carry the energy back.

The frame of reference is important, a counterargument. It's already in Derek's video, the current inside the wires creates a magnetic field outside the wires, so if the flow of electrons creates magnetic fields, why do we say that inside the wires the electrons just oscillate forward and backwards but they do not transport energy? Yes, the fields carry energy, but the current inside the wires creates a magnetic field outside the wires, so we conclude that, but what we have learned in this video, it is not really what happens in the wires that matter, it is directly contradicted by the current inside the wires which creates a magnetic field.

Outside the wires, electric fields are an inherent property of electrons or protons, in fact creating electric fields around the wires, the movement of these charges creates magnetic fields around the wires and then the fields carry the energy , so to speak, it is the fields and not the electrons that carry the energy sounds inaccurate, enough with the secondary mission, let's focus on the main issue of long cables. I'm going to provide detailed information that is sure to blow your mind, so save your minds now if you must and just watch my sponsor. segment at the end, but if I see a drop in my audience, you are just a bunch of traitors.

I reviewed the analysis that dr. olsen and dr. abbott provided to derek in the video of him. I also did a lot of simulations and analysis and was happy. To see that my results match theirs, I also checked a few things with Dave from the eev blog to make sure I'm not completely crazy. Thanks Dave for the videos on the subject. Subscribe to his channel too, but I'm not going to do that. Now I say the same things as other people. Let's get super basic and replace these super long cables with their equivalent impedances. We don't know what they are and we don't care as long as there is no other way important to the different parties. of the circuit to exchange energy if current enters here the same current must leave here almost immediately limited by the speed of light so Derek is right that as soon as we close the switch we have current through the lamp in one meter for c seconds.

Because the wires are only one meter apart, it doesn't matter how long they are in the loop, but rather how much current depends on these components. Now let's dig deeper, the circuit is symmetrical on both sides and what happens on one side happens on the other side. in the opposite direction, so let's focus on one side, the switch has been off long enough for the negativity to have spread through all the wires, just a little bit of positive charges here and when we close the switch, suddenly, a burst of positivity travels in the wire at the speed of light after the burst of current travels one meter at the speed of light, the new electric fields finally reach the opposite wire and start pulling the electrons up here, making them which means that at that moment we have current flowing into the lamp, what are the charges that attract the charges to each other? two surfaces is a capacitor current that runs through the wire creating magnetic fields and self-inductance of the soul is an inductor this is how we engineers manage the fields around circuits and group them into more digestible components so that many can model this long wire stages of inductors and capacitors, each for a defined length of wire, and as the wave travels into this network it encounters more and more of these stages, the inductance that blocks the current and the capacitance that absorbs the charges is the reason by which the burst of current flattens out as it travels through the

line

for the moment we look at the energy vectors pointing shortly after we flip the switch and the field waves appear in the wire at the speed of light not yet You know what we have at the end of the cable, all you see is a uniform network of impedances, if we draw the energy vectors around the cables of the loop, we see that they all point towards the loop and nothing comes out, as if it were a giant resistance that absorbs all the energy only after half a second of travel.

Along the wire these waves hit the short circuit at the end, some of them are reflected and travel for another half second to add up the energy entering the lamp so that the waves can travel and reflect several times and these

line

s are half light second in duration, it can take anywhere from one to several seconds before the light receives full power from the source, at which point the entire length of the wire is at the same potential level, so there are no electric fields connecting them , just electric fields connecting the positive side to the negative side.

A line like this is called a transmission line and if we ignore the resistances of the wires and the leakage between the wires and the line goes to infinity, then the impedance of this circuit is in fact a resistance equal to the square root of two of these some divided. by a c, but if this really goes to infinity, then the impedance seen from this point on is no different from the impedance at the beginning, so we can remove the rest of the line and replace it with a single resistor equal to the impedance of line that a transmitter would have.

Let's look at the same line as if the energy was just coming in without reflections, meaning that one receiver would be absorbing all the energy. Now, if the transmitter also has the same impedance matched to the line, we would have maximum power transfer between the transmitter and the receiver, but that's another

story

, so let's go back to our linesjust when we close the switch and the waves have not been reflected from behind, but this line looks like a resistance at the input, so as soon as the switch is closed and the waves propagate at the speed of Turn on the voltage of the lamp jumps to its known level abruptly without any additional overshoots or delays, although this is not the full battery voltage due to these resistances and the only way to get rid of these resistances is to make the length of the connecting wires zero, so So if you have any length of wire initially, it looks like a resistance until the waves reflect from the end and send back the information that we were fooled.

It's a short circuit. Let me show you a simulation. The simulation does not actually represent the dimensions or effects of the circuit. of the speed of light but correctly demonstrates the LC propagation delays in the circuit. Don't look if you have diarrhea. I tried to model 40 kilometers of round trip cable or 20 kilometers of transmission line. I roughly calculated inductors and capacitors based on one kilometer segments of the line, assuming my wires are one centimeter thick, one meter away the supply is 10 volts and the lamp is 100 ohms, so , like a one watt lamp it is reasonable to run the simulation, this is the voltage across the lamp that you see when I turn on the battery, the voltage rises slowly and takes maybe more than 15 milliseconds to settle close to the battery voltage and this is just a 20 kilometer transmission line and that's not the whole

story

if I zoom in I see that the voltage is actually increasing in steps this is the first very flat step around 65 millivolts indicating that the line is acting as a resistor here the supply turns on and the waves travel all the way and hit the short circuit here and come back carrying the information and we enter the next step, so any length of transmission line is a momentary resistance at high speeds, that's not is the whole story if I get right to the beginning you will see that initially I have a voltage spike close to the battery voltage because my supply increases in a nanosecond and then slowly increases towards the first step.

Both the spike and the ramp to the step are inaccuracies because In my model I put in first the line capacitance which acts as a short circuit at high speed that creates the voltage spike and then discharges, then the inductance causes the ramp to the first passed. However, this does not affect the overall result, but the truth is that the inductors and capacitors exist on the line at the same time, the simulation would be much more accurate but almost impossible if we made our segments much smaller, perhaps every one micrometer in instead of a kilometer, until the circuit approaches a true resistance property.

All these oscillations are also Anyway, due to an inexact model, if I change the inductance and capacitance value so that the line impedance matches half the impedance of the lamp or both lines together match the resistance of the lamp lamp and pretend that you would see that the lamp voltage would immediately jump to half of the supply voltage that there would be. without ringing and after the wave completed a round trip across the line, the voltage would jump to full supply voltage. This is the best case for Derek's question, the lamp voltage would immediately jump to a decent voltage at the speed of light and after a second 300 kilometer round trip, it would jump to the maximum voltage, but with values ​​chosen more reasonably for our case, where nothing matches correctly, it will take several steps for the lab voltage to stabilize and each of these steps lasts a second, so where would it be? you choose your threshold voltage and current to turn the lamp on low after one second on high after 10 seconds or to reach your threshold over c seconds it just says any current turns on the lamp and forgets to address the existence of leakage current that would keep the lamp on forever, so Derek's answer was incorrect, yes, on a minor technicality and because he tried to trick me into giving the wrong answer, but his question raises great insight into electromagnetic waves.

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