How does electricity flow?
The short answer
Electricity is the flow of electrons through a conductor. In a metal, free electrons normally jitter at random; a voltage, such as a battery’s, pushes them into a slow drift from − to +. Around a closed loop that drift is an electric current, and where the path is narrow and resistant, the electrons’ collisions turn electrical energy into heat and light.
Chapters and transcript
- 0:00
Metal is full of free electrons
A metal is a lattice of positive ions with loosely held outer electrons wandering between them. With no push, each one jitters at random, so on average nothing flows.
- 0:08
A voltage gives them a push
Connect a battery and the random motion tilts into a slow drift from − towards +. The push is the voltage; how many electrons pass a point each second is the current, measured in amps.
- 0:17
Current flows round a closed loop
Electrons leave the battery’s − terminal, run round the wire and through the bulb, and return to +. The battery keeps the push going, and the current is the same at every point in the loop.
- 0:25
Resistance turns flow into heat
In a thin filament the same number of electrons must squeeze through a narrower path, so they move faster and keep hitting the metal’s ions. That energy comes out as heat and light; the power released is current squared times resistance (I² × R).
- 0:33
Open the loop and it stops at once
A switch opens a gap, and with no closed loop the current stops everywhere. Each electron drifts less than a millimetre a second, but the push travels round the wire at a large fraction of light speed.