How Electrical Energy Flows: In the Wire or Around It?

An applied extra to Cobler's Electricity Fundamentals course.

Stand under a high-voltage line on a damp evening and you can hear it: a low buzz coming off the wires, out of the air itself. Nothing is touching the cable. That sound is the field around the conductor, working on the moist air. Most of us walk past without asking, because we think we already know the answer. The electricity is in the wire. It runs through the copper like water through a pipe. Part 1 of this course ended by contradicting that: the electrons crawl, and the energy races outside the wire. How electrical energy flows turns out to have an answer most of us have never been told, and it is cleaner than you would guess.

How electrical energy flows: the one-line answer

Not inside the copper. Electrical energy flows through the electric and magnetic fields in the space around the conductors, and the wire's job is to guide those fields, not to carry the energy inside itself.

The tool physicists use to say exactly where energy is going is the Poynting vector, written \(\vec S = \vec E \times \vec H\), the cross product of the electric and magnetic field at a point. Wherever both fields exist, which is the space wrapped around a live wire, that vector points along the cable and into the load. This is standard, century-old electromagnetism (Poynting published it in 1884), not a fringe reinterpretation. The copper shapes the fields; the fields deliver the power. The electrons inside are still doing the slow forward shuffle we clocked in Part 1, at a fraction of a millimetre per second, but the energy is not riding on their backs.

The thought experiment that broke the internet

In November 2021, Veritasium (Derek Muller) posted "The Big Misconception About Electricity" and set a trap that looked trivial. Take a battery, a switch and a small lamp. Now connect them with a pair of wires so absurdly long that each one runs out a full light-second before coming back, while the lamp itself sits just one metre from the battery. Close the switch. How long before the lamp first lights?

The tempting answers are one second, or half a second, the time a signal would need to crawl down all that wire. Veritasium's answer was about one metre divided by the speed of light, roughly 3.3 nanoseconds. His reasoning: the energy never had to travel the length of the wire at all. It crosses the small gap between the outgoing and returning conductor directly, through the field, because the two wires sit a metre apart right next to the lamp.

The internet detonated.

Was Veritasium right? A fair adjudication

The honest verdict: everyone was right about the piece they chose to emphasise, and the physics left standing is Poynting's. Here is the timeline, with dates, because the argument is often retold unfairly.

ElectroBOOM (Mehdi Sadaghdar), 8 December 2021, replied with "How Wrong Is VERITASIUM? A Lamp and Power Line Story" and pushed hard on a single word: lights. A tiny coupled signal does reach the lamp at 3.3 nanoseconds, but it is a faint whisper of a current, nowhere near enough to make a filament visibly glow. Calling that moment "the lamp lights" oversells it; useful brightness only arrives once the wave has run down the line. His conclusion was generous: wrong on a technicality, but a genuinely great question about how electromagnetic energy moves.

AlphaPhoenix (Brian Haidet) stopped arguing and built it. He laid out roughly a thousand metres of wire, wired in a fast switch, and watched the far end on an oscilloscope. The measurement settled it: the instant the switch closes, a small step appears at the lamp end essentially immediately, coupled straight across the gap through the field. The voltage then climbs in further steps as the wave travels down the line and its reflections arrive and settle, reaching full value only later. Both pictures were real, at different moments.

Veritasium's own follow-up, "How Electricity Actually Works" (5 May 2022), answered the critics and presented the field picture more carefully, leaning less on the provocative "instant" framing.

So: Veritasium was right that a real signal arrives almost instantly through the field, not by electron drift. ElectroBOOM was right that "lit" is doing heavy lifting. AlphaPhoenix measured both truths at once. The Science Asylum (Nick Lucid) laid out the same conclusion from the energy side. Under all of it, one statement survives untouched: conductors are guides, not pipes, and the energy lives in the field.

Why the shape of the cable matters

Because the fields live in the geometry. The spacing between the conductors, their thickness, and the insulator sandwiched between them decide how the fields are shaped, and that fixes a property called characteristic impedance:

$$Z_0 = \sqrt{\frac{L}{C}}$$

Skip the formula if you like, the idea is all that matters. Here L and C are the inductance and capacitance per metre of cable, both set purely by its dimensions. A coaxial cable is 50 ohms not because someone soldered in a resistor but because of its cross-sectional shape. When AlphaPhoenix capped his long line with a 50 ohm resistor, he was matching that impedance so the incoming wave was absorbed cleanly instead of bouncing back and ringing. Deform the geometry and you deform the field guide, which is exactly why a pinched, sharply kinked, or badly terminated cable starts to misbehave at high frequencies.

Why long lines and undersea cables are their own animal

Once a cable is long enough that a signal takes real time to cross it, it stops acting like a plain wire and starts acting like a transmission line: a guided path for an electromagnetic wave, with reflections, timing and impedance all in play. The first transatlantic telegraph cable of 1858 ran into this the hard way, failing within weeks after operators tried to force signals through thousands of kilometres of undersea line with brute voltage rather than respecting the cable's own field behaviour. Every submarine power link and long high-voltage line today, including the HVDC cables from AC vs DC, is engineered as a transmission line first and a lump of copper second. It is the same physics that governs the equations behind the fields, the ones Maxwell decoded into four lines.

Does any of this change your electricity bill?

No. The meter still counts honestly. Whether you picture the joules travelling inside the copper or in the field wrapped around it, the same energy arrives at your load, and your kWh meter integrates the same power over the same time. Poynting's picture is a better mental model, not a loophole. Nothing about tariffs, demand charges or metering shifts by a single cent because the energy rides outside the wire.

What does change is how you see the everyday thing. Next time you hear that buzz under a power line, you will know the sound is not leaking out of a full pipe. It is the field doing the actual work of carrying the energy, out in the air, with the copper serving as nothing more than the rail it follows.

Go deeper on video

Reading explains; watching sometimes lands the picture. Full credit to the creators:

This is an applied extra to Cobler's Electricity Fundamentals course. It sits closest to Part 1, what electricity actually is, which first slipped in the idea that the energy travels outside the wire, and to Maxwell's equations decoded, the four laws that describe the very fields doing the carrying.

None of this shows up on an invoice, but seeing your building's energy clearly still does. CobiNeural meters real power, demand and power quality across a whole site, so the joules you pay for stop being invisible. If you would rather see your electricity than take it on faith, talk to us.