Real Misconception About Electricity

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Real Misconception About Electricity

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 reach out halfway to the moon and then come back to be connected to the light bulb, which is one 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? You have to make some simplifying assumptions. 

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 This circuit, like the wires, has to have no resistance. Otherwise, this wouldn’t work, and the light bulb has to turn on immediately when the current passes through it. But I would be grateful if you could 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 relates to how electrical energy get from a

Power plant to your home. Unlike a battery, the 

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 In the grid comes in 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 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 so that 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 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 wire is wrapped on one side, a different coil of wire is surrounded on the other side. So, electrons cannot possibly flow from one to the other. Plus, 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? If the current flow is in two ways, then why does energy only flow in one direction? These are the lies you were taught. 

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Electrons themselves have the potential energy to push or pull through a continuous conducting loop and dissipate their significance in the device. My claim in this video is that all.

Of that is false. So, how does it work? In the 1860s and ’70s, there was a massive breakthrough in our understanding of the universe when Scottish physicist James Clerk Maxwell realized that light is composed 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 are now called Maxwell’s equations. But in 1883, one of Maxwell’s former students, John Henry Poynting, is thinking. 

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 Conversation of energy. If energy is conserved locally in every tiny bit of space, well, you should be able to trace the path that power flows from one place to another. So, think 

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energy comes from the sun to earth, during those eight minutes when the light is traveling, the power is stored and is transmitted in the

Electric and magnetic fields of 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 pretty simple. It’s just a constant one over mu zero, which is the permeability of free space times E X B. Now, E X B is the cross product of the electric and magnetic fields. Now, the cross product is just a

A particular way of multiplying two vectors together, where you multiply their 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 fields, then your thumb points in the direction of the resulting vector, the energy flux. So, what this shows us. 

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 light is that the energy is flowing perpendicular to both the electronic an 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 energy flow, and you can calculate using Poynting’s vector. The bombardment has an electric field, but there is no magnetic field since no charges are moving, so the battery doesn’t lose energy. The battery is connected to the circuit. Its electric field extends through the course 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 characters 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 eclectic field outside the wires.

 

time lapse photography of square containers at night

 

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’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 on the screen. So, you find the energy flux is to the right away from the battery. All around the battery, you’ll

Find the energy is radially outwards. Power is going out through the sides of the battery into the fields. Again, you can use the right-hand rule to find the energy is flowing to the right along the wires. It’s true for the areas along the top wire and the bottom wire. But at the filament, the Poynting vector is directed toward the light bulb. So, the light bulb is getting energy from the field. If you do the cross product, you find the point is coming in from all around the bulb. – People seem to think that you’re pumping electrons and that you’re buying electrons or something, which is just so wrong. (laughs) For most people, and I think to this day, it’s pretty counterintuitive to think that the energy is flowing through the space around the conductor, but the power is, which is traveling through the field, yeah, is going quite

Fast. – So, there are a few things to notice here. Even though the electrons go two ways away from the battery and towards it, using the Poynting vector, you find that the energy flux only goes one course from the battery to the bulb. also shows it’s the fields and not the electrons that carry the energy. – How far do the electrons go in this little thing you’re talking 

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, 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 it means that both the electric and magnetic fields flip simultaneously, so, at any instant, the Poynting vector still points in the same direction, from the source to the bulb. So the same analysis we used for DC still works for AC. And this explains how energy can flow from power plants to homes in power lines. Inside the wires, electrons oscillate back and forth. Their motion

But they do not carry the energy. Outside the wires, oscillating eclectic 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 hard when they started lying undersea.

Telegraph cables. who are laid the first Trans Atlantic cable in 1858? – It only worked for 

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 a month, it never worked correctly. – There are all kinds of distortions when they try to send signals. – Enormous amounts of distortion. They could work it at a few words per minute. They found that signals over such a long distance under the sea, the pulses became distorted and lengthened. It was hard to differentiate dots from dashes. for the failure, there was a debate among

Scientists. The future Lord Kelvin, William Thomson, thought electrical signals moved through submarine cables like water flowing through a rubber tube. But others like Heaviside and Fitzgerald argued that the fields around the wires carried the energy and information. And ultimately, this view proved correct. 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, interfered with the propagation of electromagnetic fields because it increased the capacitance of the line. The why today, most power lines are suspended high up. Even the damp earth acts as a conductor, so you want a sizeable insulating air gap to separate the wires from the ground. So, what is the answer to our big 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 many people imagine that the electric field needs to travel from the battery down the wire, which is a light second long, so it should take a second for the bulb to light up. But what we’ve learned in this video is it’s not really what’s happening in the wires that matter. It’s what happens around the cables. And the electric and magnetic fields can propagate out through space to this light bulb, which is only one meter away in

A few nanoseconds. The light bulb is 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. 

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 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 if you want to learn more.

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 this

Particular setup. If I get called out on it, and people don’t think it’s real, we can invest the resources, string up some lines, and take our power lines in the desert. – I think you’re going to get called out on it. – I agree. I think you’re going to get called out. (laughing) I think that’s right. – I think it’s just somewhat wild that this is one of those things that we use every day, that almost nobody thinks 

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 Or knows the correct answer? These traveling

Electromagnetic waves around power lines are what’s delivering your power. Hey, now that you understand how electrical energy flows, you can think. 

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 That every time you flick on a light switch. And if you want to take your buttons to the next level, the sponsor of this video, Caseta by Lutron, provides premium intelligent lighting control, including switches, remotes, and plug-in smart dimmers. And since one controller can control many regular bulbs, you can effectively make all.

Those bulbs bright just by replacing the switch. Caseta works with more leading innovative home brands than any other intelligent 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 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 the power to the switch first and then disconnect the existing wires and connect Caseda’s intelligent controller. If you need any help, they’re just a click or a call away. Learn more 

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 Casada 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.

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