What is electricity?

Electrons: the charged bits inside every atom

Every atom has a positively charged center (the nucleus) and tiny negatively charged particles around it called electrons. Most electrons are held tightly by their own atom.

In a metal such as copper, things are different. Some of the outer electrons aren't tied to any one atom. These free electrons wander between the atoms all the time. That's what makes metals good conductors: there's already a sea of movable charge inside the wire.

A tube full of marbles

Picture a tube already packed end to end with marbles. Push one marble in at one end, and one pops out the other end almost instantly. The marble you pushed didn't race through the tube; the push passed along the whole row.

A wire works the same way. A battery doesn't send new electrons into an empty wire. It pushes on the electrons that are already there, all around the circuit at once.

Electrons creep, the push races

Here's the surprising part. Each electron only drifts along very slowly. In ordinary household wire carrying about 1 amp, the drift speed is a few hundredths of a millimeter per second, much slower than a snail.

But the push, the electrical signal, travels down the wire at a large fraction of the speed of light (roughly 50 to 99% of it, depending on the cable). So when you flip a switch, the lamp lights at once, even though the electrons near the switch won't reach the lamp for hours.

So what is electricity?

Electricity is that flow of charge, and the energy it carries from the battery or the outlet to whatever you've plugged in, like a lamp, a motor or a phone charger.

Try it yourself

Flip a light switch and watch: the light comes on with no delay you can see, even across a big room. Then remember that the electrons in that wire are moving slower than a snail. What crossed the room in an instant was the push, not the electrons.

Good to know

• This lesson sticks to metal wires, where free electrons carry the current. In other materials, such as salt water or batteries, ions can carry the charge.
• Drift speed in household wiring is tiny: about 23 micrometers per second for 1 A in a 2 mm thick copper wire.
• The signal travels as an electromagnetic wave guided by the wire, at roughly 50 to 99% of the speed of light depending on the cable, so "close to the speed of light" is a simplification.
• The energy actually travels in the electric and magnetic fields around the wire, not inside the electrons.
• Wall outlets supply AC, so the electrons there mostly wiggle back and forth instead of traveling along. AC vs DC comes later in the series.
• The marble picture ignores that free electrons are already zipping around randomly at high speed; the drift is a small net motion on top of that.