This video was sponsored by Caseta by Lutron. Imagine you have a giant circuit consisting of a battery, a switch, a light bulb, and two wires which are each 300,000 km long. That is the distance light travels in one second. So, they would reach out halfway to the moon and then come back to be connected to the light bulb, which is 1 meter away. Now, the question is, after I close this switch, how long would it take for the bulb to light up? Is it half a second, one second, two seconds, 1/c seconds, or none of the above? Now, you have to make some simplifying assumptions about this circuit, like the wires have to have no resistance, otherwise this wouldn't work, and the light bulb has to turn on immediately when current passes through it. But I want you to commit to an answer and put it down in the comments, so you can't say, oh yeah, I knew that was the answer when I tell you the answer later on. This question actually relates to how electrical energy gets from a power plant to your home. You know, unlike a battery, the electricity in the grid comes in the form of alternating current, or AC, which means electrons in the power lines are just wiggling back and forth. They never actually go anywhere. So, if the charges don't come from the power plant to your home, how does the electrical energy actually reach you? When I used to teach this subject, I would say that power lines are like this flexible plastic tubing, and the electrons inside are like this chain. So what a power station does is it pushes and pulls the electrons back and forth 60 times a second. Now, at your house, you can plug in a device like a toaster, which essentially means allowing the electrons to run through it. So when the power station pushes and pulls the electrons, well, they encounter resistance in the toaster element, and they dissipate their energy as heat, and so you can toast your bread. Now, this is a great story. I think it's easy to visualize, and I think my students understood it. The only problem is, it's wrong. For one thing, there is no continuous conducting wire that runs all the way from a power station to your house. No, there are physical gaps. There are breaks in the line, like in transformers, where one coil of wires wrapped on one side, a different coil of wire is wrapped on the other side. So, electrons cannot possibly flow from one to the other. Plus, I mean, if it's the electrons that are carrying the energy from the power station to your device, then when those same electrons flow back to the power station, why are they not also carrying energy back from your house to the power station? I mean, if the flow of current is two ways, then why does energy only flow in one direction? These are the lies you were taught about electricity, that electrons themselves have potential energy, that they are pushed or pulled through a continuous conducting loop, and that they dissipate their energy in the device. My claim in this video is that all of that is false. So, how does it actually work? In the 1860s and 70s, there was a huge breakthrough in our understanding of the universe when Scottish physicist James Clerk Maxwell realized that light is made up of oscillating electric and magnetic fields. The fields are oscillating perpendicular to each other and they are in phase, meaning when one is at its maximum, so is the other wave. Now, he works out the equations that govern the behavior of electric and magnetic fields, and hence these waves. Those are now called Maxwell's equations. But in 1883, one of Maxwell's former students, John Henry Poynting, is thinking about conservation of energy. Now, if energy is conserved locally in every tiny bit of space, well, then you should be able to trace the path that energy flows from one place to another. So, think about the energy that comes to us from the sun. I mean, during those eight minutes when the light is traveling, the energy is stored and being transmitted in the electric and magnetic fields of the light. Now, Poynting works out an equation to describe energy flux. That is, how much electromagnetic energy is passing through an area per second. This is known as the Poynting vector, and it's given the symbol S. And the formula is really pretty simple. It's just a constant, 1 over mu naught, which is the permeability of free space, times E cross B. Now, E cross B is the cross product of the electric and magnetic fields. Now, the cross product is just a particular way of multiplying two vectors together, where you multiply their perpendicular magnitudes, and to find the direction, you put your fingers in the direction of the first vector, which in this case is the electric field, and curl them in the direction of the second vector, the magnetic field, then your thumb points in the direction of the resulting vector, the energy flux. So what this shows us about light is that the energy is flowing perpendicular to both the electric and the magnetic fields, and it's in the same direction as the light is traveling. So, this makes a lot of sense. Light carries energy from its source out to its destination. But the kicker is this. Poynting's equation doesn't just work for light. It works anytime there are electric and magnetic fields coinciding. Anytime you have electric and magnetic fields together, there is a flow of energy, and you can calculate it using Poynting's vector. To illustrate this, let's consider a simple circuit with a battery and a light bulb. The battery by itself has an electric field, but since no charges are moving, there is no magnetic field, so the battery doesn't lose energy. When the battery is connected into the circuit, its electric field extends through the circuit at the speed of light. This electric field pushes electrons around, so they accumulate on some of the surfaces of the conductors, making them negatively charged, and are depleted elsewhere, leaving their surfaces positively charged. These surface charges create a small electric field inside the wires, causing electrons to drift preferentially in one direction. Note that this drift velocity is extremely slow, around a tenth of a millimeter per second. But this is current. Well, conventional current is defined to flow opposite the motion of electrons, but this is what's making it happen. The charge on the surfaces of the conductors also creates an electric field outside the wires. And the current inside the wires creates a magnetic field outside the wires. So, now there is a combination of electric and magnetic fields in the space around this circuit. So, according to Poynting's theory, energy should be flowing. And we can work out the direction of this energy flow using the right-hand rule. Around the battery, for example, the electric field is down and the magnetic field is into the screen. So you find the energy flux is to the right, away from the battery. In fact, all around the battery, you'll find the energy is radially outwards. Energy is going out through the sides of the battery into the fields. Along the wires, again, you can use the right-hand rule to find the energy is flowing to the right. This is true for the fields along the top wire and the bottom wire. But at the filament, the Poynting vector is directed in toward the light bulb. So the light bulb is getting energy from the field. If you do the cross product, you find the energy is coming in from all around the bulb. It takes many paths from the battery to the bulb, but in all cases, the energy is transmitted by the electric and magnetic fields. I mean, how far do the electrons go in this little thing you're talking about? They barely move. They probably don't move at all. So, there are a few things to notice here. Even though the electrons go two ways, away from the battery and towards it, by using the Poynting vector, you find that the energy flux only goes one way, from the battery to the bulb. This also shows it's the fields and not the electrons that carry the energy. I mean, how far do the electrons go in this little thing you're talking about? They barely move. They probably don't move at all. Now, what happens if in place of a battery, we use an alternating current source. Well, then the direction of current reverses every half cycle. But this means that both the electric and magnetic fields flip at the same time. So, at any instant, the Poynting vector still points in the same direction, from the source to the bulb. So, the exact same analysis we used for DC still works for AC. And this explains how energy is able to flow from power plants to homes in power lines. Inside the wires, electrons just oscillate back and forth. Their motion is greatly exaggerated here. But they do not carry the energy. Outside the wires, oscillating electric and magnetic fields travel from the power station to your home. You can use the Poynting vector to check that the energy flux is going in one direction. You might think this is just an academic discussion, that you could see the energy as transmitted either by fields or by the current in the wire. But that is not the case. And people learned this the hard way when they started laying undersea telegraph cables. The first transatlantic cable was laid in 1858. It only worked for about a month. It never worked properly. There are all kinds of distortions when they tried to send it. Enormous amounts of distortion. They could work it at a few words per minute. What they found was sending signals over such a long distance under the sea, the pulses became distorted and lengthened. It was hard to differentiate dots from dashes. To account for the failure, there was a debate among scientists. William Thomson, the future Lord Kelvin, thought electrical signals moved through submarine cables like water flowing through a rubber tube. But others, like Heaviside and Fitzgerald, argued it was the fields around the wires that carried the energy and information. And ultimately, this view proved correct. To insulate and protect the submarine cable, the central copper conductor had been coated in an insulator and then encased in an iron sheath. The iron was only meant to strengthen the cable, but as a good conductor, it interfered with the propagation of electromagnetic fields because it increased the capacitance of the line. This is why today most power lines are suspended high up. Even the damp earth acts as a conductor, so you want a large insulating gap of air to separate the wires from the ground. So, what is the answer to our giant circuit light bulb question? Well, after I close the switch, the light bulb will turn on almost instantaneously in roughly 1/c seconds. So, the correct answer is D. I think a lot of people imagine that the electric field needs to travel from the battery all the way down the wire, which is a light second long. So, it should take a second for the bulb to light up. Well, what we've learned in this video is it's not really what's happening in the wires that matters. It's what happens around the wires. And the electric and magnetic fields can propagate out through space to this light bulb, which is only 1 meter away in a few nanoseconds. And so, that is the limiting factor for the light bulb turning on. Now, the bulb won't receive the entire voltage of the battery immediately. It'll be some fraction, which depends on the impedance of these lines and the impedance of the bulb. Now, I asked several experts about this question and got kind of different answers, but we all agreed on these main points. So, I'm going to put their analysis in the description in case you want to learn more about this particular setup. If I get called out on it, people don't think it's real. We can, we can definitely invest the resources and and string up some lines and make our own power lines in the desert. You're going to get called out on it. I agree. I think you're going to get called out. I think that's right. I think it's just kind of wild that this is one of those things that we use every day that almost nobody thinks about or knows the right answer to. These traveling electromagnetic waves around power lines are really what's delivering your power. Hey, now that you understand how electrical energy actually flows, you can think about that every time you flick on a light switch. And if you want to take your switches to the next level, the sponsor of this video, Caseta by Lutron, provides premium smart lighting control, including switches, remotes, and plug-in smart dimmers. And since one switch can control many regular bulbs, you can effectively make all those bulbs smart just by replacing the switch. Then you can turn your lights on and off using your phone. Or you can use another device like Alexa or Google Assistant. Caseta works with more leading smart home brands than any other smart lighting control system. One of the things I like is setting timers. The lights in my office, for example, turn on by themselves every evening. And this feature gives you peace of mind that everyone in your household will always come home to a well-lit house. And once you're already in bed, you can check which lights you forgot to turn off and do that from your phone. Installation is easy. Make sure you turn off power to the switch first and then disconnect the existing wires and connect Caseta's smart switch. If you need any help, they're just a click or a call away. Learn more about Caseta at Lutron's website, lutron.com/veritasium. I will put that link down in the description. So, I want to thank Lutron Electronics for sponsoring this video, and I want to thank you for watching.
The video starts with an animation of Earth from space, then zooms in on a specific location, transitioning to a circuit diagram overlaying the Earth. The Caseta by Lutron logo appears.
"This video was sponsored by Caseta by Lutron."
A man in a green shirt and jeans crouches on a dirt path, gesturing with his hands towards a light bulb, a switch, and a battery connected by orange wires on the ground. The background shows a sprawling city and mountains under a clear sky.
"Imagine you have a giant circuit consisting of a battery, a switch, a light bulb, and two wires which are each 300,000 km long."
The man's hand is shown pressing a red clip onto the positive terminal of a black battery. The battery has a red plus sign and a white label. Orange wires are connected to the battery.
"That is the distance light travels in one second. So, they would reach out halfway to the moon and then come back to be connected to the light bulb, which is 1 meter away."
An overhead shot shows the man crouching, connecting wires to a light bulb and battery setup on the ground. Two long orange wires stretch out horizontally on either side. Text overlays appear, indicating '300,000 KM' with arrows pointing left and right, and a circuit diagram with Earth and the Moon.
"Now, the question is, after I close this switch, how long would it take for the bulb to light up?"
The man is shown crouching, looking directly at the camera, and gesturing with his right hand as if counting options. On-screen text presents multiple-choice answers A through E.
"Is it half a second, one second, two seconds, 1/c seconds, or none of the above?"
Close-up of the man's face as he explains the assumptions. The on-screen text with the multiple-choice answers remains visible.
"Now, you have to make some simplifying assumptions about this circuit, like the wires have to have no resistance, otherwise this wouldn't work, and the light bulb has to turn on immediately when current passes through it."
The scene transitions back to the circuit diagram overlaid on Earth in space, with the multiple-choice options still visible. The Earth rotates slowly, emphasizing the vast distances involved.
"But I want you to commit to an answer and put it down in the comments, so you can't say, oh yeah, I knew that was the answer when I tell you the answer later on."
The man stands in a brightly lit room, facing the camera, gesturing with his hands. He is wearing a green button-up shirt and a dark smartwatch. Two white light switches are visible on the wall to his right. The background is a white wall with a window showing greenery outside.
"This question actually relates to how electrical energy gets from a power plant to your home."
Close-up of the man's finger pressing the top part of a white light switch. The switch has a small LED indicator on the bottom.
"You know, unlike a battery, the electricity in the grid comes in the form of alternating current, or AC, which means electrons in the power lines are just wiggling back and forth."
The man holds a black battery with red and black terminals, looking at the camera. He is standing in the same room with white walls and a window in the background. He gestures with his free hand while speaking.
"They never actually go anywhere. So, if the charges don't come from the power plant to your home, how does the electrical energy actually reach you?"
An aerial shot of a large electrical substation with numerous power lines and transformers. The sun is low in the sky, casting long shadows and creating a warm glow. The substation is surrounded by green grass.
The man stands in a room with white pegboard walls, holding a small, clear plastic tube with a metal chain inside. He gestures with his hands to explain his analogy. A blue and grey wheel on a metal bracket is on the table to his right.
"When I used to teach this subject, I would say that power lines are like this flexible plastic tubing. And the electrons inside are like this chain."
The man demonstrates with the plastic tube and chain, pulling and pushing the chain back and forth through the tube. A blue and grey wheel on a metal bracket is positioned over the tube, acting as a resistance point. The chain moves, showing the concept of alternating current.
"So what a power station does is it pushes and pulls the electrons back and forth 60 times a second."
The man holds the blue and grey wheel, explaining its function. He then places it back onto the plastic tube, over the chain. He gestures with his hands, indicating the movement of the chain through the wheel.
"Now, at your house, you can plug in a device like a toaster, which essentially means allowing the electrons to run through it."
The man pulls and pushes the chain through the plastic tube again, with the wheel acting as resistance. The chain moves back and forth, illustrating the dissipation of energy as heat. He gestures with his hands to emphasize the concept.
"So when the power station pushes and pulls the electrons, well, they encounter resistance in the toaster element, and they dissipate their energy as heat, and so you can toast your bread."
The man gestures broadly with his hands, indicating the entire setup on the table. He then points to himself, emphasizing his past teaching method, before revealing the flaw in the analogy. He looks directly at the camera with a serious expression.
"Now, this is a great story. I think it's easy to visualize, and I think my students understood it. The only problem is, it's wrong."
The man gestures with his hands to illustrate the concept of gaps in the electrical line. He uses his fingers to represent the coils of a transformer, showing that electrons cannot flow directly between them. He maintains a serious and explanatory expression.
"For one thing, there is no continuous conducting wire that runs all the way from a power station to your house. No, there are physical gaps. There are breaks in the line, like in transformers, where one coil of wires wrapped on one side, a different coil of wire is wrapped on the other side. So, electrons cannot possibly flow from one to the other."
The man again demonstrates with the plastic tube and chain, pulling and pushing the chain. He emphasizes the two-way movement of the chain and questions why energy would only flow in one direction if electrons were the sole carriers. He looks directly at the camera with a questioning expression.
"Plus, I mean, if it's the electrons that are carrying the energy from the power station to your device, then when those same electrons flow back to the power station, why are they not also carrying energy back from your house to the power station?"
Close-up of the man's hands pulling and pushing the chain through the plastic tube, with the wheel acting as resistance. The chain moves back and forth, illustrating the two-way flow of electrons.
"I mean, if the flow of current is two ways, then why does energy only flow in one direction?"
The man stands in the room, gesturing with his hands. He looks directly at the camera with a serious expression, emphasizing that previous teachings about electricity are incorrect. He uses his hands to illustrate the concepts he is refuting.
"These are the lies you were taught about electricity, that electrons themselves have potential energy, that they are pushed or pulled through a continuous conducting loop, and that they dissipate their energy in the device."
The man stands in the room, gesturing broadly with his hands, emphasizing that his previous explanation of electricity is incorrect. He looks directly at the camera with a serious expression.
"My claim in this video is that all of that is false."
The man stands in the room, gesturing with his hands, posing a question to the audience. He looks directly at the camera with an inquisitive expression.
"So, how does it actually work?"
The man walks towards the camera on a dirt path, with a city skyline visible in the distance at dusk. He gestures with his hands as he speaks, explaining the historical context of electromagnetic theory. The sky is a gradient of purple and orange.
"In the 1860s and 70s, there was a huge breakthrough in our understanding of the universe when Scottish physicist James Clerk Maxwell realized that light is made up of oscillating electric and magnetic fields. The fields are oscillating perpendicular to each other and they are in phase, meaning when one is at its maximum, so is the other wave."
A black and white portrait of James Clerk Maxwell, a man with a full beard and a dark suit, appears on screen. The text 'JAMES CLERK MAXWELL' is displayed below his portrait.
"Now, he works out the equations that govern the behavior of electric and magnetic fields, and hence these waves. Those are now called Maxwell's equations."
The man stands on a dirt path with a city skyline in the distance at dusk, holding a green laser pointer. He points the laser, and a visual representation of oscillating electric (red) and magnetic (blue) fields appears, moving along a green line. Text labels 'E FIELD' and 'B FIELD' are visible.
"But in 1883, one of Maxwell's former students, John Henry Poynting, is thinking about conservation of energy."
The animated electromagnetic wave continues to propagate. Maxwell's equations are displayed on the left side of the screen, detailing the mathematical relationships governing electric and magnetic fields.
"Now, if energy is conserved locally in every tiny bit of space, well, then you should be able to trace the path that energy flows from one place to another."
The man stands on a dirt path with a city skyline in the distance at dusk, gesturing with his hands. He is holding a small black object, possibly a remote or a microphone. He looks directly at the camera with a thoughtful expression.
"So, think about the energy that comes to us from the sun. I mean, during those eight minutes when the light is traveling, the energy is stored and being transmitted in the electric and magnetic fields of the light."
A black and white portrait of John Henry Poynting, a man with a mustache and a suit, appears on screen. The text 'JOHN HENRY POYNTING' is displayed below his portrait.
"Now, Poynting works out an equation to describe energy flux. That is, how much electromagnetic energy is passing through an area per second."
A close-up of the sun, a bright orange sphere against a black background, is shown. A green laser beam emerges from the sun, and oscillating electric (red) and magnetic (blue) fields propagate along the beam. The formula S = 1/μ₀ E × B appears on screen, with 'ENERGY / AREA·TIME' and 'POYNTING VECTOR' labels.
"This is known as the Poynting vector, and it's given the symbol S. And the formula is really pretty simple. It's just a constant, 1 over mu naught, which is the permeability of free space, times E cross B."
The man stands on a dirt path with a city skyline in the distance at dusk. The formula S = 1/μ₀ E × B is displayed on screen. He gestures with his hands, explaining the cross product of electric and magnetic fields, illustrating the right-hand rule. The animated electromagnetic wave is superimposed over his hands.
"Now, E cross B is the cross product of the electric and magnetic fields."
The man stands on a dirt path with a city skyline in the distance at dusk. The formula S = 1/μ₀ E × B is displayed on screen. He demonstrates the right-hand rule with his hand, showing how the direction of energy flux is determined from the electric and magnetic fields. The animated electromagnetic wave is superimposed over his hands, with a yellow arrow indicating the energy flux direction.
"Now, the cross product is just a particular way of multiplying two vectors together, where you multiply their perpendicular magnitudes, and to find the direction, you put your fingers in the direction of the first vector, which in this case is the electric field, and curl them in the direction of the second vector, the magnetic field, then your thumb points in the direction of the resulting vector, the energy flux."
The man stands on a dirt path with a city skyline in the distance at dusk, holding a small black object. He gestures with his hands, explaining the direction of energy flow in light. He looks directly at the camera with a confident expression.
"So what this shows us about light is that the energy is flowing perpendicular to both the electric and the magnetic fields, and it's in the same direction as the light is traveling. So, this makes a lot of sense."
The man holds a small black object, possibly a remote or microphone, in his right hand. He gestures with his left hand towards the distant city lights, illustrating the concept of energy traveling from source to destination. He looks directly at the camera with a confident expression.
"Light carries energy from its source out to its destination."
The man holds up the small black object, emphasizing his point. He looks directly at the camera with a serious expression, highlighting the broader applicability of Poynting's equation.
"But the kicker is this. Poynting's equation doesn't just work for light. It works anytime there are electric and magnetic fields coinciding."
The man gestures with his hands, emphasizing the constant presence of energy flow when electric and magnetic fields coincide. He looks directly at the camera with a confident and explanatory expression.
"Anytime you have electric and magnetic fields together, there is a flow of energy, and you can calculate it using Poynting's vector."
The scene transitions to a black background with a simple circuit diagram: a battery on the left, a light bulb on the right, connected by a rectangular wire loop. The light bulb is off.
"To illustrate this, let's consider a simple circuit with a battery and a light bulb."
The circuit diagram disappears, leaving only the battery. Red lines with arrows, representing the electric field, emerge from the positive terminal and curve around to enter the negative terminal, forming a symmetrical pattern.
"The battery by itself has an electric field, but since no charges are moving, there is no magnetic field, so the battery doesn't lose energy."
The circuit diagram reappears with the battery and light bulb. Red plus signs appear along the top wire, and green minus signs appear along the bottom wire, indicating the electric field extending through the circuit.
"When the battery is connected into the circuit, its electric field extends through the circuit at the speed of light."
A close-up of the bottom left corner of the circuit shows green dots (electrons) moving along the wire, accumulating at certain points. Red plus signs and green minus signs are visible on the wire surfaces, indicating charge distribution. The light bulb is still off.
"This electric field pushes electrons around, so they accumulate on some of the surfaces of the conductors, making them negatively charged, and are depleted elsewhere, leaving their surfaces positively charged."
A close-up of a segment of the wire shows green dots (electrons) drifting to the right inside the wire. Red plus signs are visible on the outside surfaces of the wire. A red arrow labeled 'E' indicates the direction of the electric field inside the wire.
"These surface charges create a small electric field inside the wires, causing electrons to drift preferentially in one direction."
The close-up of the wire segment continues, with green dots (electrons) drifting to the right. A green arrow labeled 'I' appears above the wire, pointing left, indicating the conventional current direction. The red arrow 'E' for the electric field remains.
"Note that this drift velocity is extremely slow, around a tenth of a millimeter per second. But this is current. Well, conventional current is defined to flow opposite the motion of electrons, but this is what's making it happen."
The full circuit diagram is shown. Red lines with arrows, representing the electric field, curve around the outside of the wires. Blue circles with arrows, representing the magnetic field, appear around the wires, perpendicular to the current flow. The light bulb is still off.
"The charge on the surfaces of the conductors also creates an electric field outside the wires. And the current inside the wires creates a magnetic field outside the wires."
The full circuit diagram is shown with both electric (red lines) and magnetic (blue circles) fields. Yellow arrows, representing the Poynting vector, appear, showing energy flowing from the battery, through the space around the wires, and towards the light bulb. The light bulb is still off.
"So, now there is a combination of electric and magnetic fields in the space around this circuit. So, according to Poynting's theory, energy should be flowing."
A close-up of the battery in the circuit is shown with electric (red) and magnetic (blue) fields. A human hand appears, demonstrating the right-hand rule to show how the energy flux (yellow arrow labeled 'S') is directed to the right, away from the battery.
"And we can work out the direction of this energy flow using the right-hand rule. Around the battery, for example, the electric field is down and the magnetic field is into the screen. So you find the energy flux is to the right, away from the battery."
The close-up of the battery continues, with yellow arrows (Poynting vector) now showing energy radiating outwards from all sides of the battery, into the surrounding electric (red) and magnetic (blue) fields.
"In fact, all around the battery, you'll find the energy is radially outwards. Energy is going out through the sides of the battery into the fields."
The scene shifts to a close-up of a segment of the top wire, with electric (red) and magnetic (blue) fields. A human hand appears, demonstrating the right-hand rule to show the energy flux (yellow arrow labeled 'S') flowing to the right along the wire.
"Along the wires, again, you can use the right-hand rule to find the energy is flowing to the right. This is true for the fields along the top wire and the bottom wire."
The full circuit diagram is shown with all electric (red), magnetic (blue), and energy flux (yellow) fields. The yellow arrows now converge into the light bulb's filament, indicating energy flowing into the bulb from all directions. The light bulb glows brightly.
"But at the filament, the Poynting vector is directed in toward the light bulb. So the light bulb is getting energy from the field."
The full circuit diagram with all fields is shown, with yellow arrows (energy flux) flowing from the battery and converging into the light bulb. The light bulb is glowing. The arrows illustrate the complex paths of energy flow through the surrounding space.
"If you do the cross product, you find the energy is coming in from all around the bulb. It takes many paths from the battery to the bulb, but in all cases, the energy is transmitted by the electric and magnetic fields."
Dr. Bruce Hunt, an Associate Professor in the History of Science at UT Austin, is shown in a video call. He has a grey beard and glasses, wearing a light grey polo shirt. He smiles and gestures with his hands as he speaks, emphasizing his point.
"People seem to think that you're pumping electrons and that you're like buying electrons or something, which is just so wrong."
The man from the video is shown on a video call, listening intently to Dr. Bruce Hunt. He is wearing a blue t-shirt and sitting in a desk chair. A ring light and microphone are visible in the background.
"For most people, I think to this day, it's quite counterintuitive to think that the energy is flowing through the space around the conductor."
Dr. Bruce Hunt is shown in a video call, speaking directly to the camera. He maintains a serious expression, emphasizing his point about energy flow. The date '2021-11-09 11:14:55' is visible in the bottom right corner.
"But the the energy is, which is traveling through the field, yeah, it's going quite fast."
The full circuit diagram with all fields is shown, with yellow arrows (energy flux) flowing from the battery and converging into the light bulb. The light bulb is glowing. The arrows illustrate the complex paths of energy flow through the surrounding space.
"So there are a few things to notice here. Even though the electrons go two ways, away from the battery and towards it, by using the Poynting vector, you find that the energy flux only goes one way, from the battery to the bulb."
Dr. Bruce Hunt is shown in a video call, smiling and gesturing with his hands as he speaks, emphasizing that electrons barely move in a circuit. The date '2021-11-09 11:07:07' is visible in the bottom right corner.
"I mean, how far do the electrons go in this little thing you're talking about? They barely move. They probably don't move at all."
The circuit diagram is shown on a black background, with a battery and a light bulb. The light bulb is off. The battery is then replaced by an 'AC' source, represented by a grey box with knobs.
"Now, what happens if in place of a battery, we use an alternating current source?"
The circuit diagram with the AC source is shown. Electric (red) and magnetic (blue) fields appear around the wires. The charges (red plus and green minus signs) and the field directions (arrows) flip back and forth, indicating alternating current. The light bulb is still off.
"Well, then the direction of current reverses every half cycle. But this means that both the electric and magnetic fields flip at the same time."
The circuit diagram with the AC source is shown, with electric (red), magnetic (blue), and energy flux (yellow) fields. The yellow arrows consistently point from the AC source to the light bulb, even as the electric and magnetic fields flip. The light bulb glows.
"So, at any instant, the Poynting vector still points in the same direction, from the source to the bulb. So, the exact same analysis we used for DC still works for AC."
A close-up of two parallel golden wires is shown against a dark blue background. Green dots (electrons) oscillate back and forth along the wires. Red arrows, representing the electric field, also oscillate between the wires, perpendicular to the electron motion.
"And this explains how energy is able to flow from power plants to homes in power lines. Inside the wires, electrons just oscillate back and forth. Their motion is greatly exaggerated here."
The close-up of the two parallel golden wires continues. Now, blue arrows, representing the magnetic field, also oscillate between the wires, perpendicular to both the electric field and the direction of energy flow. The green dots (electrons) continue to oscillate along the wires.
"But they do not carry the energy. Outside the wires, oscillating electric and magnetic fields travel from the power station to your home."
The close-up of the two parallel golden wires continues with oscillating electric and magnetic fields. The energy flux (yellow arrows) is consistently shown traveling in one direction, from left to right, between the wires.
"You can use the Poynting vector to check that the energy flux is going in one direction. You might think this is just an academic discussion, that you could see the energy as transmitted either by fields or by the current in the wire. But that is not the case."
A black and white archival footage shows men on a ship, working with thick cables. The ship is moving through choppy water. The men are dressed in work clothes and hats, pulling and guiding the heavy cables.
"And people learned this the hard way when they started laying undersea telegraph cables. The first transatlantic cable was laid in 1858."
A map of the submarine telegraph between America and Europe is shown. The map details the transatlantic cable routes and dates of laying. The map is old and has a faded, antique appearance.
"It only worked for about a month. It never worked properly. There are all kinds of distortions when they tried to send it."
Dr. Bruce Hunt is shown in a video call, speaking directly to the camera. He looks serious and emphasizes the 'enormous amounts of distortion' in the early telegraph cables. The date '2021-11-09 11:34:16' is visible.
"Enormous amounts of distortion. They could work it at a few words per minute."
Black and white archival footage shows a small tugboat pulling a large, heavy cable from the shore into the sea. Men are visible on the boat, working with the cable. The sea is calm, and the sky is overcast.
"What they found was sending signals over such a long distance under the sea, the pulses became distorted and lengthened. It was hard to differentiate dots from dashes."
A black and white portrait of William Thomson, Lord Kelvin, a man with a long white beard and a dark suit, appears on screen. The text 'WILLIAM THOMSON' is displayed below his portrait.
"To account for the failure, there was a debate among scientists. William Thomson, the future Lord Kelvin, thought electrical signals moved through submarine cables like water flowing through a rubber tube."
A split screen shows black and white portraits of Oliver Heaviside (left) and GF Fitzgerald (right). Heaviside has a serious expression and a mustache. Fitzgerald has a long beard and a thoughtful expression. Their names are displayed below their portraits.
"But others, like Heaviside and Fitzgerald, argued it was the fields around the wires that carried the energy and information. And ultimately, this view proved correct."
Black and white archival footage shows several men on a ship, working with large coils of cable. They are pulling and arranging the cables on the deck. The ship's structure and windows are visible in the background.
"To insulate and protect the submarine cable, the central copper conductor had been coated in an insulator and then encased in an iron sheath."
A close-up of a segment of the submarine cable is shown. It consists of multiple twisted wires, encased in a brass band with engraved text. The cable appears strong and durable.
"The iron was only meant to strengthen the cable, but as a good conductor, it interfered with the propagation of electromagnetic fields because it increased the capacitance of the line."
Black and white archival footage shows several men pulling a thick cable along a sandy shore, towards a body of water. Industrial buildings and smokestacks are visible in the background. The men are working hard to move the heavy cable.
"This is why today most power lines are suspended high up. Even the damp earth acts as a conductor, so you want a large insulating gap of air to separate the wires from the ground."
An aerial shot shows a vast landscape with a road, dense forests, and a large body of water under an overcast sky. Numerous power lines on tall pylons stretch across the landscape, emphasizing the long distances involved in power transmission.
"So, what is the answer to our giant circuit light bulb question?"
The man crouches on the dirt path, gesturing towards the light bulb and battery setup. The light bulb is now glowing brightly. On-screen text displays the multiple-choice options, with 'D) 1/c s' highlighted as the correct answer.
"Well, after I close the switch, the light bulb will turn on almost instantaneously in roughly 1/c seconds. So, the correct answer is D."
The man crouches on the dirt path, gesturing towards the light bulb and battery setup. The light bulb is glowing. He looks directly at the camera, explaining the common misconception.
"I think a lot of people imagine that the electric field needs to travel from the battery all the way down the wire, which is a light second long. So, it should take a second for the bulb to light up."
The circuit diagram with Earth and the Moon is shown again, with the light bulb on. The man's voiceover explains that the energy transmission is not about the wires themselves, but the fields around them.
"Well, what we've learned in this video is it's not really what's happening in the wires that matters. It's what happens around the wires."
The man crouches on the dirt path, gesturing broadly with his hands to emphasize the propagation of electromagnetic fields through space. The light bulb is glowing. He looks directly at the camera with a confident expression.
"And the electric and magnetic fields can propagate out through space to this light bulb, which is only 1 meter away in a few nanoseconds. And so, that is the limiting factor for the light bulb turning on."
A close-up of the glowing light bulb on the black box is shown. The light bulb emits a soft white glow. The background is a blurry landscape at dusk.
"Now, the bulb won't receive the entire voltage of the battery immediately. It'll be some fraction, which depends on the impedance of these lines and the impedance of the bulb."
The man crouches on the dirt path, gesturing towards the light bulb and battery setup. The light bulb is glowing. He looks directly at the camera, explaining that the voltage received by the bulb is a fraction of the battery's voltage, depending on impedance.
"Now, I asked several experts about this question and got kind of different answers, but we all agreed on these main points. So, I'm going to put their analysis in the description in case you want to learn more about this particular setup."
A graph with two lines (blue and red) showing voltage over time is displayed. Dr. Richard Abbott from LIGO Caltech is shown in a video call, gesturing with his hand and touching his neck as he speaks, discussing the expert analysis.
"If I get called out on it, people don't think it's real. We can, we can definitely invest the resources and and string up some lines and make our own power lines in the desert."
The man from the video is shown in a video call, listening to the expert's feedback. He is wearing a black t-shirt. A neon 'Ve' sign is visible on the wall behind him. The date '2021-11-12 10:54' is visible.
"You're going to get called out on it. I agree. I think you're going to get called out."
Dr. Karl Berggren, Professor of Electrical Engineering at MIT, is shown in a video call. He has a beard and is wearing a grey t-shirt. A guitar is visible in the background. The date '2021-11-12 10:54' is visible.
"I agree, I think you're going to get called out."
Dr. Robert Olsen, Professor Emeritus of Electrical Engineering at WSU, is shown in a video call. He has white hair and glasses, wearing a dark shirt. He touches his chin thoughtfully as he speaks. The date '2021-11-12 10:54' is visible.
"I think that's right."
The man from the video is shown in a video call, covering his face with his hands, then looking up and smiling. He appears amused by the experts' reactions. The date '2021-11-12 10:55' is visible.
"I think it's just kind of wild that this is one of those things that we use every day that almost nobody thinks about or knows the right answer to."
The man crouches on the dirt path, gesturing towards the light bulb and battery setup. The light bulb is glowing. He looks directly at the camera, emphasizing that electromagnetic waves deliver power.
"These traveling electromagnetic waves around power lines are really what's delivering your power."
The video transitions to a blue background with a grid-like pattern. The 'Ve' logo for Veritasium appears, along with a list of names. The background then changes to a dark room with a glowing blue grid and stars.
"Hey, now that you understand how electrical energy actually flows, you can think about that every time you flick on a light switch."
The man sits at a desk in a well-lit room, gesturing with his hands. He is wearing a green button-up shirt. Behind him are framed insect specimens and a globe. A Caseta by Lutron smart home kit is on the desk. The 'Ve' logo is in the top left corner, and the 'Caseta by Lutron' logo is in the top right.
"And if you want to take your switches to the next level, the sponsor of this video, Caseta by Lutron, provides premium smart lighting control, including switches, remotes, and plug-in smart dimmers."
Close-up of a hand pressing a white light switch on a wall. The switch has multiple buttons and an LED indicator.
"And since one switch can control many regular bulbs, you can effectively make all those bulbs smart just by replacing the switch."
The man is shown installing a smart switch in a small, dark room with a circular light fixture. He then crouches to install another smart switch into a wall outlet. He demonstrates how to use a remote control to operate the lights.
"Then you can turn your lights on and off using your phone. Or you can use another device like Alexa or Google Assistant."
The man sits at a desk, gesturing with his hands. He is holding a small remote control. The Caseta by Lutron smart home kit is on the desk. The 'Ve' logo is in the top left corner, and the 'Caseta by Lutron' logo is in the top right.
"Caseta works with more leading smart home brands than any other smart lighting control system. One of the things I like is setting timers. The lights in my office, for example, turn on by themselves every evening."
A hand scrolls through a menu on a smartphone, showing options for setting timers for lights. The screen displays 'Schedule' and options for days of the week and times. The background is a blurry, dark room.
"And this feature gives you peace of mind that everyone in your household will always come home to a well-lit house. And once you're already in bed, you can check which lights you forgot to turn off and do that from your phone."
The man sits at a desk, gesturing with his hands. He is holding a small remote control. The Caseta by Lutron smart home kit is on the desk. The 'Ve' logo is in the top left corner, and the 'Caseta by Lutron' logo is in the top right.
"Installation is easy. Make sure you turn off power to the switch first and then disconnect the existing wires and connect Caseta's smart switch."
A hand scrolls through a smartphone screen, showing a list of lights and an option to 'Turn All Lights Off'. The hand then taps the button to turn off all lights. The background is a blurry, dark room.
"If you need any help, they're just a click or a call away. Learn more about Caseta at Lutron's website, lutron.com/veritasium. I will put that link down in the description. So, I want to thank Lutron Electronics for sponsoring this video, and I want to thank you for watching."