The burning glass
The experiment shows how people once used to make fire. But how can a magnifying glass and the sun cause the wood to burn?
The burning glass consists of a focussing lens that collects the sun’s rays at a point, the focus. By setting the lens at the correct distance from the piece of wood, you can get the focus to hit the surface of the wood. After a while, the temperature here can then become so high that the wood starts to burn. Burning glasses have been used for thousands of years to start fires.