La idea errónea que nos enseñan sobre la electricidad

Imagine you have a giant circuit consisting of a battery, an interrupter, a bulb and two cables of 300,000 kilometers each. That's the distance that light travels in a second. They would cover half the distance to the moon, back and forth, to connect to the bulb that is a meter away. The question is: after turning off the switch, how long will the bulb take to turn on?

half a second, one second, two seconds, one over six seconds, or none of those. You should take for granted some things that simplify it, such as that the cables should not have resistance, or this would not work, and that the bulb turns on the moment the current crosses it. But I want you to commit to an answer and put it in the comments so that you can't say "Yes, I knew that was the answer" when I tell you later.

This question is related to how the electrical energy comes from the power plant to your home. Unlike a battery, the electricity in the network comes in the form of alternating current, that is, which means that the electrons in the cables move forward and backward, they never go anywhere. So if the charges do not come from the power plant to your home, how does the electrical energy get to your home?

When I was teaching about this, I used to say that the cables are like this flexible plastic tube and that the electrons inside are like this chain. What the power plant does is push and pull the electrons back and forth 60 times per second. In your house, you can plug something like a toaster, which means that you allow the electrons to pass through it.

So when the power plant pushes and pulls the electrons, they find resistance in the toaster and dissipate their energy like heat and you can toast your bread. This is very cool, it's easy to see and I think my students understood it. But there is a problem. It's incorrect.

First of all, there is no continuous cable that goes directly from the power plant to your home. No. There are physical gaps, there are cracks in the line, like in the transformers, where there is a cable coil on one side and another coil on the other side, and so the electrons cannot flow from one to the other. Also, if it is the electrons that carry the power from the power plant to your device,

When those same electrons flow to the central, why don't they carry energy back from your house to the central? That is, if the current flows in both directions,

Why does energy only flow in one direction? These are the lies that were taught to you about electricity. That the electrons themselves have potential energy. That they are pushed or attracted in a continuous loop and that they dissipate their energy in the devices. In this video, I propose that all of that is false. So how does it really work?

In the 1860s and 70s there were great advances to understand the universe when the Scottish physicist James Clerk Maxwell discovered that light is made of oscillating electric and magnetic fields. Those fields oscillate perpendicularly between them and are in phase, so if one is at its maximum, so is the other.

He made the equations that govern the behavior of electric and magnetic fields, and therefore these waves. Today they are called Maxwell's equations. But in 1883, one of Maxwell's disciples, John Henry Poynting, begins to think about the conservation of energy. If energy is locally preserved in every corner of space, you should be able to track the path through which energy flows from one place to another.

Think of the energy that comes to us from the sun. During those eight minutes in which the light travels, the energy is stored and transmitted in the electric and magnetic fields of the light. Poynting creates an equation that describes the flow of energy, that is, how much electromagnetic energy passes through a certain area per second.

This is known as the pointing vector and is given the symbol S. The formula is quite simple. It is a constant, 1/ , which is the permeability of the vacuum, multiplied by the cross product of E/B. This is the vector product of the electric and magnetic fields.

The cross product is a particular way of multiplying two vectors with each other, where you multiply their perpendicular magnitudes and to find the direction you put your fingers in the direction of the first vector, in this case it is the electric field, and the curves in the direction of the second vector, the magnetic fields, and your thumb points in the direction of the resulting vector, the energy flow. What this shows us about light

is that energy flows perpendicularly to magnetic and electrical fields and it is in the same direction in which light travels, which makes a lot of sense. Light carries energy from its source to its destination. But the key is this:

The Pointing equation not only works for light, it works every time electric and magnetic fields coincide. Whenever there are electric and magnetic fields together, there is a flow of energy and you can calculate it using the Pointing vector. To illustrate this, let's see a simple circuit with a battery and a bulb.

The battery itself has an electric field, but since the charges don't move, there is no magnetic field, so the battery doesn't lose energy.

When the battery is connected to the circuit, its electric field extends through that circuit at the speed of light. This electric field pushes electrons that accumulate on some surfaces of the conductors, generating negative charges and reducing them in others, leaving those surfaces with positive charge.

These loads on the surfaces create a small electric field inside the cables, causing the electrons to travel preferably in one direction. The speed at which they travel is very slow, around a tenth of a millimeter per second. But this is the current. Well, conventional current by definition flows contrary to the direction of the electrons, but I'll tell you how this happens.

The load on the surface of the conductors also creates an electric field outside the cables, and the current inside the cables creates a magnetic field outside them. Now there is a combination of electric and magnetic fields in space around the circuit.

According to the Pointing theory, there should be a flow of energy, and we can determine the direction of this flow using the rule of the right hand. Around the battery, the electric field is down and the magnetic field in the screen. So you have the energy flowing outwards and to the right of the battery. In fact, around the battery you have the energy is radial outwards.

The energy goes out, on the sides of the battery, towards the fields. Through the cables, you can also use the same rule and find that the energy flows to the right. This happens in the fields around the upper cable and the lower cable. But in the filament, the pointing vector points inwards of the bulb.

People usually think that you pump electrons, that you buy electrons or something like that. They're very wrong.

For many people, today it is very counterintuitive to think that energy flows in the space around the driver. But the energy that travels through the field does it quite quickly.

There are several things to observe here. Although the electrons go in two directions, outwards from the battery and towards it, when using the Poynting vector, you find that the energy flows only in one direction, from the battery to the bulb. This also shows that it is the fields and not the electrons that carry the energy. How many electrons move in the scheme you are proposing? Almost nothing, maybe they don't move.

What happens if, instead of a battery, we use a power source? The direction of the current is reversed every half cycle. This means that both the electric and magnetic fields are reversed at the same time. So, at all times, the Pointing vector continues to point in the same direction, from the source to the bulb. The same analysis that we use with the continuous current works with the alternating current.

And this explains how energy can flow from the power plants to homes by the electrical wire. Inside the cables, the electrons move back and forth. Here you can see it exaggeratedly. But they don't carry the energy. Outside the cables, the oscillating electric and magnetic fields travel from the power plant to your home. You can use the Poynting vector to see that the energy flow goes in one direction.

You might think that this is just an academic discussion, that you can think of energy as transmitted by fields or by the current of the cable. But that's not the case. And people learned it in a difficult way when they placed submarine telegraph cables. The first transatlantic cable was placed in 1858. It only worked for a month, it never worked well. There are all kinds of distortions when sending signals. Huge distortions. They could use it in a couple of words per minute.

They found that, by sending signals so far under the sea, the pulses were distorted and elongated. It was difficult to differentiate the points of the lines.

To explain these failures, there was a debate among scientists. William Thompson, the future Lord Kelvin, believed that electrical signals through underwater cables were like water flowing in a rubber tube. But others, like Heaviside and Fitzgerald, said that it was the fields around the cables that moved the energy and information. And finally, it was proven that it was true.

To isolate and protect the submarine cable, the central copper conductor was covered by an insulator and inserted into an iron cover.

Iron intended to strengthen the cable, but as a good conductor, it interfered with the propagation of electromagnetic fields, because it increased the cable capacity. For this reason, today most of the cables are suspended at high speed. Even wet earth works like a conductor. So it is better to have a large space of air that isolates the cables from the ground. So what is the answer to the question about the giant circuit with the bulb?

After pressing the switch, the bulb will turn on almost immediately. In about 1/6 seconds. The correct answer is D.

I think a lot of people imagine that the electric field needs to travel from the battery through the cable of a second long light, so it should take a second to turn on. But what we have learned is that what matters is not what happens in the cables, it is what happens around it.

And the electric and magnetic fields can spread in space up to the bulb that is a meter in nanoseconds. And that is the limiting factor for it to turn on. Now, the bulb will not receive the full voltage of the battery immediately, it will be a fraction that depends on the impedance of the cables and the bulb.

I asked several experts about this and got different answers, but they all coincided in these key points. I will put their analyzes in the description in case you want to know more about this particular scheme. If you don't believe me and people think it's not true, we can definitely invest and build the installation, make our cable in the desert.

I think it's strange that this is one of those things we use every day and about which almost no one thinks or knows the answer. The electromagnetic waves that travel around the cables are the ones that really bring your energy.