Question

Draw a labelled diagram to show a fire alarm that uses the principle of expansion of heat.

Answer 1

A fire alarm that uses the principle of expansion of heat:



This fire alarm uses the fact that different solids expand by different amount of heating. The alarm contains two metal strips, one of the iron and other of brass, firmly bolted together. Brass expands more on heating, therefore the bimetallic strip bend on the side of iron upon heating and the circuit is completed. Hence, the fire alarm bell rings.