The Big Misconception About Electricity

Summary

In this enlightening video, sponsored by Caséta by Lutron, the misconceptions about how electricity travels are debunked. The video explains that it's not the electrons but the oscillating electric and magnetic fields that transmit energy, as demonstrated by Maxwell's and Poynting's equations. This concept clarifies how power reaches homes through AC power lines, despite electrons oscillating within the wires. The video also addresses the historical challenges with undersea telegraph cables and highlights the importance of understanding electromagnetic fields in modern electrical systems. With a touch of humor, the host invites viewers to rethink their knowledge of electricity every time they flip a switch, while promoting Caséta's smart lighting solutions.

Takeaways

• 🔌 Sponsored Content: The video was sponsored by Caséta by Lutron, a company that provides smart lighting control solutions.
• 🌐 The Giant Circuit Hypothesis: The video begins with a thought experiment involving a giant circuit with wires as long as the distance light travels in a second, to illustrate how electricity works.
• 💡 Light Bulb Question: The central question posed is how long it would take for a light bulb to light up after closing a switch in the described giant circuit.
• ⚡ Simplified Assumptions: The thought experiment requires assuming no resistance in the wires and an immediate reaction from the light bulb to the flow of current.
• 🔍 Misconceptions About Electricity: The video addresses common misconceptions about how electricity travels, such as the belief that electrons carry energy from the power plant to the home.
• 🔄 Alternating Current (AC): The video explains that electricity in the grid comes in the form of AC, where electrons wiggle back and forth without actually moving from the power plant to the home.
• 🌐 Maxwell's Equations: The video introduces James Clerk Maxwell's equations, which describe how electric and magnetic fields oscillate and are in phase with each other.
• 📈 Poynting Vector: John Henry Poynting's work is highlighted, introducing the Poynting vector (S), which describes the flow of electromagnetic energy.
• 🚀 Energy Flow Through Fields: The video clarifies that it is the electric and magnetic fields, not the electrons themselves, that carry energy in a circuit.
• 🌊 Undersea Telegraph Cables: Historical context is provided about the challenges faced with undersea telegraph cables, which led to a better understanding of how electromagnetic fields propagate.
• 🏡 Power Lines and Energy Transmission: The video concludes by explaining that energy flows from power plants to homes through oscillating electric and magnetic fields, not through the physical movement of electrons.
• 🛠 Practical Application: The video connects the theoretical discussion to practical applications, such as the design of power lines and the function of smart lighting systems like those offered by Caséta by Lutron.

Q & A

What is the key question posed at the beginning of the video?

The key question is how long it would take for a light bulb to light up after closing a switch in a circuit with two wires each 300,000 kilometers long.

What are the simplifying assumptions made about the circuit in the video?

The assumptions are that the wires have no resistance and the light bulb turns on immediately when current passes through it.

How does alternating current (AC) differ from direct current (DC) in terms of electron movement?

In AC, electrons in the power lines wiggle back and forth without actually traveling long distances, whereas in DC, electrons flow in a single direction from the power source to the load.

Why is the analogy of electrons moving like water through a hose incorrect for describing electricity transmission?

The analogy is incorrect because there are breaks in the physical wire, such as in transformers, preventing a continuous flow of electrons. Moreover, the energy transfer happens through electromagnetic fields, not by the physical movement of electrons over long distances.

What significant breakthrough did James Clerk Maxwell achieve in the 1860s and 70s?

James Clerk Maxwell realized that light is made up of oscillating electric and magnetic fields, and he developed equations to describe their behavior, now known as Maxwell's equations.

What is the Poynting vector and what does it describe?

The Poynting vector, denoted as S, describes the energy flux or how much electromagnetic energy is passing through an area per second. It is calculated using the formula S = (1/mu_0) * (E x B), where E is the electric field and B is the magnetic field.

How does energy flow from a battery to a light bulb in a simple circuit according to the Poynting vector?

Energy flows through the electric and magnetic fields surrounding the wires and the battery. The Poynting vector indicates that energy radiates out from the battery into the fields and flows along the wires towards the light bulb.

Why do electrons not carry the energy from a power station to a home in an AC power grid?

Electrons in AC power grids oscillate back and forth and do not travel significant distances. The energy is carried by oscillating electric and magnetic fields in the space around the wires.

What issue did early submarine telegraph cables face, and what was the underlying cause?

Early submarine telegraph cables faced signal distortions and lengthening of pulses, making it hard to differentiate dots from dashes in Morse code. This was caused by the increased capacitance due to the iron sheath around the cables, which interfered with the propagation of electromagnetic fields.

What happens to the light bulb in the giant circuit after the switch is closed?

The light bulb will turn on almost instantaneously, in roughly 1/C seconds. This is because the electric and magnetic fields can propagate through space to the light bulb, which is only one meter away, in a few nanoseconds.

Outlines

00:00

🔌 The Mystery of Electrical Energy Transmission

This paragraph introduces a thought experiment involving a giant circuit with a battery, a switch, a light bulb, and extremely long wires to illustrate the speed at which electricity travels. It challenges the viewer to think about how long it would take for the bulb to light up after the switch is closed. The discussion transitions into how electricity is transmitted in the form of alternating current (AC) through power lines, using a misconception about electrons moving from the power plant to homes. The paragraph debunks this idea and introduces the concept that electrical energy is transmitted through oscillating electric and magnetic fields, not through the physical movement of electrons.

05:02

🌐 The Role of Electromagnetic Fields in Energy Transfer

The paragraph delves into the scientific breakthroughs by James Clerk Maxwell and John Henry Poynting, who described how light, composed of oscillating electric and magnetic fields, carries energy. Poynting's vector is introduced as a formula to calculate the flow of electromagnetic energy. The explanation is applied to a simple circuit with a battery and a light bulb, showing how energy flows through the space around the conductors via electric and magnetic fields, rather than through the electrons themselves. The paragraph clarifies that it's the fields that carry the energy, unidirectional from the source to the device, and this principle applies to both direct current (DC) and alternating current (AC).

10:02

⚡ The History of Undersea Cables and Energy Flow

This paragraph discusses the historical challenges faced with the first Transatlantic telegraph cable and the scientific debate around signal transmission. It highlights the incorrect assumption that signals moved through the cable like water in a tube and the correct understanding that electromagnetic fields around the wires carried the energy and information. The discussion emphasizes the importance of minimizing interference with these fields for effective energy transmission. The paragraph concludes with the resolution of the initial thought experiment, explaining that the light bulb would turn on almost instantly when the switch is closed due to the rapid propagation of electric and magnetic fields, not because of electron flow along the wires.

🏠 Practical Applications and Smart Lighting Innovations

The final paragraph shifts focus to the practical applications of electricity in everyday life, specifically mentioning the sponsor of the video, Caséta by Lutron. It discusses the convenience and innovation of smart lighting controls, which allow for advanced functionalities such as remote operation, timers, and integration with other smart home systems. The ease of installation and the benefits of smart switches in enhancing home lighting are highlighted, with an invitation for viewers to learn more about Caséta's products and to reflect on the underlying principles of electrical energy transmission every time they use a light switch.

Keywords

💡Caséta by Lutron

Caséta by Lutron is a smart lighting control system that is mentioned as the sponsor of the video. It provides advanced control over lighting in a home or building, allowing users to adjust settings remotely or automate them for convenience and energy efficiency. In the context of the video, Caséta by Lutron is used to introduce the topic of electrical energy and its transmission, setting the stage for the discussion on how electricity works and the common misconceptions about it.

💡Electrical Circuit

An electrical circuit is a closed loop through which electric current flows. It is composed of a power source (like a battery), electrical devices (like a light bulb), and conductive paths (wires) that connect them. In the video, a hypothetical giant circuit is used to illustrate the speed at which electrical signals travel, emphasizing the role of wires and switches in the process of electricity transmission.

💡Alternating Current (AC)

Alternating Current (AC) is a type of electrical current where the flow of electric charge periodically reverses direction. Unlike direct current (DC), where the flow of electrons is in one direction, AC is the form of electrical energy that is most commonly used in power grids. The video explains that AC involves electrons 'wiggling back and forth' in the power lines, which is a key concept in understanding how electrical energy is transmitted over long distances without the electrons themselves traveling the entire distance.

💡Maxwell's Equations

Maxwell's Equations are a set of four fundamental equations that describe the behavior of electric and magnetic fields. These equations, formulated by James Clerk Maxwell in the 19th century, are crucial to understanding how light, which is an electromagnetic wave, behaves. In the video, Maxwell's Equations are referenced to explain that light is made up of oscillating electric and magnetic fields, which is a foundational concept for the discussion on how energy is transmitted through electromagnetic fields.

💡Poynting Vector

The Poynting Vector, named after John Henry Poynting, is a concept used to describe the direction and rate at which electromagnetic energy is transmitted through space. It is represented by the cross product of the electric and magnetic fields (E X B) and shows that energy flows perpendicular to both fields. In the video, the Poynting Vector is used to demonstrate that energy in an electrical circuit flows through the space around the wires, not just through the wires themselves, which is a critical insight into the actual mechanism of energy transmission in electrical systems.

💡Energy Flux

Energy flux refers to the amount of energy that passes through a unit area per unit time. It is a measure of the rate at which energy is transferred across a surface. In the context of the video, energy flux is explained through the Poynting Vector, showing that in an electrical circuit, energy is transferred through the electromagnetic fields around the wires, not just by the movement of electrons within the wires.

💡Electromagnetic Fields

Electromagnetic fields are produced by electrical charges and their motion. They are invisible forces that can exert forces on other charges and are fundamental to the operation of many electrical devices and systems. The video emphasizes that it is the oscillating electromagnetic fields, not the flow of electrons, that transmit energy in electrical circuits and power lines, which is a key point in correcting common misconceptions about electricity.

💡Impedance

Impedance is a measure of how much a device in an AC circuit resists or impedes the flow of electrical current. It is a complex quantity that combines both resistance and reactance (which includes capacitive and inductive effects). In the video, impedance is mentioned in relation to the fraction of voltage that a light bulb would receive immediately after a switch is closed, indicating that the full voltage is not instantly transferred due to the impedance of the circuit and the bulb.

💡Undersea Telegraph Cables

Undersea telegraph cables were the first means of long-distance communication across oceans, transmitting information via electrical signals. The video references the historical challenges faced with these cables, such as signal distortion over long distances. This historical context serves to illustrate the importance of understanding the transmission of electrical signals and energy, not just through wires, but also through the surrounding electromagnetic fields.

💡Smart Lighting Control

Smart lighting control refers to systems that allow for the remote or automated control of lighting in a home or building. These systems can offer energy savings, convenience, and enhanced security. In the video, smart lighting control is mentioned in the context of Caséta by Lutron, which is the sponsor of the video. The system allows users to control lights through switches, remotes, and even through integration with other smart home devices like Alexa or Google Assistant.

💡Electric Field

An electric field is a region around an electrically charged particle or object within which a force would be experienced by other charged particles. In the video, the electric field is discussed in the context of how it extends through a circuit at the speed of light when the circuit is closed, influencing the movement of electrons and the subsequent creation of a magnetic field. The interaction of electric fields with magnetic fields is central to the video's explanation of how energy is transmitted in an electrical circuit.

Highlights

The video discusses the misconceptions about how electricity works and introduces the concept of electromagnetic fields as the carriers of electrical energy.

A thought experiment involving a giant circuit with wires as long as the distance light travels in a second is presented to illustrate the speed at which electrical energy propagates.

The video explains that in AC power systems, electrons do not travel from the power plant to homes but rather oscillate back and forth, contrary to common belief.

James Clerk Maxwell's equations and the concept of light as oscillating electric and magnetic fields are introduced to explain the propagation of electromagnetic waves.

John Henry Poynting's work on energy conservation and the Poynting vector, which describes the flow of electromagnetic energy, is discussed.

The Poynting vector formula, E X B, is explained, showing that energy flows perpendicular to both electric and magnetic fields.

The video uses the right-hand rule to demonstrate the direction of energy flow in electrical circuits, highlighting that energy comes from the fields, not the electrons.

It is clarified that the energy in a circuit flows from the battery to the light bulb through the electric and magnetic fields, not through the movement of electrons.

The video addresses the failure of early undersea telegraph cables and the debate among scientists about the propagation of signals, leading to the understanding that fields around wires carry energy.

The importance of insulating power lines with air gaps to prevent interference with electromagnetic field propagation is explained.

The answer to the giant circuit light bulb question is revealed, showing that the light bulb turns on almost instantaneously due to the speed of electromagnetic fields.

The video emphasizes that it is the electric and magnetic fields, not the electrons, that carry the energy in both DC and AC systems.

Caseta by Lutron is introduced as a sponsor, offering smart lighting control systems that can upgrade traditional switches and bulbs to smart technology.

The video showcases the practical applications of smart switches, such as timers and remote control via phones or voice assistants, provided by Caseta by Lutron.

Easy installation of Caseta smart switches is highlighted, with support available from Lutron for any assistance needed.

A call to action is made for viewers to learn more about Caseta by visiting Lutron's website, with a link provided in the video description.

Transcripts

This video was sponsored by Caséta 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 kilometers long.

That is the distance light travels in one second.

So, they would reach out half way 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

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

get from a power plant to your home.

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 wire is wrapped on one side,

a different coil of wire is wrapped on the other side.

So, electrons cannot possibly flow

from one 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 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 1860's and 70's,

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 conversation of energy.

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,

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 one over mu naught,

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 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 fields,

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 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 a flow of energy

and you can calculate 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 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'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.

- 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 quite counterintuitive

to think that the energy is flowing through the space

around the conductor,

but the energy 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,

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.

- 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 home 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 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 the hard way

when they started laying undersea telegraph cables.

The first Trans Atlantic 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.

- 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 a 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.

But 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 one 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 gonna put their analysis in the description

in case you want to learn more about this particular setup.

If I get called out on it

and people don't think it's real,

we can definitely invest the resources

and string up some lines,

and make our own power lines in the desert.

- I think you're gonna get called out on it.

- I agree, I think you're gonna get called out.

(laughing)

I think that's right.

- I think it's just kinda wild

that this is one of those things

that we use everyday,

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,

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or you can use another device

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One of the things I like is setting timers.

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And this feature gives you peace of mind

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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

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Make sure you turn off power to the switch first

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If you need any help,

they're just a click or a call away.

Learn more about Caseda 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.