- How fast can electricity travel?

(thunder booming) Well, one guy decided the best way to find out was to shock a bunch of monks.

In 1746, (bells chiming) a French abbot and physicist named Jean-Antoine Nollet arranged a large group of monks and connected them by thick wires.

His plan was to measure the speed of electricity as the monks were electrocuted one by one.

So he was shocked when everyone got electrocuted at the same time.

Nollet concluded that electricity must move with infinite speed.

Of course, nothing moves that fast, but electricity does move really, really fast.

Nollet saw it, the monks felt it, (electricity zapping) and we experience it too anytime we flip a light switch on and the lights come on immediately.

So, what actually happened when Nollet shocked those monks?

And how did we figure it all out?

(bright music) Back in the seventeen and eighteen hundreds, the scientific atmosphere was electric.

Nollet was far from the only one experimenting with electricity.

Actually, he wasn't even the only one electrocuting large groups of people.

(electricity humming) All kinds of scientists, including Charles Francois de Cisternay du Fay, Benjamin Franklin, and Alessandro Volta, were studying lightning and static, observing sparks, experimenting with batteries, and trying to figure out what exactly electricity was and how it moved.

And at the time, people mostly thought of electricity as fluid.

Nollet even got in a fight with Franklin about whether electricity is made up of one or two fluids.

Neither one was right, but it would take a few more decades to figure that out.

Things really took off in 1831 when Michael Faraday used a battery to discover electromagnetic induction.

He showed that magnets in motion could create an electric current in a loop of wire, uncovering an important connection between electricity and magnetism.

Then in the 1850s, the Scottish physicist and mathematician James Clerk Maxwell looked at Faraday's experimental results and theories about electricity and magnetism, and he wrote mathematical equations that describe the observations.

He ended up with a set of equations, now called Maxwell's equations, which described the relationship between electric and magnetic fields.

Basically, a moving magnetic field creates an electric field and a moving electric field creates a magnetic field.

By the 1860s, Maxwell's work culminated in the theory of electromagnetism, the idea that a magnetic field can produce an electric field, which can produce a magnetic field, and so on.

This cycle creates a whole spectrum of waves of energy at different frequencies.

Everything from radio waves to visible light to gamma rays that we later identified and harnessed to use in things like radios and Wi-Fi.

Maxwell's theory, more than 100 years after the experiment with the monks, finally revealed the answer to Nollet's question.

In a vacuum, electromagnetic waves move at the speed of light because light waves are, in fact, electromagnetic waves.

So the speed of electricity isn't infinite, but it is just about the fastest thing we know of.

But what does that actually look like?

Well, as Joseph John Thomson helped figure out in the 1890s, electricity isn't fluid.

It's the movement of particles called electrons.

But it's not the electrons themselves that are moving so quickly.

In conductors, which are materials that allow electric currents to flow through them, there are free electrons, or electrons that can jump from one atom to another.

And they move at what's called the Fermi velocity, which depends on the amount of energy the individual particles have.

For copper, which many electrical wires are made from, the Fermi velocity is about 3.5 million miles an hour.

That is really fast.

But this motion happens randomly.

The electrons zip along in straight lines until they bump into other stuff, which happens pretty often.

(pinball clinking) Basically, they're pinging around like pinballs, moving super fast but not very far.

When a voltage is applied to the wire, it creates an electric field that puts a force on the free electrons.

They still move randomly at the Fermi velocity, but now they also get pushed by the electric field at the drift velocity.

But that doesn't explain how your lights turn on when you flip a switch because the net drift velocity depends on the size of the wire.

And it's usually only something like a couple millimeters per second.

At the drift velocity, it would've taken hours for all of Nollet's monks to be electrocuted.

So what we're really talking about is signal velocity.

And that works a lot like a bunch of really impatient people in line for the bathroom.

Say someone at the back of the line bumps into the person in front of them, who bumps into the person in front of them, and so on.

The person at the back of the line doesn't actually move much closer to the bathroom, but their action quickly reaches the bathroom door.

That's how electricity works too.

See, there's a lot of stuff inside a wire, so the electrons keep bumping into other particles.

And when an electric field makes the electrons start drifting, they've gotta push on all the other electrons ahead of them in the line.

That force reaches the other end of the wire almost instantaneously.

In fact, in copper, the signal velocity is nearly 671 million miles an hour, (air whooshes) AKA the speed of light.

So that's how all the monks in Nollet's experiment got electrocuted at the same time and how your lights turn on as soon as you flip the switch.

And in the end, (stopwatch ticking) he was onto something.

Electricity does move fast, just not infinitely fast.

(electricity zapping) But fast enough to light up our world and those monks.

(lighthearted electronic music)