What mechanism does a bimetallic strip use to activate an alarm?

The correct answer is based on the fundamental principles of how a bimetallic strip operates. A bimetallic strip is made from two different types of metals that have distinct thermal expansion coefficients. When the strip is subjected to heat, each metal expands at a different rate. This disparity causes the strip to bend, as one metal expands more than the other.

As the temperature increases, the bending action can be harnessed to activate mechanical switches or alarms. This heat-induced bending is a reliable mechanism for temperature sensing, commonly used in devices such as thermostats and fire alarms. Thus, when the bimetallic strip reaches a certain temperature threshold, it bends sufficiently to trigger an alarm, signaling the presence of heat or potential fire conditions. This application leverages the physical properties of metals, making it an effective way to monitor temperature changes in fire detection systems.