How does a telephone work?

Your voice squeezes a pinch of carbon, a current copies the sound, and a switch that steps once per pulse finds the other phone. A classic phone hangs on a pair of copper wires that run to the exchange. The exchange puts about 48 volts on them.

Read how it works: How does a telephone work? · The history of the telephone · More boxes on Glassbox

Chapters in this interactive model

1. Inside a rotary desk phone: A handset, a hook switch, a dial, two bells and a pair of copper wires.
2. Turning a voice into a current: Carbon granules squeezed by sound, and an electromagnet that pulls it back into sound.
3. Sending a number down two wires: A rotary dial breaks the current in pulses. A keypad sings two notes at once.
4. The exchange connects the call: Operators with plugs, then switches that step with every pulse, then chips.
5. Many calls, one line, across the world: Voices chopped into numbers, taking turns on trunks, cables and satellites.
6. The landline today: Your voice in packets over fibre, why calls sound "telephone-y", and 112.