How does a thermostat know the temperature?
The Dancing Metal Strip
How does a thermostat know the temperature?
You walk past the little white box on the wall twenty times a day and never think about it. But right now, at this very second, it's taking your temperature — well, the room's temperature — and deciding whether you need rescuing from the heat or the cold.
Inside that box sits a tiny strip of metal. Actually, it's two different metals — say, brass and steel — pressed together into one ribbon, like a two-layer sandwich. Here's the weird part: when metal gets hot, it expands. When it cools down, it shrinks. You've seen this — a jar lid loosens under hot water, tightens in the cold.
