The Big Misconception About Electricity

This video was sponsored by Caséta de Lutron. Imagine you have a giant circuit consisting of a battery, a switch, a light bulb, and two wires each 300,000 kilometers long. That is the distance light travels in one second. So they would go halfway to the moon and then come back to connect to the light bulb, which is a meter away. Now the question is, after closing this switch, how long will it take for the bulb to turn on? Is it half a second, one second, two seconds, 1/c second, or none of the above? You have to make some simplifying assumptions about this circuit, such as that the wires should have no resistance;

Otherwise this would not work and the bulb should light up immediately when current passes through it. But I want you to commit to an answer and write it in the comments so you can't say, oh yeah, I knew that was the answer, when I tell it to you later. This question actually relates to how electrical energy gets from a power plant to your home. Unlike a battery,

electricity

from the grid comes in the form of alternating current, or AC, which means electrons in power lines simply move back and forth. They never really go anywhere. So, if the loads don't come from the power plant to your house, how does the electric power actually get to you?

When I taught this subject, I said that power lines are like this flexible plastic tube and the electrons inside are like this chain. So what a power plant does is push and pull electrons back and forth 60 times per second. Now, in your house, you can plug in a device, like a toaster, which basically means allowing electrons to pass through it. So when the power plant pushes and pulls on the electrons, they encounter resistance in the toasting element and dissipate their energy as heat, so you can toast your bread. This is a great story, I think it's easy to visualize and I think my students understood it.

The only problem is that it's wrong. For one thing, there is no continuous conductor cable running from a power plant to your home. No, there are physical gaps, there are breaks in the line, like in transformers where one coil of wire is wound on one side and a different coil of wire is wound on the other side. Therefore, it is impossible for electrons to flow from each other. Furthermore, if it is electrons that carry energy from the power plant to your device, then when those same electrons return to the power plant, why not also carry energy from your home to the power plant?

If current flow is bidirectional, 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 1870s, a breakthrough in our understanding of the universe occurred when Scottish physicist James Clerk Maxwell realized that light is made up of oscillating electric and magnetic fields. The fields oscillate perpendicular to each other and are in phase, meaning when one is at its maximum, so is the other wave.

Now, he solves the equations that govern the behavior of electric and magnetic fields, and therefore these waves, are now called Maxwell's equations. But in 1883, one of Maxwell's former students, John Henry Poynting, is thinking about the energy conversation. If energy is conserved locally in each small space, then we should be able to trace the path by which energy flows from one place to another. So, let's think about the energy that comes to us from the sun, during those eight minutes that light travels, the energy is stored and transmitted in the electric and magnetic fields of light. Now, Poynting comes up with an equation to describe energy flow, that is, how much electromagnetic energy passes through an area per second.

This is known as a Poynting vector and is given the symbol S. And the formula is actually quite simple, it is simply a constant over mu zero, which is the permeability of free space multiplied by E X B. Now, E X B, is the product crossing of electric and magnetic fields. Now, the cross product is just a particular way of multiplying two vectors, where you multiply their perpendicular magnitudes and to find the direction, you place your fingers in the direction of the first vector, which in this case is the electric field, and rotate them in the direction of the second vector, the magnetic fields, then your thumb points in the direction of the resulting vector, the energy flow.

So what this shows us about light is that energy flows perpendicular to both the electronic and magnetic fields. And it's in the same direction that light travels, so this makes a lot of sense. Light transports energy from its source to its destination. But the interesting thing is this: the Poynting equation doesn't just work for light, it works whenever electric and magnetic fields coincide. Whenever you have electric and magnetic fields together, there is a flow of energy and you can calculate it using the Poynting vector. To illustrate this, let's consider a simple circuit with a battery and a light bulb.

The battery itself has an electric field, but since there are no moving charges, there is no magnetic field, so the battery does not lose energy. When the battery is connected to the circuit, its electric field spreads through the circuit at the speed of light. This electric field pushes electrons so that they accumulate on some of the conductors' surfaces, charging them negatively, and are depleted elsewhere, leaving their surfaces positively charged. These surface charges create a small electric field within the wires, causing the electrons to deflect preferentially in one direction. Note that this drift speed is extremely slow, about a tenth of a millimeter per second.

But this is current, well, conventional current is defined to flow in the opposite direction to the motion of the electrons, but this is what makes this happen. The charge on the surfaces of the conductors also creates an eclectic 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 this space around the circuit. So according to Poynting theory, energy should flow and we can calculate the direction of this energy flow using the right hand rule. Around the battery, for example, the electric field decreases and the magnetic field reaches the screen.

So, you will find that the power flow is to the right of the battery. In fact, around the entire battery, you will find that the power is radially outward. The energy exits the sides of the battery into the fields. Along the wires, again, you can use the right-hand rule to find that the energy flows to the right. This is true for the fields along the top wire and the bottom wire. But in the filament, the Poynting vector is directed toward the bulb. So the light bulb gets energy from the field. If you do the cross product, you will find that the energy comes from all around the bulb.

There are many paths from the battery to the light bulb, but in all cases the energy is transmitted through electric and magnetic fields. - People seem to think that you are pumping electrons and that you are buying electrons or something, which is very wrong. (Laughter) For most people, and I think to this day, it's quite contradictory to think that energy flows through the space around the conductor, but energy that travels through the field, yes, it goes pretty fast. . - So, there are a few things to keep in mind here. Although the electrons move away from and toward the battery in two directions, using the Poynting vector it is discovered that the energy flow only goes in one direction from the battery to the light bulb.

This also shows that it is the fields and not the electrons that carry the energy. - How far do the electrons go in this little thing you talk about? They barely move, probably not move at all. - Now, what happens if instead of a battery we use an alternating current source? Well, the direction of the current is reversed every half cycle. But this means that both the electric and magnetic fields are reversed at the same time, so at any instant the Poynting vector is still pointing 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 can flow from power plants to homes through power lines. Inside the wires, the electrons simply oscillate back and forth. His movement here is very exaggerated. But they do not transport energy. Outside the wires, oscillating magnetic and eclectic fields travel from the power plant to your home. You can use the Poynting vector to check that the energy flow is in one direction. You might think that this is just an academic discussion where you could look at the energy transmitted by fields or by the current in the wire. But that's not the case, and people learned it the hard way when they started laying underwater 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 try to send signals. - Huge amounts of distortion. They could work it at a few words per minute. - What they found was sending signals such a long distance under the sea that the pulses became distorted and elongated. It was difficult to differentiate the dots from the dashes. To explain the failure, there was a debate among scientists. William Thomson, the future Lord Kelvin, thought that electrical signals moved through underwater cables like water flowing through a rubber tube.

But others, such as Heaviside and Fitzgerald, argued that it was the fields around the cables that carried the energy and information. And, ultimately, this opinion turned out to be correct. To insulate and protect the submarine cable, the central copper conductor was coated with an insulator and then enclosed in an iron sheath. The iron was only intended 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. For this reason, most power lines today are suspended overhead. Even moist soil acts as a conductor, so there needs to be a large insulating air gap to separate the wires from the ground.

So what is the answer to our giant circuit light bulb question? Well, after you close the switch, the bulb will turn on almost instantly, in about 1/C of a second. So the correct answer is D. I think many people imagine that the electric field must travel from the battery to the wire, lasting one light second, so it should take one second for the light bulb to turn on. above. But what we've learned in this video is that what really matters is not what happens on the cables, but what happens around the cables. And electric and magnetic fields can propagate through space to this light bulb, which is just one meter away in a few nanoseconds.

And so, that's the limiting factor for the light bulb to come on. Now, the bulb will not receive all the voltage from the battery immediately, it will be a fraction, which depends on the impedance of these lines and the impedance of the bulb. I asked several experts about this question and got different answers, but we all agreed on these main points. So, I'll put his analysis in the description in case you want to learn more about this particular setup. If I get reported and people don't believe it's real, we can definitely invest the resources, lay some lines and build our own power lines in the desert. - I think they're going to sue you for that. - I agree, I think they will catch your attention. (laughing) I think that's true. - I think it's a little crazy that this is one of those things we use every day, where almost no one thinks about or knows the correct answer.

These electromagnetic waves that travel around power lines are actually what supply power. Hey, now that you understand how electrical energy actually flows, you can think about that every time you turn on a light switch. And if you want to take your switches to the next level, the sponsor of this video, Caseta by Lutron, offers premium smart lighting control, including plug-in smart switches, remotes, and dimmers. And since one switch can control many regular light bulbs, you can make all those light bulbs smart just by replacing the switch. You can then turn the lights on and off using your phone, or you can use another device like Alexa or Google Assistant.

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If you need help, you're just a click or call away. Learn more about Caseda on the Lutron website, lutron.com/veritasium. I'll put that link in the description. So, I want to thank Lutron Electronics for sponsoring this video and I want to thank you for watching it.