• id: JME-10-N04
• title: Bimetallic Strip — Working Principle
• tags: bimetallic, thermostat, differential-expansion

A bimetallic strip consists of two metals with different $\alpha$ values bonded together. On heating, the metal with higher $\alpha$ expands more, causing the strip to bend toward the metal with lower $\alpha$. On cooling, it bends the other way. Used in thermostats — the strip makes/breaks an electrical contact at a set temperature. Also used in thermal compensation in clocks and as temperature indicators. The radius of curvature of the bent strip: $R \approx t / [(\alpha_2 - \alpha_1)\Delta T]$, where $t$ is the total thickness.