A technical model to show the practical use of bimetal strip.
Principle: when a 4.5 battery is connected to the model a current flows through the green bulb and Bi-metal strip to complete circuit 1.
When the tea light, under the Bi-metal strip is lit, it heats it up and bends it in the opposite direction, breaking circuit 1 and connecting circuit 2 (parallel switching).
The current then flows through the red light to the fan, causing it to switch it on and cool the Bi-metal strip down again.
This switches it back to circuit 1 again.
See the following video: