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Lesson: Chapter 9 — Heat

9.4. Thermal expansion 4 of 5

The bimetallic strip

Electric irons and rice cookers control their temperature with a bimetallic strip: two metals that expand by different amounts for the same temperature change.

The two strips are riveted together, one end fixed and the other free. When it warms, one strip expands more than the other, and the pair bends.

Figure to be added

Figure 9.20 — (a) a straight bimetallic strip; (b) the same strip bent after heating.

As a switch

Wired into a circuit with a heater, the strip touches a contact while cool. When the temperature passes a set limit it bends away, breaking the circuit and switching the heater off.

Figure to be added

Figure 9.21 — a bimetallic strip in a circuit with a battery and a heater: (a) cool, touching the contact; (b) hot, bent away from it.