What Is Electricity, Actually?

Part 1 of 23 in Cobler's Electricity Fundamentals series. New here? Start with the course map.

You flick the switch and the light is on before your finger has left the plate. It feels instant, and it very nearly is. But the thing you just set moving, the actual particles inside the copper, are crawling. At the current an office light draws, an electron that entered the wire tonight might not reach the bulb by the time you get to work tomorrow. Both of those facts are true at the same time. Holding them together in your head is most of what it means to understand what electricity actually is.

What is electricity, actually?

Electricity is the movement of electric charge, and charge is a basic property of matter, as real as mass. Every atom is a small nucleus of positive charge with negative electrons around it. Normally the two balance and the atom is neutral. Electricity happens when charge gets separated or set flowing.

In a metal, something special is going on. The outermost electrons of each atom are not tied to any single atom. They wander freely through the whole block of metal, a shared sea of loose charge drifting between the fixed atoms. Copper carries roughly 8.5 x 10^28 of these free electrons in every cubic metre ([OpenStax University Physics](https://phys.libretexts.org/Bookshelves/University_Physics/University_Physics_(OpenStax)/University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_(OpenStax)/09:_Current_and_Resistance/9.03:_Model_of_Conduction_in_Metals)). That free sea is exactly what makes a metal a conductor. Give the electrons a push and they can all shuffle along together. That collective shuffle is an electric current.

Why is copper a conductor and rubber is not?

Because in copper the electrons are free to move, and in rubber they are locked in place. That single difference is the whole distinction between a wire and its insulation.

In rubber, PVC, glass and dry air, the electrons stay bound to their atoms. There is no free sea for them to join. Push on them however you like at ordinary voltages and almost nothing flows, which is precisely why we sheath cables in PVC and stand on rubber-soled boots. An insulator is not a material that has no electrons. It is a material whose electrons will not leave home.

This is why the same copper cable does two opposite jobs at once. The metal core invites current to flow. The plastic jacket a millimetre away forbids it. The current runs down the copper and stays there, guided by the insulation, instead of leaking into your hand.

How fast do the electrons actually move?

Slowly. Absurdly, almost comically slowly. In a normal household wire the electrons drift along at a fraction of a millimetre per second.

Work it out and the number is stubborn. Push a couple of amps through an ordinary 1.5 mm2 copper wire and the electron sea drifts forward at around 0.1 millimetre per second (drift velocity, Wikipedia). At that pace an electron takes the better part of three hours to travel a single metre. The charger by your bed tonight is drawing charge that entered the wire hours ago, from somewhere back down the cable, and the electrons currently at the plug will still be dawdling toward it long after you have fallen asleep.

Underneath, individual electrons are actually screaming around at over a million metres per second, a quantum effect of how they pack into a metal rather than literal heat, bouncing off atoms in every direction. But with no push applied, all that motion averages to nothing. Apply a push and you add the faintest forward lean to the chaos. That tiny net lean, riding on top of the violent random jiggle, is the drift. It is the whole of the current.

So why does the light come on instantly?

Because the electrons are not what carries the energy. The energy travels as an electromagnetic wave in the space around the wire, and that wave moves at a large fraction of the speed of light, well over half of it in a normal cable (speed of electricity, Wikipedia). The wire does not carry the energy so much as guide it.

The old picture for this is a tube packed end to end with marbles. Push one marble in at your end and a marble drops out the far end almost the instant you push, even though no single marble travelled the length of the tube. Each one nudged its neighbour and barely moved. The push raced through; the marbles crawled. A wire is that tube, the electrons are the marbles, and the "click" of the switch is the push arriving at the bulb near light speed while the electrons themselves have hardly budged. This is why the popular line about electrons flying from the power station to your house at the speed of light is simply wrong. The signal flies. The electrons crawl.

Static and current: two forms of the same thing

There are really two ways to meet electricity. One is charge that has piled up and gone nowhere. The other is charge in continuous flow.

Rub a balloon on your hair or scuff across a nylon carpet and you strip electrons off one surface onto another. Now one thing is short of electrons and another has a surplus, and that separated charge just sits there as a building pressure. That is static electricity. It stays put until it finds a path, and then it jumps all at once: the little snap off a car door, a spark to a metal handle.

Air is an insulator, but only up to a point. Push the electrical pressure hard enough and even air gives way. It breaks down and turns briefly conductive at a field of roughly 3 kilovolts per millimetre (dielectric strength). That is what a spark is: air losing the argument. Lightning is the same event scaled up beyond reason, a storm cloud separating charge until the voltage reaches hundreds of millions of volts and the sky finally breaks the air down over a kilometre or more (NSSL, NOAA). A doorknob zap and a lightning bolt are the same physics, one of them just much louder. Current electricity, the kind that runs your building, is the tamed version: charge kept flowing steadily around a closed loop instead of piling up and jumping.

Why copper, when silver conducts better?

Silver is the best metallic conductor there is, and we still wire buildings in copper. That is an economics decision, not a physics one.

On the standard conductivity scale copper is the 100% reference, and silver comes in at about 106% (IACS conductivity). Silver is genuinely better, by roughly six percent. It is also many times the price, softer, and prone to tarnish. Nobody is going to run six percent better conductivity through the walls of a factory at that cost. Copper gives you almost the best conductivity in existence, cheaply, in a metal you can draw into kilometres of flexible wire. It is the rational choice per ringgit, and that is why more than nine wires in ten around you are copper.

What makes the electrons drift at all?

What makes the electrons drift is a push, applied and kept up. We have quietly leaned on that one word this whole time. Something has to lean on that free electron sea to make it drift in one direction rather than jiggle randomly, and something has to keep leaning to keep the current flowing. That push has a name, and so does the flow it produces.

The push is voltage. The flow is current, measured in amperes. Get those two ideas straight and the rest of electrical engineering starts to open up, because almost everything after this is a story about pressure and flow. That is exactly where Volts and Amps picks up.

This is Part 1 of 23 in Cobler's Electricity Fundamentals series. Next: Volts and Amps: Electrical Pressure and Flow, Explained.

Cobler builds CobiNeural, the platform that turns all this invisible electron drift into numbers a facility team can actually act on: real-time energy, demand and power quality across a whole site. If you would rather see your building's electricity than take it on faith, talk to us.